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Effect of phenylpyruvate on mevalonate-activating enzymes from chick brain and liver.

Mevalonate-activating enzymes from chick brain and liver were stable when 105,000 x g supernatants were stored at -4 degrees C for 168 h. Mevalonate kinase and mevalonate 5-phosphate kinase retained their activities for 72 h at 4 degrees C while mevalonate 5-pyrophosphate decarboxylase activity significantly decreased after 24-48 h of storage at 4 degrees C. Direct addition of 2.5 mM phenylpyruvate to the reaction mixture produced a significant inhibition of decarboxylase activity in brain and liver. When enzyme preparations were preincubated with 2.5 mM phenylpyruvate for 20 min before the addition of substrate, an increased inhibition was observed. Mevalonate kinase and mevalonate 5-phosphate kinase from both tissues were not affected in the same conditions. The inhibition of brain and liver decarboxylase was progressive with increasing concentrations (2.5-10.0 mM) of phenylpyruvate. No significant difference was observed in the inhibition of decarboxylase after 10 or 20 min of preincubation.

Animals↗

Transamination of 3-phenylpyruvate in pancreatic B-cell mitochondria.

High aminotransferase activities catalyzing the reaction between L-glutamate and the aromatic ketomonocarboxylic acid, 3-phenylpyruvate, were observed in the mitochondria from pancreatic B-cells. At very low concentrations of 3-phenylpyruvate, L-glutamine was an effective amino group donor. The aminotransferase activities for the aliphatic ketomonocarboxylic acids, pyruvate and 2-ketoisovalerate, were lower in B-cell mitochondria. High rates of transamination of 2-ketoisocaproate with L-glutamine were observed and may be an important prerequisite for the insulin secretory potency of this 2-keto acid. Since B-cell mitochondria are well supplied with L-glutamine and L-glutamate, 3-phenylpyruvate-induced 2-ketoglutarate production may explain the insulin secretory potency of 3-phenylpyruvate which is not a fuel for pancreatic islet cells.

Animals↗

Enzymatic asymmetric synthesis by decarboxylases.

Decarboxylation reactions using microbial cells or enzymes are increasingly being used for the synthesis of enantiomerically pure compounds because of their high degree of regio- and stereo-specificity. Pyruvate decarboxylase, benzoylformate decarboxylase and phenylpyruvate decarboxylase enzymes are capable of acyloin-type condensation reactions leading to formation of chiral alpha-hydroxy ketones, which are versatile building blocks in the pharmaceutical and chemical industries. Availability of three-dimensional structures of some decarboxylases in recent years has facilitated understanding of reaction mechanisms and the creation of mutants with enhanced activity and stability.

Acetoacetates↗