Studies in valine biosynthesis: II. Enzymatic dehydration of α,β-dihydroxyisovaleric acid by plant extracts

Abstract

An enzyme that catalyzes the dehydration of [alpha],[beta]-dihydroxyisovaleric acid to a keto acid, presumably [alpha]-ketoisovaleric acid, was found in extracts of Chlorella pyrenoidosa and higher plants. Keto acid formation, as measured by a dinitrophenylhydrazone extraction procedure, occurred as readily in a N2 gas phase as in air or O2 atmosphere, demonstrating the catalyzed reaction to be a splitting out of a molecule of water. The dehydrase assay was influenced in the usual enzymatic manner by heat denatura-tion, enzyme concentration and length of time of reaction. The enzyme was soluble after centrifugation of extracts at 70,000 x G. For both seedlings and adult plants the dehydrase was found primarily in the leaves and had a widespread distribution (29 genus in 14 angiosperm families). A possible function of this dlhydroxy acid dehydrase in valine biosynthesis is described.[long dash]Auth. abst.