Enzyme derepression and feedback inhibition of the first enzyme are the regulatory mechanisms demonstrated for the tryptophan pathway in Saccharomyces cerevisiae. The relative contributions of the two mechanisms to the control of the flux through the pathway in vivo were analyzed by (i) measuring feedback inhibition of anthranilate synthase in vivo, (ii) determining the effect of regulatory mut...

Extracts of several microorganisms have been shown to possess tryptophan synthetase activity (2, 5, 6, 8, 9), i.e., such preparations, when incubated in buffer in the presence of indole, serine, and pyridoxal phosphate, catalyze a condensation of indole and serine with the concomitant production of an equivalent amount of tryptophan. Animals, which have a dietary requirement for tryptophan, app...