H(+) + 2 pyruvate = (2S)-2-acetolactate + CO2 Optimum pH is 6. Polyol metabolism; (R,R)-butane-2,3-diol biosynthesis; (R,R)-butane-2,3-diol from pyruvate: step 1/3. Does not seem to require thiamine pyrophosphate. Valine resistant. Belongs to the TPP enzyme family.