Patent ID: 7910342

Claim:
A method for conversion of acetolactate to dihydroxy-isovalerate comprising: a) providing a microbial host cell comprising a genetic construct encoding a polypeptide having ketol-acid reductoisomerase specific activity greater than 1.1 μmoles/min/mg wherein the genetic construct encoding a polypeptide having ketol-acid reductoisomerase activity is isolated from Pseudomonas or Vibrio ; and b) contacting the host cell of (a) with acetolactate wherein 2,3-dihydroxy-isovalerate is produced; wherein the ketol-acid reductoisomerase specific activity greater than 1.1 μmoles/min/mg is based on purified protein as measured by: A) NADPH consumption assay, run under the following conditions: i) pH of 7.5; ii) a temperature of 22.5° C.; and iii) a reaction buffer comprising a) 100 mM potassium-HEPES; b) 10 mM MgCl 2 ; c) 2.25 mM (R,S)-acetolactate; and d) 200 μM NADPH; and B) purified protein concentration as determined by absorbance at 280 nanometers.