Enzymes of the tryptophan pathway in Acinetobacter calco-aceticus

All enzymes of the tryptophan synthetic pathway were detectable in extracts from wild-type Acinetobacter calco-aceticus. The levels of these enzymes were determined in extracts from a number of auxotrophs grown under limiting tryptophan. In each case only anthranilate synthetase was found to be present in increased amounts, whereas the specific activities of the remaining enzymes remained unchanged and unaffected by the tryptophan concentration. Derepression of anthranilate synthetase was found to occur as the concentration of tryptophan became limiting. Anthranilate synthetase and phosphoribosyl transferase activities are both feedback-inhibited by tryptophan. Molecular weight determination carried out by gel filtration and zonal centrifugation in sucrose revealed that all the enzymes are less than 100,000, and no molecular aggregates of these enzymes were detected. The data indicate that tryptophan synthesis in Acinetobacter is regulated both by feedback inhibition of the first two enzymes of the pathway and by repression control of anthranilate synthetase.