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

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Abstract
The indole-3-glycerolphosphate synthase/anthranilate synthase complex from Saccharomyces cerevisiae was purified to apparent homogeneity. The native complex with MW .simeq. 130,000 consists of 2 different subunits, the TRP2 gene product with MW = 64,000 and the TRP3 gene product with MW = 58,000. 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 aminotransferase activity and indole-3-glycerolphosphate synthase activity. Various steady-state kinetic parameters as well as the amino acid composition of the 2 polypeptides were determined.