Reaction of formiminoglutamate with liver glutamate dehydrogenase.
1. Kinetic aspects of the reaction between crystalline bovine liver glutamate dehydrogenase and formiminoglutamate were investigated to establish the conditions under which the latter may interfere with the assay of glutamate by using glutamate dehydrogenase and to explain why formiminoglutamate accumulates in vivo after histidine loading, although it can react with glutamate dehydrogenase. The Km and Vmax. values were compared with those of the enzyme reacting with glutamate. At pH 7.4 Km for formiminoglutamate was much higher and Vmax. much lower than the values for glutamate. 2. The equilibrium constant at pH 7.0 was 0.017 micrometer with formiminoglutamate, i.e. about one two-hundredths that with glutamate. 3. In vivo the interaction between glutamate dehydrogenase and formiminoglutamate is minimal even when the concentration of the latter in the liver is greatly raised, as in cobalamine or folate deficiency after histidine loading. 4. At pH 9.3, i.e. under the conditions for the assay of glutamate by glutamate dehydrogenase, formiminoglutamate reacts readily with the enzyme. (+info)
Gene order of the histidine utilization (hut) operons in Klebsiella aerogenes.
P1-sensitive mutants of Klebsiella aerogenes were isolated and the gene order of the hut region was then determined using P1-mediated transduction. The genes are located in the Klebsiella chromosome between gal and bio as in Salmonella typhimurium. The gene order, gal, hutI, hutG, hutC, huU, hutH, bio is also the same as that observed in S. typhimurium. (+info)
Vitamin B-12 and folate function in chronic alcoholic men with peripheral neuropathy and encephalopathy.
Forty-six male alcoholics hospitalized with polyneuropathy or intellectual impairment were studied after at least 2 wk of alcohol abstention. Neurological evaluation included neurophysiological examination of the sural nerve and tibial nerve, neurophysiological examinations, and CT-scanning of the brain. Alcohol and vitamin intakes were quantified by the interview method. Vitamin B-12 and folate status included examinations of peripheral blood and bone marrow aspirate, plasma vitamin B-12, plasma and erythrocyte folate, formiminoglutamic acid excretion test (FiGlu), methylmalonic acid excretion, and deoxyuridine suppression test (dU) on phytohemagglutinin-stimulated peripheral lymphocytes. The liver function was assessed by galactose elimination capacity and plasma clearance of antipyrine. There was no hematological sign of folate or vitamin B-12 deficiency. About 8% had low plasma folate, while neither erythrocyte folate nor plasma vitamin B-12 were decreased. However, half of the patients had functional folate deficiency as determined by abnormal FiGlu or dU. Compared to the remaining patients, those with abnormal FiGlu or dU had significantly more abnormal neurophysiological tests, and lower folate intake. There was no correlation between FiGlu or dU and the quantitative liver function tests. It is concluded that 1) folate deficiency may contribute to the development of alcoholic polyneuropathy, 2) the classical parameters for folate deficiency (blood concentrations, peripheral blood, and bone marrow examinations) are not reliable in diagnosing folate deficiency and 3) functional tests like FiGlu and dU are necessary to diagnose folate deficiency in alcoholics. (+info)
Folate deficiency in rats fed diets containing free amino acids or intact proteins.
Development of folate deficiency (FD) was evaluated in weanling rats fed diets containing mixtures of free amino acids or of vitamin-free casein and gelatin as sources of dietary nitrogen. FD could be produced in 21 d with amino acid diets that promoted maximum growth rate, were completely devoid of folate and contained 1% succinylsulfathiazole. Growth retardation and blood dyscrasia associated with FD could not be demonstrated in rats fed diets containing casein and gelatin as nitrogen sources because the vitamin-free casein contained low but measurable levels of folate. The most effective protocol to produce experimental FD in rats is to feed a folate-free diet that otherwise supports maximum growth in young animals. Additional modifications such as use of methotrexate or amino acid-imbalanced or protein-deficient diets are unnecessary. (+info)
Inhibitory effects of histidine and their reversal. The roles of pyruvate carboxylase and N10-formyltetrahydrofolate dehydrogenase.
1. N10-Formyltetrahydrofolate dehydrogenase was purified to homogeneity from rat liver with a specific activity of 0.7--0.8 unit/mg at 25 degrees C. The enzyme is a tetramer (Mw = 413,000) composed of four similar, if not identical, substrate addition and give the Km values as 4.5 micron [(-)-N10-formyltetrahydrofolate] and 0.92 micron (NADP+) at pH 7.0. Tetrahydrofolate acts as a potent product inhibitor [Ki = 7 micron for the (-)-isomer] which is competitive with respect to N10-formyltetrahydrofolate and non-competitive with respect to NADP+. 3. Product inhibition by NADPH could not be demonstrated. This coenzyme activates N10-formyltetrahydrofolate dehydrogenase when added at concentrations, and in a ratio with NADP+, consistent with those present in rat liver in vivo. No effect of methionine, ethionine or their S-adenosyl derivatives could be demonstrated on the activity of the enzyme. 4. Hydrolysis of N10-formyltetrahydrofolate is catalysed by rat liver N10-formyltetrahydrofolate dehydrogenase at 21% of the rate of CO2 formation based on comparison of apparent Vmax. values. The Km for (-)-N10-folate is a non-competitive inhibitor of this reaction with respect to N10-formyltetrahydrofolate, with a mean Ki of 21.5 micron for the (-)-isomer. NAD+ increases the maximal rate of N10-formyltetrahydrofolate hydrolysis without affecting the Km for this substrate and decreases inhibition by tetrahydrofolate. The activator constant for NAD+ is obtained as 0.35 mM. 5. Formiminoglutamate, a product of liver histidine metabolism which accumulates in conditions of excess histidine load, is a potent inhibitor of rat liver pyruvate carboxylase, with 50% inhibition being observed at a concentration of 2.8 mM, but has no detectable effect on the activity of rat liver cytosol phosphoenolpyruvate carboxykinase measured in the direction of oxaloacetate synthesis. We propose that the observed inhibition of pyruvate carboxylase by formiminoglutamate may account in part for the toxic effect of excess histidine. (+info)
Expression of the hut operons of Salmonella typhimurium in Klebsiella aerogenes and in Escherichia coli.
The normal hut (histidine utilization) operons, as well as those with mutations affecting the regulation of their expression, of Salmonella typhimurium were introduced on an F' episome into cells of S. typhimurium and Klebsiella aerogenes whose chromosomal hut genes had been deleted and into cells of Escherichia coli, whose chromosome does not carry hut genes. The episomal hut operons respond in a manner very similar to induction and catabolite repression in all three organisms. The small differences found reflect both different abilities to take up inducers from the medium and different degrees of catabolite repression exerted by glucose. (+info)
Regulation of the hut operons of Salmonella typhimurium and Klebsiella aerogenes by the heterologous hut repressors.
In merodiploid strains of Klebsiella aerogenes with chromosomal hut genes of K. aerogenes and episomal hut genes of Salmonella typhimurium, the repressor of either species can regulate the hut operons of the other species. The repression exerted by the homologous repressor on the left-hand hut operon is, in both organisms, stronger than that exerted by the heterologous repressor. (+info)
Enhancement of histidine and one-carbon metabolism in rats fed high levels of retinol.
Histidine metabolism was studied in rats fed 10% casein diets supplemented with 1000 IU of retinol/g concurrent with or previous to exposure to high levels of dietary histidine (1% or 2%). When a retinol-supplemented 10% casein + 1% histidine diet was fed ad libitum for 21 days, urinary excretion of formiminoglutamic acid (FIGLU) was decreased by 50-70% over the entire period and plasma histidine was reduced by 30-70% for 16 days compared to rats receiving 10% casein + 1% histidine with normal levels of retinol. Rats pretreated for 10 days with a 10% casein diet supplemented with high levels of retinol oxidized 30% more L-[ring-2-14C]histidine to 14CO2 and excreted 76% less of the administered dose as urinary FIGLU compared to control rats not pretreated with high levels of retinol. Depression in growth due to supplementation of a 10% casein diet with 1% histidine were also partially alleviated in rats that were first pretreated with retinol. Activities of histidase, urocanase, and formiminoglutamic acid formiminotransferase (FIGLU transferase) were unaffected by retinol supplementation. The results suggest that retinol supplementation enhances histidine catabolism by exerting a change on one-carbon metabolism. (+info)