Abstract

5-Fluorotryptophan, a strong inhibitor of Pseudomonas putida at a concentration of 200μg/ml, had an inhibitory effect on Pseudomonas aeruginosa(PA-1), but even at very high concentration the inhibition was still incomplete. On the other hand, another analogue, 5-fluoroindole, showed complete inhibitory effect on both PA-1 and P. putida at a concentration of 50μg/ml. Tryptophan, the end product of tryptophan biosynthetic pathway, showed a little feedback inhibition on tryptophan synthetase. And the inhibition was less effective on the analogue-resistant mutants: 5-FIR-12 and 5-FTR-1, than on the wild type. 5-Fluoroindole could be substituted for indole as the substrate of tryptophan synthetase. But 5-fluoroindole gave the enzyme a partially competitive inhibition with respect to serine. Whereas 5-fluorotryptophan showed inhibition on both substrates: indole and serine. The inhibitory effect was found to be proportional to the concentration of indole. And this analogue also exhibited a partially competitive inhibition with respect to serine. From the results, the conclusion can be drawn that 5-fluoroindole dose not inhibit PA-1 mainly by its conversion to 5-fluorotryptophan, but rather it may affect the cells directly or by its conversion to other strong inhibitors.