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Terminal Step (terminal + step)
Selected AbstractsStructure of Escherichia coli pyridoxine 5,-phosphate oxidase in a tetragonal crystal form: insights into the mechanistic pathway of the enzymeACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2005Faik N. Musayev Escherichia coli pyridoxine 5,-phosphate oxidase (ePNPOx) catalyzes the terminal step in the biosynthesis of pyridoxal 5,-phosphate (PLP) by the FMN oxidation of pyridoxine 5,-phosphate (PNP) or pyridoxamine 5,-phosphate (PMP), forming FMNH2 and H2O2. The crystal structure of ePNPOx is reported in a tetragonal unit cell at 2.6,Å resolution. The three-dimensional fold of this structure is very similar to those of the E. coli and human enzymes that crystallized in trigonal and monoclinic unit cells. However, unlike the previous structures, the tetragonal structure shows major disorder in one of the two subunit domains that has opened up both the active site and a putative tunnel. Comparison of these structures gives an insight into the mechanistic pathway of PNPOx: from the resting enzyme with no substrate bound, to the initial binding of the substrate at the active site, to the catalytic stage and to the release of the catalytic product from the active site. [source] Developmental disorders of glucose metabolism in infantsCHILD: CARE, HEALTH AND DEVELOPMENT, Issue 2002R. Hume Abstract Background Developmental failures to adequately control postnatal blood glucose levels are common in the transition from fetal to infant life and can persist for many months. The standard method of functionally measuring hepatic glucose production and/or disordered glucose production is the response to a glucagon tolerance test. Method We adapted the standard glucagon tolerance test used for children and adults for use in preterm infants. 79 consecutive preterm infants gestational age range 25,36 weeks (mean 32.2 weeks), mean birth weight 1.66 kg admitted to the Neonatal Intensive Care Unit, Ninewells Hospital, Dundee and who survived to discharge home were recruited into the study. At the time of discharge home the characteristics of the group were as follows: adjusted mean gestational age 36.7 weeks, mean discharge weight 2.23 kg. Results In this study of preterm infants the maximal increase in plasma glucose following administration of a glucagon tolerance test is 1.39 ± 07 mmol/L, n = 78 (range 0,3.98 mmol/L). Conclusions An increase in plasma glucose of less than 4 mmol/L is considered abnormal in adults following administration of a fasting glucagon tolerance test. The responses of preterm infants and adults to glucagon are clearly different. The attenuated response to glucagon in the preterm infants is consistent with the low levels of hepatic glucose-6-phosphatase activity in premature infants as glucose-6-phosphatase is the terminal step of the two main pathways of liver glucose production. [source] Mutation spectrum of the glucose-6-phosphatase gene and its implication in molecular diagnosis of Korean patients with glycogen storage disease type IaCLINICAL GENETICS, Issue 6 2004C-S Ki Glycogen storage disease type Ia (GSD Ia; MIM 232200) is an autosomal recessive inherited metabolic disorder resulting from a deficiency of the microsomal glucose-6-phosphatase (G6Pase), the enzyme that catalyzes the terminal step in gluconeogenesis and glycogenolysis. Various mutations in the G6Pase gene (G6PC) have been found in patients with GSD Ia. To elucidate the spectrum of the G6PC gene mutations, 13 unrelated Korean patients with GSD Ia were analyzed. We were able to identify mutant alleles in all patients, including three known mutations (727G > T, G122D, and T255I) and two novel mutations (P178A and Y128X). The frequency of the 727G > T mutation in Korean patients with GSD Ia was 81% (21/26), which was slightly lower than that (86,92%) in Japanese but much higher than that (44.4%) in Taiwan Chinese. Except one, all patients were either homozygous (9/13) or compound heterozygous (3/13) for the 727G > T mutation; the only patient without the 727G > T mutation was a compound heterozygote for the G122D and Y128X mutations. Our findings suggest that a DNA-based test can be used as the initial diagnostic approach in Korean patients clinically suspected to have GSD Ia, thereby avoiding invasive liver biopsy. [source] A Caenorhabditis elegans model of orotic aciduria reveals enlarged lysosome-related organelles in embryos lacking umps-1 functionFEBS JOURNAL, Issue 6 2010Steven Levitte Gut granules are cell type-specific lysosome-related organelles found within the intestinal cells of Caenorhabditis elegans. To investigate the regulation of lysosome-related organelle size, we screened for C. elegans mutants with substantially enlarged gut granules, identifying alleles of the vacuolar-type H+ -ATPase and uridine-5,-monophosphate synthase (UMPS)-1. UMPS-1 catalyzes the conversion of orotic acid to UMP; this comprises the two terminal steps in de novo pyrimidine biosynthesis. Mutations in the orthologous human gene UMPS result in the rare genetic disease orotic aciduria. The umps-1(,) mutation promoted the enlargement of gut granules to 250 times their normal size, whereas other endolysosomal organelles were not similarly affected. UMPS-1::green fluorescent protein was expressed in embryonic and adult intestinal cells, where it was cytoplasmically localized and not obviously associated with gut granules. Whereas the umps-1(,) mutant is viable, combination of umps-1(,) with mutations disrupting gut granule biogenesis resulted in synthetic lethality. The effects of mutations in pyr-1, which encodes the enzyme catalyzing the first three steps of de novo pyrimidine biosynthesis, did not phenotypically resemble those of umps-1(,); instead, the synthetic lethality and enlargement of gut granules exhibited by the umps-1(,) mutant was suppressed by pyr-1(,). In a search for factors that mediate the enlargement of gut granules in the umps-1(,) mutant, we identified WHT-2, an ABCG transporter previously implicated in gut granule function. Our data suggest that umps-1(,) leads to enlargement of gut granules through a build-up of orotic acid. WHT-2 possibly facilitates the increase in gut granule size of the umps-1(,) mutant by transporting orotic acid into the gut granule and promoting osmotically induced swelling of the compartment. [source] The purification, crystallization and preliminary structural characterization of PhzM, a phenazine-modifying methyltransferase from Pseudomonas aeruginosaACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 9 2006Neelakshi Gohain Pyocyanin, phenazine-1-carboxylic acid and more than 70 related compounds collectively known as phenazines are produced by various species of Pseudomonas, including the fluorescent pseudomonad P. aeruginosa, a Gram-negative opportunistic pathogen in humans and animals. P. aeruginosa synthesizes a characteristic blue water-soluble compound called pyocyanin (1-hydroxy-5-methyl-phenazine). Two enzymes designated PhzM and PhzS are involved in the terminal steps of its synthesis and very little is known about these enzymes. In this study, PhzM, a dimeric S -adenosylmethionine-dependent methyltransferase, was purified and crystallized from PEG 3350/sodium cacodylate/sodium citrate pH 6.5. The crystals belong to space group P1, with unit-cell parameters a = 46.1, b = 61.8, c = 69.6,Å, , = 96.3, , = 106.6, , = 106.9°. They contain one dimer in the asymmetric unit and diffract to a resolution of 1.8,Å. Anomalous data to 2.3,Å resolution have been collected from seleno- l -methionine-labelled PhzM. [source] Aldosterone synthase gene variation and adrenocortical response to sodium status, angiotensin II and ACTH in normal male subjectsCLINICAL ENDOCRINOLOGY, Issue 2 2004Brian Kennon Summary objective, Aldosterone synthase, a key enzyme in the terminal steps of aldosterone synthesis, is encoded by the CYP11B2 gene. A polymorphism in the 5, coding region of this gene (,344 C/T) is associated with hypertension, particularly with elevation of the aldosterone to renin ratio. A second polymorphism (a conversion in intron 2 to resemble that of the neighbouring 11,-hydroxylase (CYP11B1) gene) is found in close linkage dysequilibrium with the variant at ,344 C/T. The mechanism by which these variants predispose to cardiovascular disease and the precise intermediate phenotype associated with them remains speculative. design, We performed a focused physiological study in normal volunteers stratified by CYP11B2 genotype. patients, Twenty-three subjects homozygous for the T allele and 21 homozygous for the C allele of the ,344 C/T polymorphism of CYP11B2 were studied. measurements, Basal and angiotensin II stimulated plasma and 24-h urinary steroid excretion during low (60 mmol/day) and high (160 mmol/day) sodium intake and plasma steroids after ACTH stimulation were measured. results, No influence of polymorphic variation on basal or stimulated plasma cortisol or aldosterone or other plasma steroid concentrations during either dietary phase was seen. However, excretion of tetrahydro-11-deoxycortisol (the urinary metabolite of 11-deoxycortisol), which is the precursor of cortisol) was increased in TT subjects during sodium restriction, consistent with impairment of zona fasciculata 11,-hydroxylation. conclusions, We conclude that this polymorphism has no major influence on normal zona glomerulosa function but is associated with a change in 11,-hydroxylation in the zona fasciculata. The mechanism remains uncertain, but alteration of 11-deoxycortisol levels without change in cortisol suggests altered efficiency of 11,-hydroxylation. In the long term, this may lead to a minor but chronic increase in ACTH drive to the gland, which may have consequences for steroid synthesis and predispose to the risk of cardiovascular disease. [source] | ||||||||||