Abstract

Tryptophan synthetase of Pseudomonas aeruginosa has a different optimum pH value in different buffer systems. In the phosphate buffer system, the optimum pH value was 7.4 and in tris, 7.9. The maximum reaction velocity was higher in phosphate buffer than in tris. The reaction velocity was found to be proportional to incubation time over a period of twenty minutes, and to the protein concentration in a range of 0 to 600μg per tube. The enzyme can carry on the reaction at a very low concentration of coenzyme pyridoxal phosphate (1x10^-8 M). The Km for serine was 2.0x10^-3 M and that for indole was 1.25x10^-3 M. The concentration of serine (3.7x10^-2 M) used in experiment had reached the saturation point while that of indole (1.25x10^-4 M) had not. The enzyme level of tryptophan synthetase was repressed by the addition of tryptophan, indole and anthranilate. At the same concentration (20μg/ml), indole and anthranilate had a greater repression effect on tryptophan synthetase than tryptophan did. The four analogues used in the experiment, 5-methyl tryptophan, 6-methyl tryptophan, indolepropionic acid and indoleacrylic acid, did not have any apparent effect on the growth of Pseudomonas aeruginosa. However, they showed repression on the enzyme level of tryptophan synthetase when they were added to the growth medium.