STUDIES ON NORMAL AND GENETICALLY ALTERED TRYPTOPHAN SYNTHETASE FROM NEUROSPORA CRASSA

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Abstract
Studies of the activities of wild type tryptophan synthetase indicate that it is responsible for the formation of indole as well as tryptophan. Evidence is presented that a single protein, tryptophan synthetase, is responsible for these three reactions: (1) indole + serine [forward arrow]itryptophan; (2) inGP + serine [forward arrow] tryptophan + triose phosphate; (3) inGPindole + triose phosphate; crude extracts from td 2 and td 71, examined for their ability to convert InGP to indole, showed that these mutants lost the ability to catalyze reactions (1) and (2) but retained their ability to catalyze reaction (3). Reaction (3) in these extracts is catalyzed by a protein CRM (cross reacting material) which is immunologically related to wild type tryptophan synthetase suggesting that the reaction is catalyzed by a mutationally altered tryptophan synthetase in these mutants. Reaction (3) in td 2 and td 71 requires pyridoxal phosphate and also serine in the case of td 71, representing new requirements for these altered enzymes. The CRM to enzyme activity ratio in td 71 extracts indicates an apparent increase in the rate of the reaction per unit of CRM activity.