Purification and characterization of the indole‐3‐glycerolphosphate synthase/anthranilate synthase complex of Saccharomyces cerevisiae

The indole‐3‐glycerolphosphate synthase/anthranilate synthase complex from Saccharomyces cerevisiae was purified to apparent homogeneity. The native complex with M r ∼ 130000 consists of two different subunits, the TRP2 gene product with M r = 64000 and the TRP3 gene product with M r = 58000. The larger polypeptide was identified as anthranilate synthase and is active in vitro with ammonia as cosubstrate without need of complex formation. The smaller polypeptide carries both glutamine amidotransferase activity and indole‐3‐glycerolphosphate synthase activity. Various steady‐state kinetic parameters as well as the amino acid composition of the two polypeptides were determined.