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Acid Plays (acid + play)
Selected AbstractsThe relationship between changes in the cell wall, lipid peroxidation, proliferation, senescence and cell deathPHYSIOLOGIA PLANTARUM, Issue 1 2003Gerhard Spiteller Plants and mammals contain polyunsaturated fatty acids (PUFAs) in their membranes. PUFAs belong to the most oxygen sensitive molecules encountered in nature. It would seem that nature has selected this property of PUFAs for signalling purposes: PUFAs are stored in the surface of cells and organelles not in free form but conjugated to phospho- and galactolipids. Any change in membrane structure apparently activates membrane-bound phospholipases, which cleave the conjugates. The obtained free PUFAs are substrates for lipoxygenases (LOX). These transform PUFAs to lipidhydroperoxides (LOOHs). LOOHs are converted to a great variety of secondary products. These lipid-peroxidation (LPO) products and the resulting generated products thereof represent biological signals, which do not require a preceding activation of genes. They are produced as a non-specific response to a large variety of external or internal impacts, which therefore do not need interaction with specific receptors. When, due to an external impact, e.g. attack of a microorganism, or to a change in temperature, the amount of liberated free PUFAs exceeds a certain threshold, LOX commit suicide. Thus iron ions, located in the active centre of LOX, are liberated. Iron ions react with LOOHs in the close surroundings by generating alkoxy radicals (LO.). These induce a non-enzymatic LPO. A fraction of the LO. radicals generated from linoleic acid (LPO products derived from linoleic acid play a dominant role in signalling which was previously overlooked) is converted to 2,4-dienals which induce the programmed cell death (PCD) and the hypersensitive reaction (HR). While peroxyl radicals (LOO.) generated as intermediates in the course of an enzymatic LPO are transformed within the enzyme complex to corresponding anions (LOO,), and thus lose their reactivity, peroxyl radicals generated in non-enzymatic reactions are not deactivated. They not only react by abstraction of hydrogen atoms from activated X-H bonds of molecules in their close vicinity, but also by epoxidation of double bonds and oxidation of a variety of biological molecules, causing a dramatic change in molecular structure which finally leads to cell death. As long as reducing agents, like glutathione, or compounds with free phenolic groups are available, the amount of LOOHs is kept low. Cell death is induced in a defined way by apoptosis. But when the reducing agents have been consumed, PCD seems to switch to necrotic processes. Thus proliferation is induced by minor changes at the cell membrane, while slow changes at cell membranes are linked with apoptosis (e.g. response to attack of microorganisms or drought) and necrosis (severe wounding), depending only on the amount, but not on the type, of applied stimulus. [source] Expression and regulation of alkaline phosphatases in human breast cancer MCF-7 cellsFEBS JOURNAL, Issue 5 2000Lai-Chen Tsai The effect of retinoic acid and dexamethasone on alkaline phosphatase (AP) expression was investigated in human breast cancer MCF-7 cells. Cellular AP activity was induced significantly by retinoic acid or dexamethasone in a time-dependent and dose-dependent fashion. A marked synergistic induction of AP activity was observed when the cells were incubated with both agents simultaneously. Two AP isozymes, tissue-nonspecific (TNAP) and intestinal (IAP), were shown to be expressed in MCF-7 cells as confirmed by the differential rate of thermal inactivation of these isozymes and RT-PCR. Based on the two-isozyme thermal-inactivation model, the specific activities for TNAP and IAP in each sample were analyzed. TNAP activity was induced only by retinoic acid and IAP activity was induced only by dexamethasone. Whereas dexamethasone conferred no significant effect on TNAP activity, retinoic acid was shown to inhibit IAP activity by , 50%. Interestingly, TNAP was found to be the only isozyme activity superinduced when the cells were costimulated with retinoic acid and dexamethasone. Northern blot and RT-PCR analysis were then used to demonstrate that the steady-state TNAP mRNA level was also superinduced, which indicates that the superinduction is regulated at the transcriptional or post-transcriptional levels. In the presence of the glucocorticoid receptor antagonist RU486, the dexamethasone-mediated induction of IAP activity was blocked completely as expected. However, the ability of RU486 to antagonize the action of glucocorticoid was greatly compromised in dexamethasone-mediated superinduction of TNAP activity. Furthermore, in the presence of retinoic acid, RU486 behaved as an agonist, and conferred superinduction of TNAP gene expression in the same way as dexamethasone. Taken together, these observations suggest that the induction of IAP activity by dexamethasone and the superinduction of TNAP by dexamethasone were mediated through distinct regulatory pathways. In addition, retinoic acid plays an essential role in the superinduction of TNAP gene expression by enabling dexamethasone to exert its agonist activity, which otherwise has no effect. [source] Redox and antioxidant systems of the malaria parasite Plasmodium falciparumMOLECULAR MICROBIOLOGY, Issue 5 2004Sylke Müller Summary The malaria parasite Plasmodium falciparum is highly adapted to cope with the oxidative stress to which it is exposed during the erythrocytic stages of its life cycle. This includes the defence against oxidative insults arising from the parasite's metabolism of haemoglobin which results in the formation of reactive oxygen species and the release of toxic ferriprotoporphyrin IX. Central to the parasite's defences are superoxide dismutases and thioredoxin-dependent peroxidases; however, they lack catalase and glutathione peroxidases. The vital importance of the thioredoxin redox cycle (comprising NADPH, thioredoxin reductase and thioredoxin) is emphasized by the confirmation that thioredoxin reductase is essential for the survival of intraerythrocytic P. falciparum. The parasites also contain a fully functional glutathione redox system and the low-molecular-weight thiol glutathione is not only an important intracellular thiol redox buffer but also a cofactor for several redox active enzymes such as glutathione S-transferase and glutaredoxin. Recent findings have shown that in addition to these cytosolic redox systems the parasite also has an important mitochondrial antioxidant defence system and it is suggested that lipoic acid plays a pivotal part in defending the organelle from oxidative damage. [source] Binding of the periodontitis associated bacterium Porphyromonas gingivalis to glycoproteins from human epithelial cellsMOLECULAR ORAL MICROBIOLOGY, Issue 5 2008U. Hallén Introduction:, In the present study we examined the ability of the periodontal pathogen Porphyromonas gingivalis to adhere to glycoconjugates on intact cells and to protein preparations of epithelial cells (KB cells). Methods:, The KB cell protein preparation was separated by sodium dodecyl sulfate,polyacrylamide gel electrophoresis and transferred to nitrocellulose membranes by Western blotting. The membranes were used in overlay assays with labeled P. gingivalis. Flow cytometry was used to analyze attachment of bacteria to intact KB cells. Results:, Glycoconjugate expression on the KB cells and in the protein preparation was confirmed. Binding was detected to several bands on the Western blots. Flow cytometry showed a distinct increase in fluorescence for strain FDC 381. Preincubation of the bacteria with mannose, fucose, N -acetylglucosamine and N -acetylgalactosamine inhibited the binding to KB cells by approximately 30% whereas preincubation with N -acetylneuraminic acid reduced the binding by 60%. Conclusion:, These results indicate that carbohydrate structures are involved in the binding process of P. gingivalis to oral epithelial cells and that neuraminic acid plays a significant role in the adhesion process. [source] | ||||||||||