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At least 163 records · Page 9Linked to original sources
PubMed1977

Formiminotransferase-cyclodeaminase from porcine liver. A sulfhydryl essential for the deaminase activity of the bifunctional enzyme.

Reaction of the bifunctional enzyme formiminoglutamate:tetrahydrofolate formiminotransferase (EC 2.1.2.5) - formiminotetrahydrofolate cyclodeaminase (EC 4.3.1.4) with the sulfhydryl reagent 5,5'-dithiobis (2-nitrobenzoic acid) selectively inactivates the cyclodeaminase. Loss of activity correlates with the modification of two sulfhydryl groups per subunit. The inhibitor folic acid reduces the rates of inactivation and sulfhydryl modification, and protection experiments demonstrate that only one of the two sulfhydryls modified is important for enzyme activity. The results indicate the presence of a cyclodeaminase site on each polypeptide, assuming one sulfhydryl per site, in agreement with a quaternary structure containing identical polypeptides. Modification does not cause dissociation of the enzyme and is reversible with dithiothreitol.

Ammonia-Lyases↗
PubMed1985

Vitamin B12-folate interrelationships.

The studies discussed in this review support the view that biochemical and clinical symptoms common to both folate and vitamin B12 deficiency are due to the induction of a functional folate deficiency, which in turn is induced by cobalamin deprivation. The interrelationship between these two vitamins is best explained by the methyl trap hypothesis stating that vitamin B12 deficiency can lead to lowered levels of methionine synthetase, which results in a functional folate deficiency by trapping an increased proportion of folate as the 5-methyl derivative. In addition, as 5-methyl-H4PteGlu is a poor substrate for folylpolyglutamate synthetase, there is a decreased synthesis of folylpolyglutamates and consequently a decreased retention of folates by tissues. The real folate deficiency that ensues because of decreased tissue folate levels is probably as important physiologically as the functional deficiency caused by the methyl trap. The sparing effect of methionine can be explained by adenosylmethionine inhibition of methylenetetrahydrofolate reductase, which would prevent the buildup of 5-methyl-H4PteGlun. A deficiency in vitamin B12 would not, in itself, be sufficient to cause a disturbance in folate metabolism. The deficiency would have to result in lowered methyltransferase levels before any such disturbance would be manifest.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed2006

A folate-dependent metabolite in amniotic fluid from pregnancies with normal or trisomy 21 chromosomes.

INTRODUCTION: Previous studies have given conflicting results as to whether or not folate metabolism is altered in Down syndrome. Folate is necessary to facilitate metabolism of one-carbon units. Folate accepts one-carbon units from one-carbon unit donors, including formiminoglutamate (FIGLU). Folate deficiency leads to accumulation of FIGLU and impairment of one-carbon unit metabolism. FIGLU is a functional measure of folate deficiency. MATERIALS AND METHODS: Archived anonymized amniotic fluid specimens were obtained from normal pregnancies and those with Down syndrome. Gas liquid chromatography/mass spectrometry was used to quantitate FIGLU, which is elevated in folate deficiency. A tetra-deuterated FIGLU was used as a standard, and single-ion monitoring was performed. Nonparametric statistical analysis was performed with the Mann-Whitney U test. RESULTS: FIGLU was significantly lower in pregnancies with Down syndrome. The median FIGLU level was 0.9 micromol/l in amniotic fluid from fetuses with Down syndrome. The median FIGLU level was 1.3 in amniotic fluid from control fetuses. This difference was statistically significant (p = 0.009). No statistically significant differences were found with histidine or glutamate. DISCUSSION: There was no evidence of folate deficiency. FIGLU was decreased, not increased. Decreased FIGLU might result from accelerated activity of one or more genes on chromosome 21, by a gene dosage effect. Genes which might explain the reduced FIGLU include one which degrades FIGLU (glutamate formiminotransferase-cyclodeaminase), one which participates in purine synthesis, and one which degrades homocysteine (cystathionine-beta-synthase).

Amniocentesis↗
PubMed1980

A liver urocanase deficiency.

Two sisters with a rare inborn error of histidine metabolism resulting from urocanase deficiency are being presented. The more common form of familial histidinemia due to histidase deficiency is excluded. The urocanase deficiency is proven by demonstrating increased excretion of metabolites of the product of the urocanase enzyme action. Further, the strongest evidence for the urocanase defect rests on the demonstration of urocanase deficiency and normal histidase activity in liver.

Adolescent↗
PubMed1976

Formiminotransferase cyclodeaminase from porcine liver. An octomeric enzyme containing bifunctional polypeptides.

The forminiminotransferase-cyclodeaminase complex contains 2.8% carbohydrate and is composed of identical subunits based on molecular weight, isoelectric focusing and the number of CNBr-generated peptides. Electron microscopy demonstrated that the complex is a ring-shaped molecule when negatively stained both in solution and in crystalline structures. Rotational reinforcement of electron micrographs reveals that the molecule is composed of eight subunits arranged in a planar ring. These results indicate that each polypeptide of the complex must contain both enzymic activities.

Amino Acids↗
PubMed1979

Histidine degradation enzymes in rat liver: induction by high protein intake.

High protein dietary content stimulates urea formation in ureotelic animals but does not exert almost any effect on ammonia production from L-amino acids in vitro. L-histidine and L-threonine are the only amino acids which are most actively deaminated by ureotelic animals fed on a high protein diet. All the steps of L-histidine metabolism have been studied: it has been found that both the histidine transaminase pathway and the histidase pathway are stimulated. Glutamic acid is also a product of histidine catabolism through the histidase pathway, but its catabolism is unaffected by the dietary protein content. These data suggest the existence of independent mechanism controlling the catabolism of the two amino acids.

Aminohydrolases↗
PubMed1982

Histidine dissimilation in Streptomyces coelicolor.

A growth technique that allows strains of Streptomyces coelicolor to grow dispersed in defined liquid medium has been devised and used to determine the pathway of histidine degradation by S. coelicolor. Enzymic, chromatographic and stoichiometric analyses indicated that histidine is dissimilated via N-formyl-L-glutamic acid. The enzymes for histidine utilization (hut) are induced when histidine or urocanate is included in the culture medium. Biochemical evidence suggested that urocanate, or a further metabolite, is the physiological inducer. Three hut mutants were isolated and characterized. Two of the mutants exhibit an uninducible phenotype, whereas the third mutant appears to be defective in the structural gene for formiminoglutamate iminohydrolase. Haploid recombinant analysis was employed to locate all three mutations in the left empty region of the chromosomal map.

Amidohydrolases↗
PubMed1985

Disturbances in histidine metabolism in children with speech abnormalities.

Catabolism of histidine was investigated in 24 patients with different speech and language disorders and with significantly low histidase activity in stratum corneum. No classical histidinemia was found. Biochemical investigation of these patients after loading with L-histidine led to the conclusions that low histidase activity in stratum corneum was connected with: disturbances in folic acid metabolism (2 cases); "atypical histidinemia" (1 case); heterozygotes of histidinemia (2 cases); normal liver histidine metabolism but abnormal in other tissues (18 cases); previously unknown error of histidine metabolism (1 case).

Ammonia-Lyases↗