InterPro domain: IPR012846

Two groups of proteins form acetolactate from two molecules of pyruvate. The type of acetolactate synthase described in this entry also catalyzes the formation of acetohydroxybutyrate from pyruvate and 2-oxobutyrate, an early step in the branched chain amino acid biosynthesis; it is therefore also termed acetohydroxyacid synthase. In bacteria, this catalytic chain is associated with a smaller regulatory chain in an alpha2/beta2 heterotetramer. Acetolactate synthase is a thiamine pyrophosphate enzyme. In this type, FAD and Mg++ are also found. Several isozymes of this enzyme are found in Escherichia coli (strain K12), one of which contains a frameshift in the large subunit gene and is not expressed.