acetolactate synthase, large subunit, biosynthetic type
Two groups of proteins form acetolactate from two molecules of pyruvate. The type of acetolactate synthase described in this model 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 E. coli K12, one of which contains a frameshift in the large subunit gene and is not expressed. [Amino acid biosynthesis, Pyruvate family]
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