Tryptophanase and tryptophan synthetase in Escherichia Coli

Abstract

The general objective of this study was to evaluate the effects of glucose and tryptophan in the induction or repression of the enzymes tryptophanase and tryptophan synthetase in Escherichia coli under different incubation time. In general, the tryptophanase activity expressed in the amount of indole produced was significantly higher in tubes with added L-tryptophan during the assay. It was also observed that tryptophanase activity has increased as the time of incubation increases. Cells B (grown in basal medium + DL-tryptophan) had the highest tryptophanse activity across time of incubation as compared with Cells A (basal medium only), Cells C (basal medium + glucose) and Cells D (basal medium + tryptophan + glucose). Cells C had the lowest tryptophanase activity followed by Cells D. The enzyme tryptophanase, which degrades tryptophan to indole, pyruvic acid and ammonia, is repressed by glucose. The inhibition by glucose and other carbohydrates of induced enzyme formation has been attributed to repression by intermediates of carbohydrate metabolism. It appeared that tubes without DL-serine had higher tryptophan synthetase activity or lower unutilized indole as compared with tubes with DL-serine. It was expected that higher synthetase activity should be present in tubes with DL-serine because together with indole, they served as reactants in the activity of the enzyme synthetase. There was also observed increase in tryptophan synthethase activity as the time of incubation was prolonged. Cells C had the highest tryptophan synthetase activity as compared to Cells A, Cells B and Cells D.