Comparative study of the enzymatic synthesis of l-valine by purified enzymes, crude extract, intact or permeabilized cells from Bacillus megaterium

Abstract

A detailed study on the reductive amination of α-ketoisovalerate to l-valine by l-valine dehydrogenase using glucose dehydrogenase as an NADH regeneration enzyme was performed. The presence of both enzyme activities in Bacillus megaterium ATCC 39 118 permitted a direct and systematic comparison of the performances (initial l-valine production rate, productivity, molar conversion yield) of different types of conversion systems: purified enzymes or crude extract and whole cells, intact or permeabilized. A maximal l-valine productivity of 8 mmol·l−1 · h−1 was obtained using purified enzymes which constituted the most efficient system with a maximal rate of 0.87 μmol · ml−1 · min−1 and a molar conversion yield of 0.91. Permeabilized cells were also an attractive system because of their easy preparation and of the good performances attained.