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Aminolevulinic Acid (aminolevulinic + acid)
Selected AbstractsIn Vivo Pharmacokinetics of ,-Aminolevulinic Acid,Induced Protoporphyrin IX During Pre- and Post-Photodynamic Therapy in 7,12-Dimethylbenz(a)nthracene-Treated Skin Carcinogenesis in Swiss Mice: A Comparison by Three-Compartment Model,,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2002Parmeswaran Diagaradjane ABSTRACT ,-Aminolevulinic acid,photodynamic therapy (ALA-PDT) has emerged as a useful technique in the treatment of superficial basal cell carcinoma, actinic keratosis, squamous cell carcinoma and tumors of other organs. Earlier reports mention that there is reappearance of protoporphyrin IX (PpIX) after photoirradiation of tumors. This property of reappearance of PpIX is being utilized to treat nodular tumors by fractionated light dose delivery. However, there is still no unanimously accepted reason for this reappearance phenomenon and the rate of resynthesis after PDT. On account of this, studies are carried out on the estimation of the pharmacokinetics of the ALA-induced PpIX in mice tumor models and the surrounding normal tissues before and after PDT. Further, a mathematical model based on a multiple compartment system is proposed to estimate the rate parameter for the diffusion of PpIX from the surrounding normal tissues into the tumor tissue (km) caused by photobleaching during PDT with irradiating fluences of 36.0 and 57.6 J/cm2. The km value at two different fluences, 36.0 and 57.6 J/cm2, are estimated as 3.0636 ± 0.7083 h,1 and 6.9231 ± 2.17651 h,1, respectively. Further, the rate parameter for the cleavage and efflux of ALA (k1) and the rate parameter for the evasion of PpIX from the tumor tissues after PDT (kt) were also estimated by fitting the experimental data to the developed mathematical model. The statistical significance of the estimated parameters was determined using Student's t -test. The experimental results and the rate parameters obtained using the proposed compartment model suggest that in addition to the earlier reported reasons, the invasion or diffusion of PpIX from the surrounding tissues to the tumor tissues after photoirradiation might also contribute to the reappearance of PpIX after PDT. [source] Stability of 5-aminolevulinic acid in novel non-aqueous gel and patch-type systems intended for topical applicationJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2005Paul A. McCarron Abstract Aminolevulinic acid (ALA) stability within topical formulations intended for photodynamic therapy (PDT) is poor due to dimerisation to pyrazine-2,5-dipropionic acid (PY). Most strategies to improve stability use low pH vehicles, which can cause cutaneous irritancy. To overcome this problem, a novel approach is investigated that uses a non-aqueous vehicle to retard proton-induced charge separation across the 4-carbonyl group on ALA and lessen nucleophilic attack that leads to condensation dimerisation. Bioadhesive anhydrous vehicles based on methylvinylether-maleic anhydride copolymer patches and poly(ethyleneglycol) or glycerol thickened poly(acrylic acid) gels were formulated. ALA stability fell below pharmaceutically acceptable levels after 6 months, with bioadhesive patches stored at 5°C demonstrating the best stability by maintaining 86.2% of their original loading. Glycerol-based gels maintained 40.2% in similar conditions. However, ALA loss did not correspond to expected increases in PY, indicating the presence of another degradative process that prevented dimerisation. Nuclear magnetic resonance (NMR) analysis was inconclusive in respect of the mechanism observed in the patch system, but showed clearly that an esterification reaction involving ALA and both glycerol and poly(ethyleneglycol) was occurring. This was especially marked in the glycerol gels, where only 2.21% of the total expected PY was detected after 204 days at 5°C. Non-specific esterase hydrolysis demonstrated that ALA was recoverable from the gel systems, further supporting esterified binding within the gel matrices. It is conceivable that skin esterases could duplicate this finding upon topical application of the gel and convert these derivatives back to ALA in situ, provided skin penetration is not affected adversely. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1756,1771, 2005 [source] In Vivo Pharmacokinetics of ,-Aminolevulinic Acid,Induced Protoporphyrin IX During Pre- and Post-Photodynamic Therapy in 7,12-Dimethylbenz(a)nthracene-Treated Skin Carcinogenesis in Swiss Mice: A Comparison by Three-Compartment Model,,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2002Parmeswaran Diagaradjane ABSTRACT ,-Aminolevulinic acid,photodynamic therapy (ALA-PDT) has emerged as a useful technique in the treatment of superficial basal cell carcinoma, actinic keratosis, squamous cell carcinoma and tumors of other organs. Earlier reports mention that there is reappearance of protoporphyrin IX (PpIX) after photoirradiation of tumors. This property of reappearance of PpIX is being utilized to treat nodular tumors by fractionated light dose delivery. However, there is still no unanimously accepted reason for this reappearance phenomenon and the rate of resynthesis after PDT. On account of this, studies are carried out on the estimation of the pharmacokinetics of the ALA-induced PpIX in mice tumor models and the surrounding normal tissues before and after PDT. Further, a mathematical model based on a multiple compartment system is proposed to estimate the rate parameter for the diffusion of PpIX from the surrounding normal tissues into the tumor tissue (km) caused by photobleaching during PDT with irradiating fluences of 36.0 and 57.6 J/cm2. The km value at two different fluences, 36.0 and 57.6 J/cm2, are estimated as 3.0636 ± 0.7083 h,1 and 6.9231 ± 2.17651 h,1, respectively. Further, the rate parameter for the cleavage and efflux of ALA (k1) and the rate parameter for the evasion of PpIX from the tumor tissues after PDT (kt) were also estimated by fitting the experimental data to the developed mathematical model. The statistical significance of the estimated parameters was determined using Student's t -test. The experimental results and the rate parameters obtained using the proposed compartment model suggest that in addition to the earlier reported reasons, the invasion or diffusion of PpIX from the surrounding tissues to the tumor tissues after photoirradiation might also contribute to the reappearance of PpIX after PDT. [source] Photodynamic Therapy for the Treatment of Cutaneous Neoplasia, Inflammatory Disorders, and PhotoagingDERMATOLOGIC SURGERY, Issue 5 2009EMILY TIERNEY MD BACKGROUND Photodynamic therapy (PDT) has demonstrated high efficacy, minimal side effects, and improved cosmetic outcome when used for the treatment of actinic keratoses (AK), basal cell carcinoma (BCC), squamous cell carcinoma, and photoaging. METHODS To review the literature on the use of PDT in dermatologic surgery using MEDLINE. RESULTS Published clinical studies using PDT in the treatment of AKs yield overall efficacy rates ranging from 50% to 71% with one treatment to as high as 88% to 90% with two or more treatments. For superficial BCC, initial clearance rates were 76% to 97%, and for Bowen's disease, initial clearance rates ranged from 72% to 94% overall. The use of PDT for photorejuvenation is a relatively new application of this technology, which has shown promise in improving the appearance of fine lines, pigmentary variation, and telangiectasias. CONCLUSIONS The advantages of photodynamic therapy include the capacity for noninvasive targeted therapy through topical application of aminolevulinic acid and methyl aminolevulinic acid, with outstanding cosmetic results. Although the theory behind the use of chemical photosensitizers and ultraviolet light to treat a wide variety of skin disorders is straightforward, the practical application of this technology is evolving. Additional research into the precise mechanisms of action for specific photosensitizers and optimal light sources will be highly beneficial to the advancement of this technology. [source] Aminolevulinic acid-loaded Witepsol microparticles manufactured using a spray congealing procedure: implications for topical photodynamic therapyJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 9 2009Rasil Al-Kassas Abstract Objectives The aim was to enhance aminolevulinic acid (ALA) stability by incorporation into low-melting microparticles prepared using a spray congealing procedure and to evaluate temperature-triggered release, allowing topical bioavailability following melting at skin temperature. Methods ALA-loaded Witepsol microparticles were prepared using a novel spray congealing technique. Entrapment efficiency was compared with conventional emulsion-based methods and modelled drug release profiles determined using a membrane separation technique. Raised receiver medium temperature was used to determine triggered release. Bioavailability and lipid-mediated enhancement of ALA penetration were determined in excised murine skin. Key findings ALA-loaded Witepsol microparticles were spherical, with a mean diameter of 20 ,m. Loading and stability studies demonstrated effective encapsulation, ranging from 91% to 100%, with no evidence of degradation to pyrazine derivatives. ALA release correlated with dissolution medium temperature, triggered at temperatures close to that of skin. Results suggested that molten Witepsol enhanced cutaneous permeation, whereas incorporation of microparticles in a semi-solid vehicle attenuated ALA penetration. Optimal use was direct application under occlusion. Conclusions Spray congealing is superior to the emulsion-based procedures with respect to encapsulation efficiency of ALA in Witepsol matrices, providing temperature-triggered release, enhanced stability and improved penetration of ALA through keratinised skin. These features could improve ALA delivery to superficial lesions as part of photodynamic therapy. [source] A review of photodynamic therapy in cutaneous leishmaniasisJOURNAL OF THE EUROPEAN ACADEMY OF DERMATOLOGY & VENEREOLOGY, Issue 8 2008EM Van Der Snoek Summary We present a review of six clinical studies investigating the use of photodynamic therapy (PDT) using porphyrin precursors for the treatment of Old World cutaneous leishmaniasis (CL). Thirty-nine patients with a total of 77 lesions received PDT using a range of treatment schedules following topical application of aminolevulinic acid (ALA) or methyl-aminolevulinate (MAL). The tissue response to PDT is accompanied by a mild burning sensation, erythema and reversible hypo- and hyperpigmentation. Few mechanistic studies have addressed the principles underlying the use of PDT for CL. All six reviewed papers suggest that PDT with porphyrin precursors is relatively effective in treating CL. Data are still limited, and PDT cannot at this point be recommended in routine clinical practice. The mechanism of action of this promising therapeutic modality needs to investigated further and additional controlled trials need to be performed. [source] Evidence-based review of lasers, light sources and photodynamic therapy in the treatment of acne vulgarisJOURNAL OF THE EUROPEAN ACADEMY OF DERMATOLOGY & VENEREOLOGY, Issue 3 2008M Hædersdal Abstract Background, There is a considerable need for effective and safe treatment for acne vulgaris. Objective, In a systematic review with an evidence-based approach to assess the effects of optical treatments for acne vulgaris. Methods, Original publications of controlled clinical trials were identified through searches in PubMed and the Cochrane Library. Results, A total of 16 randomized controlled trials (RCT) and 3 controlled trials (CT) were identified, involving a total of 587 patients. Interventions included photodynamic therapy (PDT; 5 RCTs), infrared lasers (4 RCTs), broad-spectrum light sources (3 RCTs, 1 CT), pulsed dye lasers (PDL; 2 RCTs, 1 CT), intense pulsed light (IPL; 1 RCTs, 2 CTs), and potassium titanyl phosphate laser (1 RCT). The randomization method was mentioned in 6 of 16 RCTs, and one trial described adequate allocation concealment. Most trials were intraindividual trials (12 of 19), which applied blinded response evaluations (12 of 19) and assessed a short-term efficacy up to 12 weeks after treatment (17 of 19). Based on the present best available evidence, we conclude that optical treatments possess the potential to improve inflammatory acne on a short-term basis with the most consistent outcomes for PDT [up to 68% improvement, aminolevulinic acid (ALA), methyl-aminolevulinic acid (MAL) and red light]. IPL-assisted PDT seems to be superior to IPL alone. Only two trials compare optical vs. conventional treatments, and further studies are needed. Side-effects from optical treatments included pain, erythema, oedema, crusting, hyperpigmentation, pustular eruptions and were more intense for treatments combined with ALA or MAL. Conclusion, Evidence from controlled clinical trials indicates a short-term efficacy from optical treatments for acne vulgaris with the most consistent outcomes for PDT. We recommend that patients are preoperatively informed of the existing evidence, which indicates that optical treatments today are not included among first line treatments. [source] Photodynamic therapy: update 2006 Part 2: Clinical resultsJOURNAL OF THE EUROPEAN ACADEMY OF DERMATOLOGY & VENEREOLOGY, Issue 4 2007PG Calzavara-Pinton Abstract In several randomized, controlled studies, the application of a standard preparation containing methyl-aminolevulinate (MAL; Metvix®, Galderma, F), followed by red light irradiation proved effective and well tolerated in the treatment of actinic keratosis and basal cell carcinoma, and has now been approved for clinical use in European countries. A brand name aminolevulinic acid (ALA) solution (Levulan Kerastick®, Dusa Pharmaceuticals Inc., Wilmington, MA) plus blue light exposure has been approved for the treatment of actinic keratosis in the USA. Randomized and controlled studies have shown that MAL as well as ALA are also effective in the treatment of Bowen's disease. In addition, a large and growing number of open studies or case reports have evaluated its use in the treatment of a broad range of other neoplastic, inflammatory and infectious skin diseases. However, efficacy and definite advantages over standard therapies remain to be clarified because the experimental design of these studies was often poor, the number of enrolled patients was generally low, and the follow-up was shorter than 12 months. However, these studies have suggested a few possible clinical applications worthy of further investigation. A growing number of laboratory and clinical findings suggest that several new synthetic sensitizers, besides ALA and MAL, may be helpful in the treatment of non-melanoma skin cancers, melanoma metastasis, and selected inflammatory and infective skin diseases. These compounds are deliverable intravenously, have short half-lives both in the blood and skin, and are highly efficient. However, they are as of yet not approved for clinical use. [source] Porphyrin distribution after topical aminolevulinic acid in a novel porcine model of sebaceous skin,,LASERS IN SURGERY AND MEDICINE, Issue 2 2009Fernanda H. Sakamoto MD Abstract Background and Objective Aminolevulinic acid photodynamic therapy (ALA-PDT) depends on drug metabolism into porphyrins. Clinically, ALA-PDT has been used with a wide range of protocols for treating both epidermal and dermal targets, despite limited understanding of porphyrin biodistribution over time. We studied porphyrin accumulation after topical application of ALA in vivo, and also describe the porcine ear as a new animal model to study adnexal glands. Study Design/Materials and Methods The microanatomy of anterior ear skin of swine was measured. Topical 20% ALA in water/ethanol was applied under occlusion. Biopsies taken after 5, 10, 15, and then every 15 minutes for a total of 3 hours were examined by fluorescence microscopy of frozen sections to assess accumulation and distribution of porphyrins. Results Porphyrin fluorescence of digital photomicrograph images was not visually apparent until 30,45 minutes after application, although quantitative pixel analysis showed a statistically significant increase in epidermal fluorescence only 15 minutes after ALA application. From 30 to 120 minutes, epidermis, hair follicles (HF), and sebaceous glands (SG) became progressively more fluorescent. Eccrine gland fluorescence began to be detected after 30 minutes; SG showed fluorescence starting at 45,75 minutes. Fluorescence in all sites reached maximum intensity from 75 to 180 minutes of incubation. There was a trend for HF and SG to express stronger fluorescence compared with epidermis and eccrine glands. Conclusion Anterior pig ear skin is microanatomically similar to human sebaceous skin. The time-dependent accumulation of porphyrins in pilosebaceous units and eccrine glands in this model suggests other routes of uptake of topical ALA in addition to the trans-epidermal route. Apparently, time interval between ALA application and light exposure could be optimized for different uses of ALA-PDT. Lasers Surg. Med. 41:154,160, 2009. © 2009 Wiley-Liss, Inc. [source] Combination of Er:YAG laser and photodynamic therapy in the treatment of nodular basal cell carcinomaLASERS IN SURGERY AND MEDICINE, Issue 2 2008Roman, mucler PhD Abstract Backgrounds and Objectives Photodynamic therapy (PDT), via topical aminolevulinic acid (ALA) is an effective treatment for basal cell carcinomas not exceeding a depth of 2 mm. This limits the treatment of basal cell carcinoma (non-melanoma skin cancer) to superficial forms and nodular therapy (only in aesthetically desired locations). This paper addresses the effectiveness of reducing tumor mass via initial Er:YAG laser ablation to depths that are therapeutically responsive to PDT with ALA. Study Design/Materials and Methods This study compared three methods for the treatment of recurring nodular basal cell carcinomas (r nBCC). Method A utilized PDT with topical application of ALA methyl ester, method B with solitary Er:YAG laser ablation, and method C combined Er:YAG laser ablation reducing tumor size below 2 mm (method B) with subsequent ALA methyl ester PDT (method A). All three methods were used to treat to each patient, all subjects presenting with three or more basal cell carcinomas in order to eliminate differences in patient responsiveness to treatment. Patients were monitored and interviewed at 3, 6, and 12 month intervals to examine the progress of tumor elimination, aesthetic results as well as the patient's preference of treatment method. In all, 286 patients were treated, of whom 194 were checked at the prescribed intervals and then evaluated. Results Statistically, the combination therapy demonstrated the most effective treatment at all time intervals, with a final efficacy of 98.97% versus 94.85% (PDT only) and 91.75% (Er:YAG laser only). The combined method also provided the best aesthetic results (scale: 1,best; 4,worst) of 1.23±1.23, compared to 1.67±0.76 (PDT only) and 1.83±0.95 (Er:YAG laser only). Conclusions Although 67% patients preferred solitary Er:YAG laser treatment over the PDT method (20%) and the combined treatment (13%), because of the simplicity of the treatment, the combination therapy has proven to be both clinically and aesthetically superior. Solitary Er:YAG laser ablation will remain however a fast, effective, and economical treatment alternative for simple manifestations of superficial basal cell carcinoma and has replaced PDT for uncomplicated cases at our facility. The combination of Er:YAG laser ablation and ALA,PDT aspires to be therapy of choice for BCC. Lesers Surg. Med. 40:153,158, 2008. © 2008 Wiley-Liss, Inc. [source] Photodynamic therapy of newly implanted glioma cells in the rat brainLASERS IN SURGERY AND MEDICINE, Issue 5 2006Steen J. Madsen PhD Abstract Background and Objective A syngeneic rat brain tumor model is used to investigate the effects of aminolevulinic acid (ALA)-mediated photodynamic therapy (PDT) on small clusters of tumor cells sequestered in normal brain. Study Design/Materials and Methods Biodistribution studies on tumor-bearing animals were undertaken in order to determine the occurrence of photosensitizer in tumor cells invading normal brain. ALA,PDT toxicity in normal brain and gross tumor were evaluated from histopathology. Effects of PDT on isolated glioma cells in normal brain were investigated by treating animals 48 hours after tumor cell implantation. Results Fluorescence microscopy of frozen tissue sections showed that photosensitizer content was limited and variable in tumor tissue invading normal brain. ALA,PDT with high light doses resulted in significant damage to both gross tumor and normal brain, however, the treatment failed to prolong survival of animals with newly implanted glioma cells. In contrast, animals inoculated with tumor cells pre-incubated in vitro with ALA showed a significant survival advantage in response to PDT. Conclusion The results show that ALA,PDT could not prevent tumors from forming if treatment was performed shortly after tumor initiation. This was likely due to inadequate levels of ALA/PpIX in the glioma cells. Lasers Surg. Med. © 2005 Wiley-Liss, Inc. [source] Porphyrin Bleaching and PDT-induced Spectral Changes are Irradiance Dependent in ALA-sensitized Normal Rat Skin In Vivo,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2001Jarod C. Finlay ABSTRACT Photobleaching kinetics of aminolevulinic acid,induced protoporphyrin IX (PpIX) were measured in the normal skin of rats in vivo using a technique in which fluorescence spectra were corrected for the effects of tissue optical properties in the emission spectral window through division by reflectance spectra acquired in the same geometry and wavelength interval and for changes in excitation wavelength optical properties using diffuse reflectance measured at the excitation wavelength. Loss of PpIX fluorescence was monitored during photodynamic therapy (PDT) performed using 514 nm irradiation. Bleaching in response to irradiances of 1, 5 and 100 mW cm,2 was evaluated. The results demonstrate an irradiance dependence to the rate of photobleaching vs irradiation fluence, with the lowest irradiance leading to the most efficient loss of fluorescence. The kinetics for the accumulation of the primary fluorescent photoproduct of PpIX also exhibit an irradiance dependence, with greater peak accumulation at higher irradiance. These findings are consistent with a predominantly oxygen-dependent photobleaching reaction mechanism in vivo, and they provide spectroscopic evidence that PDT delivered at low irradiance deposits greater photodynamic dose for a given irradiation fluence. We also observed an irradiance dependence to the appearance of a fluorescence emission peak near 620 nm, consistent with accumulation of uroporphyrin/coproporphyrin in response to mitochondrial damage. [source] Response of vulval lichen sclerosus and squamous hyperplasia to photodynamic treatment using sustained topical delivery of aminolevulinic acid from a novel bioadhesive patch systemPHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 2 2009Agnieszka A. Zawislak This study evaluated the clinical and histopathological responses of vulval lichen sclerosus (LS) and squamous hyperplasia (SH) to photodynamic therapy (PDT). A novel bioadhesive patch containing aminolevulinic acid (ALA) at a dose of (38 mg/cm2) was used to treat 10 patients before irradiation with light of 630 nm. Clinical, histopathological and pathological responses to treatment were assessed at 6 weeks post-treatment. After 17 cycles of PDT, six patients reported significant symptomatic relief and no cutaneous photosensitivity. Histopathological differences were not demonstrated, but statistically significant induction of apoptosis was seen. It can be concluded that ALA-PDT patch-based formulation is pragmatic and primarily offers symptomatic management of vulval LS and SH. [source] Phototoxicity of exogenous protoporphyrin IX and ,-aminolevulinic acid in the photo hen's egg testPHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 5 2004Norbert J. Neumann Background: Oxygen, appropriate light sources, and special photosensitizers are necessary to induce photochemical damage in tumor cells via photodynamic therapy (PDT) ,-aminolevulinic acid (ALA) is increasingly used in PDT, because topical or systemic administration of ALA induces accumulation of endogenous porphyrins preferentially in neoplastic tissues. Subsequent radiation with light of approximately 630 nm leads to selective damage of tumor cells. PDT should optimally leave peritumoral tissues unaffected, but only few data are reported on the effects and the time course of ALA-induced porphyrins in tumor-free tissues. Methods: Therefore, we studied the phototoxic effects of protoporphyrin IX (PP) and ALA-induced porphyrins in a recently established photototoxic model based on tumor-free tissue, the photo hen's egg test (PHET). Results: Employing this test procedure, PP provoked strong phototoxic reactions when irradiated with Ultraviolet A immediately and up to 30 h after substance application. In contrast, ALA induced a significant phototoxic effect only if irradiated 24 h after application. Conclusion: Thus, we observed a delayed phototoxic effect of ALA in tumor-free tissue of the yolk sac (YS) blood vessel system. This delayed phototoxic response 24 h after ALA application is probably caused by endogenously synthesized porphyrins. In contrast, epithelial tumors show a maximum porphyrin accumulation 4,8 h after ALA application whereas in healthy human skin porphyrin synthesis is less intensive but prolonged with maximum levels 24,48 h after ALA application. Thus, ALA induced virtually the same delayed phototoxic effect in the tumor-free YS blood vessel tissue as in healthy human skin. These results show that the PHET is a useful model for the predictive preclinical risk assessment of exogenous or endogenous photosensitizers. [source] Protochlorophyllide-independent import of two NADPH:Pchlide oxidoreductase proteins (PORA and PORB) from barley into isolated plastidsPHYSIOLOGIA PLANTARUM, Issue 3 2000Clas Dahlin The enzyme catalysing the reduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide), NADPH:Pchlide oxidoreductase (POR; EC 1.6.99.1), is a nuclear-encoded protein that is post-translationally imported to the plastid. In barley and Arabidopsis thaliana, the reduction of Pchlide is controlled by two different PORs, PORA and PORB. To characterise the possible Pchlide dependency for the import reaction, radiolabelled precursor proteins of barley PORA and PORB (pPORA and pPORB, respectively) were used for in vitro assays with isolated plastids of barley and pea with different contents of Pchlide. To obtain plastids with different endogenous levels of Pchlide, several methods were used. Barley plants were grown in darkness or in greenhouse conditions for 6 days. Alternatively, greenhouse-grown pea plants were incubated for 4 days in darkness before plastid isolation, or chloroplasts isolated from greenhouse-grown plants were incubated with , -aminolevulinic acid (ALA), an early precursor in the Chl biosynthesis resulting in elevated Pchlide contents in the plastids. Both barley pPORA and pPORB were effectively imported into barley and pea chloroplasts isolated from the differentially treated plants, including those isolated from greenhouse-grown plants. The absence or presence of Pchlide did not significantly affect the import capacity of barley pPORA or pPORB. Assays performed on stroma-enriched fractions from chloroplasts and etioplasts of barley indicated that no post-import degradation of the proteins occurred in the stroma, irrespective of whether the incubation was performed in darkness or in light. [source] Concurrent interactions of heme and FLU with Glu tRNA reductase (HEMA1), the target of metabolic feedback inhibition of tetrapyrrole biosynthesis, in dark- and light-grown Arabidopsis plantsTHE PLANT JOURNAL, Issue 6 2004David Goslings Summary The regulation of tetrapyrrole biosynthesis in higher plants has been attributed to metabolic feedback inhibition of Glu tRNA reductase by heme. Recently, another negative regulator of tetrapyrrole biosynthesis has been discovered, the FLU protein. During an extensive second site screen of mutagenized flu seedlings a suppressor of flu, ulf3, was identified that is allelic to hy1 and encodes a heme oxygenase. Increased levels of heme in the hy1 mutant have been implicated with inhibiting Glu tRNA reductase and suppressing the synthesis of , -aminolevulinic acid (ALA) and Pchlide accumulation. When combined with hy1 or ulf3 upregulation of ALA synthesis and overaccumulation of protochlorophyllide in the flu mutants were severely suppressed supporting the notion that heme antagonizes the effect of the flu mutation by inhibiting Glu tRNA reductase independently of FLU. The coiled-coil domain at the C-terminal end of Glu tRNA reductase interacts with FLU, whereas the N-terminal site of Glu tRNA reductase that is necessary for the inhibition of the enzyme by heme is not required for this interaction. The interaction with FLU is specific for the Glu tRNA reductase encoded by HEMA1 that is expressed in photosynthetically active tissues. FLU seems to be part of a second regulatory circuit that controls chlorophyll biosynthesis by interacting directly with Glu tRNA reductase not only in etiolated seedlings but also in light-adapted green plants. [source] | |||||||||||||