1887

Abstract

SUMMARY: Valine dehydrogenase (VDH) from A3(2) was purified from cell-free extracts to apparent homogeneity. The enzyme had an 41000 in denaturing conditions and an 70000 by gel filtration chromatography, indicating that it is composed of two identical subunits. It oxidized L-valine and L-α-aminobutyric acid efficiently, L-isoleucine and L-leucine less efficiently, and did not act on D-valine. It required NAD as cofactor and could not use NADP. Maximum dehydrogenase activity with valine was at pH 10.5 and the maximum reductive amination activity with 2-oxoisovaleric acid and NHCl was at pH 9. The enzyme exhibited substrate inhibition in the forward direction and a kinetic pattern with NAD that was consistent with a sequential ordered mechanism with non-competitive inhibition by valine. The following Michaelis constants were calculated from these data: L-valine, 10.0 mM; NAD, 0.17 mM; 2-oxoisovalerate, 0.6 mM; and NADH, 0.093 mM. In minimal medium, VDH activity was repressed in the presence of glucose and NH , or glycerol and NH or asparagine, and was induced by D- and L-valine. The time required for full induction was about 24 h and the level of induction was 2- to 23-fold.

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/content/journal/micro/10.1099/00221287-136-2-273
1990-02-01
2019-11-17
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http://instance.metastore.ingenta.com/content/journal/micro/10.1099/00221287-136-2-273
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