Enhancement of histidine and one-carbon metabolism in rats fed high levels of retinol.
(25/33)
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)
Roles of cysteine sulfinate and transaminase on in vitro dark reversion of urocanase in Pseudomonas putida.
(26/33)
Urocanase is inactivated in intact cells of Pseudomonas putida and photoactivated by brief exposure of the cells to the UV radiation in sunlight. The dark reversion (inactivation) in vitro is explained by the formation of a sulfite-NAD adduct. Our objective was to investigate the dark reversion in vivo. Various compounds were added to P. putida cells, and the reversion was measured, after sonication, by comparison of the activity before and after UV irradiation. Sulfite, cysteine sulfinate, and hypotaurine enhanced the reversion of urocanase in resting cells. The reversion was time and concentration dependent. Sulfite modified the purified enzyme, but cysteine sulfinate and hypotaurine could not, indicating that those two substances had to be metabolized to support the reversion. Both of those compounds yielded sulfite when they were incubated with cells. Transaminases form sulfite from cysteine sulfinate. P. putida extract contained a transaminase whose activity involved as alpha-keto acid and either cysteine sulfinate or hypotaurine for (i) production of sulfite, (ii) disappearance of substrates, (iii) formation of corresponding amino acids, and (iv) urocanase reversion. Porcine crystalline transaminase caused reversion of highly purified P. putida urocanase with cysteine sulfinate and alpha-ketoglutarate. We conclude that in P. putida cysteine sulfinate or hypotaurine is catabolized in vivo by a transaminase reaction to sulfite, which modifies urocanase to a form that can be photoactivated. We suggest that this photoregulatory process is natural because it occurs in cells with the aid of sunlight and cellular metabolism. (+info)
Histidine dissimilation in Streptomyces coelicolor.
(27/33)
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. (+info)
Regulation of hut enzymes and intracellular protease activities in Vibrio alginolyticus hut mutants.
(28/33)
The production of alkaline protease, collagenase and histidine utilization (Hut) enzymes by Vibrio alginolyticus wild-type, hutH1 and hutU1 strains was investigated. Alkaline protease synthesis was stimulated by histidine and urocanic acid in the wild-type and hutU1 strains. The hutH1 mutant alkaline protease production was stimulated by urocanic acid and not by histidine. The Hut enzymes in the wild-type strain were coordinately induced by histidine. Urocanase and formimino-hydrolase were induced by histidine in the hutH1 mutant which lacked histidase and was not able to convert histidine to urocanic acid. Collagenase production in peptone medium was inhibited in the hut mutants. It is concluded that in V. alginolyticus urocanic acid regulates alkaline protease synthesis but that the Hut enzymes are induced by histidine. The involvement of the Hut genetic system in the regulation of alkaline protease and collagenase synthesis is discussed. (+info)
Effect of methionine on in vivo histidine metabolism in rats.
(29/33)
Experiments were conducted to examine the effects of methionine supplementation on histidine metabolism in rats. All animals were fed 10% casein diets with a methionine content of either 0.6 or 1.1%. Experiments in which the animals were fed their diets containing an additional 1% histidine ad libitum for at least 10 days revealed that methionine-supplemented animals had a 49% reduction of plasma histidine and an 80% reduction in urinary excretion of formiminoglutamic acid (FIGLU) on day 10. This effect was not observed on day 5. In subsequent experiments rats were fed the control or test diet ad libitum prior to receiving their diets, containing a histidine load, by force-feeding. When a 100-mg histidine load was given on day 5, 24-hour urinary FIGLU excretion was 83% lower in methionine-supplemented animals. When rats were force-fed a 75-mg [ring-2-14C]histidine load on day 10, those receiving supplemental methionine oxidized 21% more of the histidine label to 14CO2 and excreted 61% less of the dose as urinary FIGLU in 24 hours. The activities of histidase and urocanase were unaffected by the methionine supplement. The results suggest that dietary methionine supplementation enhances the in vivo catabolism of histidine by stimulating one-carbon metabolism. Delivery of the methionine supplement by ad libitum feeding requires at least 5 days for this effect to be achieved. (+info)
The effect of nitrogen limitation on catabolite repression of amidase, histidase and urocanase in Pseudomonas aeruginosa.
(30/33)
In Pseudomonas aeruginosa, the synthesis of histidase, urocanase and amidase is severly repressed when succinate is added to a culture growing in pyruvate + ammonium salts medium. When growth is nitrogen-limited, catabolite repression by succinate of histidase and urocanase synthesis does not occur but succinate repression of amidase synthesis persists. Amidase synthesis is not regulated in the same way as histidase synthesis by the availability of other nitrogen compounds for growth. Growth of P. aeruginosa strain PACI in succinate + histidine media is nitrogen-limited since this strain is defective in a histidine transport system. When methyl-ammonium chloride is added to succinate + histidine media, growth inhibition occurs. Mutants isolated from succinate + histidine + methylammonium chloride plates were found to be resistant to catabolite repression by succinate even in ammonium salts media. It is suggested that the hut genes of P. aeruginosa may be regulated in the same way as in Klebsiella aerogenes, by induction by urocanate and activation by either the cyclic AMP-dependent activator protein or by glutamine synthetase. (+info)
Cloning and sequencing of a 29 kb region of the Bacillus subtilis genome containing the hut and wapA loci.
(31/33)
Within the framework of an international project for the sequencing of the entire Bacillus subtilis genome, a 29 kb chromosome segment, which contains the hut operon (335 degrees) and the wapA gene, has been cloned and sequenced. This region (28,954 bp) contains 21 complete ORFs and one partial one. The 5th, 6th and 17th genes correspond to hutH encoding histidase, hutP encoding the positive regulator for the hut operon and wapA encoding a precursor of three major wall-associated proteins, respectively. A homology search for their products deduced from the 21 complete ORFs revealed that nine of them exhibit significant homology to known proteins such as urocanase (Pseudomonas putida), a protein involved in clavulanic acid biosynthesis (Streptomyces griseus), amino acid permeases (lysine, Escherichia coli; histidine, Saccharomyces cerevisiae; and others), beta-glucoside-specific phosphotransferases (E. coli and Erwinia chrysanthemi) and 6-phospho-beta-glucosidases (E. coli and Erw. chrysanthemi). Based on the features of the determined sequence and the results of the homology search, as well as on genetic data and sequence of the hut genes reported by other groups, it is predicted that the B. subtilis hut operon may consist of the following six genes (6th-1st), the last of which is followed by a typical rho-independent transcription terminator: hutP, hutH, EE57A (hutU) encoding urocanase, EE57B (hutI) encoding imidazolone-5-propionate hydrolase, EE57C (hutG) encoding formiminoglutamate hydrolase and EE57D (tentatively designated as hutM) possibly encoding histidine permease. Interestingly, the direction of transcription of these hut genes is opposite to that of the movement of the replication fork. (+info)
Cloning, expression and mutational analysis of the urocanase gene (hutU) from Pseudomonas putida.
(32/33)
The histidine-utilizing hutU gene was isolated from a lambda-EMBL3 phage of a genomic library from Pseudomonas putida nicII and subcloned into the expression vector pT7-7. Escherichia coli BL21 cells were transformed with the recombinant plasmid and produced a catalytically active protein, amounting to approximately 30% of the total protein in the crude cell-free extract. The addition of NAD+ to the growth medium ensured the full occupation of active sites by the cofactor. This requires a mechanism for the transport of NAD+ into E. coli cells. Using the overproducing mutant a new, fast and efficient isolation procedure is described which yields electrophoretically homogeneous urocanase within two days. The yield of pure enzyme, based on the culture volume, has been improved 50-80-fold compared with the traditional method. To investigate the possible role of cysteine residues in the catalysis or in the tight binding of the cofactor NAD+, six different mutants were prepared. In each mutant protein, one conserved cysteine was exchanged for alanine. The resulting clones were tested for the expression of urocanase with catalytic activity; the Km and Vmax values were determined. Only Cys410 was essential for catalysis. There was no detectable reconstitution or increase of activity after the addition of NAD+, either in the essential Cys/Ala mutant or the other mutant proteins. Electrospray-mass spectroscopy of the wild-type enzyme revealed that the coenzyme is not covalently bound to the protein and computational analysis showed no typical sequence for a mononucleotide-binding domain like the Rossman fold. To obtain urocanase apoenzyme, P. putida nicII was transformed with pGP1-2 and pTET7-U and grown in nicotinate-depleted medium. Like the mutant proteins, no activation of the apoform occurred after the addition of NAD+. These observations led us to postulate a new model for the non-covalent but tight binding of NAD+ to the enzyme by 'trapping' the cofactor while folding the nascent protein. (+info)