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PubMed1978

Determination of 3-methoxy-4-hydroxyphenylpyruvic acid, 3,4-dihydroxyphenylethylene glycol, and 3,4-dihydroxyphenylmandelic acid in urine by mass fragmentography, with use of deuterium-labeled internal standards.

We report the determination of 3-methoxy-4-hydroxyphenylpyruvic acid, 3,4-dihydroxyphenylmandelic acid, and 3,4-dihydroxyphenylethylene glycol in urine, by use of gas chromatography/mass spectrometry in combination with a simple purification method and deuterium-labeled internal standards. Normal excretion values in terms of creatinine, expressed as a function of age, are given, together with results obtained for patients with neuroblastoma, pheochromocytoma, or parkinsonism treated with L-DOPA + peripheral decarboxylase inhibitor, and for a patient receiving dopamine. We were unable to identify 3, 4-dihydroxyphenyllactic acid in urine. The results obtained and their relation to other catecholamine metabolites and catecholamine-precursor metabolites in urine are discussed.

Adolescent↗
PubMed1995

X-ray structure of two complexes of the Y143F flavocytochrome b2 mutant crystallized in the presence of lactate or phenyl lactate.

Flavocytochrome b2 is a flavohemo enzyme localized in the intermembrane space of yeast mitochondria, where it catalyzes the electron transfer from its substrate, L-lactate, to cytochrome c. We have obtained crystals of a flavocytochrome b2 mutant, Y143F, which are isostructural with those of the native recombinant enzyme [Tegoni, M., & Cambillau, C. (1994) Protein Sci.3, 303-314]. These crystals were grown under similar conditions to those used to obtain the recombinant enzyme, but in the presence of phenyl lactate or lactate. We report here on the structural analysis of the two complexes of flavocytochrome b2 with the reaction products at 2.9 A resolution. In both structures, the Phe143 phenyl ring keeps the same position as that of the phenolic ring of Tyr143 in both the native recombinant and in the native wild-type enzymes. The product of the reaction, phenyl pyruvate or pyruvate, is present at the active site of both subunits, and not only in subunit 2 as observed in the wild-type structure [Xia, Z.-X., & Mathews, F.S. (1990) J. Mol. Biol. 212, 837-863]. The number of interactions between the FMN and the heme domain is considerably lower in the Y143F mutant than in the native proteins. The latter finding strongly supports the hypothesis that the main role of Tyr143 in the native proteins. The latter findings strongly supports the hypothesis that the main role of Tyr143 in the native protein probably consists in establishing a hydrogen bond with the heme [Xia, Z.-X., & Mathews, F.S. (1990) J. Mol. Biol. 212, 837-863]. This interaction appears to be essential for the two domains to approach each other suitably so that the intramolecular electron transfer can occur.

Binding Sites↗
PubMed1973

Effect of phenylpyruvate on enzymes involved in fatty acid synthesis in rat brain.

1. The activities of, and the effects of phenylpyruvate on, citrate synthase (EC 4.1.3.7), acetyl-CoA carboxylase (EC 6.4.1.2) and fatty acid synthetase derived from the brains of 14-day-old and adult rats were investigated. 2. The brain citrate synthase from 14-day-old rats had a K(m) for oxaloacetate of 2.38mum and for acetyl-CoA of 16.9mum, and a V(max.) of 838nmol of acetyl-CoA incorporation/min per mg of mitochondrial protein. From adult rat brain this enzyme had a K(m) for oxaloacetate of 2.5mum and for acetyl-CoA of 16.6mum and a V(max.) of 1070nmol of acetyl-CoA incorporated/min per mg of mitochondrial protein. Phenylpyruvate inhibited the enzyme from adult and young rat brains in a competitive fashion with respect to acetyl-CoA, with a K(i) of 700mum. 3. The brain acetyl-CoA carboxylase from 14-day-old rats had a K(m) for acetyl-CoA of 21mum and a V(max.) of 0.248nmol/min per mg of protein, and from adult rats a K(m) for acetyl-CoA of 21mum and a V(max.) of 0.173nmol/min per mg of protein. The enzyme from young and adult rats required citrate (K(a)=3mm) for activation and were inhibited non-competitively by phenylpyruvate, with a K(i) of 10mm. 4. The brain fatty acid synthetase from 14-day-old rats had a K(m) for acetyl-CoA of 7.58mum and a V(max.) of 1.1 nmol of malonyl-CoA incorporated/min per mg of protein, and from adult rats a K(m) for acetyl-CoA of 4.9mum and a V(max.) of 0.48nmol of malonyl-CoA incorporated/min per mg of protein. Phenylpyruvate acted as a competitive inhibitor with respect to acetyl-CoA with a K(i) of 250mum for the enzyme from 14-day-old rats. 5. These results are discussed with respect to phenylketonuria, and it is suggested that the inhibition of the brain fatty acid synthetase and possibly the citrate synthetase by phenylpyruvate could explain the defective myelination characteristic of this condition.

Journal Article↗