Acetohydroxy acid isomeroreductase catalyses the conversion of acetohydroxy acids into dihydroxy valerates. This reaction is the second in the synthetic pathway of the essential branched side chainamino acids valine and isoleucine [<cite idref="PUB00001302"/>]. The enzyme forms a tetramer of similar but non-identical chains, and requires magnesium as a cofactor. Acetohydroxy acid isomeroreductase C-terminal