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At least 397 records · Page 22Linked to original sources
PubMed1991

On kynureninase activity.

1) In Mg-deficient rats, kynureninase activity is decreased. 2) p-Hydroxyphenylpyruvate inhibits kynureninase activity. 3) -SH groups in the apoenzyme of kynureninase play a very important role in the enzymatic reaction. 4) 3-Hydroxykynurenine may be a very important regulative metabolite in the 3-hydroxykynurenine----xanthurenic acid pathway.

Animals↗
PubMed1982

Chorismate mutase-prephenate dehydrogenase from Escherichia coli. Kinetic mechanism of the prephenate dehydrogenase reaction.

The mechanism of the dehydrogenase reaction catalyzed by chorismate mutase-prephenate dehydrogenase (chorismate pyruvatemutase, EC 5.4.99.5-prephenate:NAD+ oxidoreductase (decarboxylating), EC 1.3.1.12) has been investigated using steady-state kinetic techniques. The steady-state velocity pattern in the absence of products as well as product and dead-end inhibition patterns are consistent with a random mechanism in which two dead-end complexes, E-NADH-prephenate and E-NAD-hydroxyphenylpyruvate, are formed, and in which all steps are in rapid equilibrium except that concerned with the interconversion of central ternary complexes. Values have been determined for the maximum velocity of the reaction as well as for the kinetic parameters associated with the combination of substrates, products and the dead-end inhibitor, AMP, with various enzyme forms. The results indicate that when albumin is present in the reaction mixture, the presence of one substrate on the enzyme does not affect the combination of the second substrate. On the other hand, the binding of 4-hydroxyphenylpyruvate is enhanced by the presence of NAD and the binding of NADH is enhanced by the presence of prephenate on the enzyme. These results contrast with the finding that the inhibitory analogue, AMP, binds more strongly to the free enzyme than to the E-prephenate complex.

Adenosine Monophosphate↗
PubMed1982

Phenylalanine metabolism in Microtus montanus chronically infected with Trypanosoma brucei gambiense.

1. Alterations in phenylalanine metabolism were observed in Microtus montanus infected with Trypanosoma brucei gambiense. 2. Reductions were found in the incorporation of phenylalanine into free amino acid pools and into proteins of the liver and other organs of infected animals. 3. Increased quantities of phenylpyruvate, 4-hydroxyphenylpyruvate and pyruvate were found in the urine of infected Microtus. 4. There appeared to be very limited conversion of phenylalanine to tyrosine in infected animals. This suggested that either phenylalanine transaminase activity was greatly elevated in proportion to phenylalanine hydroxylase activity; or that phenylalanine hydroxylase activity was actually reduced during the infection.

Animals↗
PubMed2001

The Lly protein is essential for p-hydroxyphenylpyruvate dioxygenase activity in Legionella pneumophila.

The lly locus confers fluorescence, haemolysis, brown pigmentation and an increased resistance to light in Legionella pneumophila. In this study, we correlated the pigment production of two lly-positive L. pneumophila isolates and a recombinant lly-positive Escherichia coli strain with the presence of homogentisic acid (HGA) in the culture supernatant. The detection of HGA by high performance liquid chromatography and the data analysis of the deduced amino acid sequence of the lly gene indicate that the lly locus codes for a p-hydroxyphenylpyruvate dioxygenase (HPPD). This enzyme catalyses the transformation of p-hydroxyphenylpyruvate into HGA, which subsequently oxidises and polymerises into a melanin-like pigment. One open reading frame (ORF 1) in the lly region exhibited homologies with genes of Synechocystis sp., Petroselium crispum and Streptomyces mycarofaciens that code for methyltransferases. By screening a genomic library of L. pneumophila (serogroup 1) strain Corby with a monoclonal antibody against the legiolysin (lly), we identified two recombinant E. coli clones that did not produce the brown pigment and showed no haemolysis and fluorescence. DNA sequencing revealed that both clones contained 874 nucleotides of the N-terminal part of the lly gene. The recombinant strains expressed truncated legiolysin proteins of 39.5 and 35.7 kDa and did not produce HGA. Considering the highly conserved structure of legiolysin-like HPPD genes from other organisms, we suggest that the C-terminus of the legiolysin may be essential for the enzymatic activity that conferred pigmentation via HGA polymerisation, haemolysis and fluorescence.

4-Hydroxyphenylpyruvate Dioxygenase↗
PubMed1995

Characterization of the melanogenic system in Vibrio cholerae, ATCC 14035.

The nature of the pigment formed by Vibrio cholerae and the characterization of its biosynthetic pathway is shown. This microorganism is able to synthesize melanin-like pigment when cultured in the presence of L-tyrosine. Other phenolic chemicals related to L-tyrosine do not lead to pigment production. The microorganism has no tyrosine hydroxylase activity, and the levels of dopa oxidase activity are very low, making the existence of a tyrosinase very unlikely. However, Vibrio cholerae contained transaminases that transforms L-tyrosine into p-hydroxyphenylpyruvate. Moreover, Vibrio cholerae is able to go further in the catabolic pathway, releasing a great amount of homogentisic acid. This acid can spontaneously be oxidized to its p-quinone form, which subsequently polymerizes leading to pigment formation. It is concluded that the pigment formed by Vibrio cholerae is not synthesized by the Raper-Mason pathway, but by a L-tyrosine catabolism pathway leading to homogentisic acid. Some simple properties of that melanin are compared to model eu- and pheomelanin, but no clear distinction could be stated, indicating the similarity between all these pigments.

Chromatography, High Pressure Liquid↗
PubMed1983

Effects of dietary protein level and ascorbic acid supplementation on the contents of tyrosine metabolites in droppings and plasma of chicks fed a diet containing excess tyrosine.

A study on chickens was conducted to investigate whether or not: a) excess dietary tyrosine increases the content of tyrosine metabolites in plasma and excreta, b) these elevations of tyrosine metabolites are presented by increasing dietary protein level or supplementing with ascorbic acid (AA), and c) urine is a major excretory route of tyrosine metabolites. Chicks fed a 10% protein diet with excess tyrosine developed external foot lesions accompanied by retarded growth and depressed feed intake. These adverse effects were alleviated by elevating dietary protein level or supplementing with AA. Excreta and plasma of chicks fed the 10% protein diet contained small or undetectable amounts of free tyrosine, 4-hydroxyphenylpyruvate (4-HPP), 4-hydroxyphenylacetate (4-HPL), and 4-hydroxyphenylacetate (4-HPA), while these metabolites were markedly increased by the addition of excess tyrosine to the 10% protein diet. From the results with colostomized cocks, the major source of 4-HPP, 4-HPL, and 4-HPA excreted by chicks fed a tyrosine excess diet was considered more likely to be of urinary than fecal origin. Elevated contents of tyrosine and its metabolites in plasma were partially counteracted by increasing dietary protein level or AA supplementation. In excreta, elevated contents of tyrosine and its metabolites caused by excess tyrosine were reduced by increasing dietary protein level and supplementing with AA when expressed in the proportion of tyrosine intake. These results suggest that the beneficial effects of increased dietary protein level and supplementation with AA are related to enhanced ability of chicks to degrade excessively ingested tyrosine.

Animals↗
PubMed1975

Phenylalanine hydroxylase from Pseudomonas sp. (ATCC 11299a). Purification, molecular weight, and influence of tyrosine metabolites on activation and hydroxylation.

Phenylalanine hydroxylase from Pseudomonas sp. (ATCC 11299a) has been purified 25- to 30-fold by a procedure which has been modified from that previously described for this organism (Guroff, G., and Ito, T. (1965) J. Biol. Chem. 240, 1175-1184; Guroff, G., and Rhoads, C. A. (1967) J. Biol. Chem. 242, 3641-3645). Further purification yielded a preparation which was judged to be about 80% pure by sodium dodecyl sulfate-containing and standard analytical polyacrylamide gels, but the activity in this preparation has proved to be very labile. The enzyme appears to be a single protein chain of between 25,000 to 27,000 molecular weight. Phenylalanine, tyrosine, and tryptophan inhibit the activation of the enzyme by iron in a competitive fashion. The tyrosine metabolites, p-hydroxyphenylpyruvic and homogentisic acids exhibit a biphasic effect on activation, stimulating at low iron, and inhibiting at higher iron concentrations. The hydroxylation itself is inhibited by tyrosine and related compounds such as L-3,4-dihydroxyphenylalanine and dopamine. p-Hydroxyphenylpyruvic acid is a competitive inhibitor with respect to both substrate and cofactor. The data indicate a variety of means by which the bacterium can regulate phenylalanine hydroxylation.

Enzyme Activation↗