ENDOGENOUS AMMONIA PRODUCTION BY ANACYSTIS-NIDULANS R-2 INDUCED BY METHIONINE SULFOXIMINE

A. nidulans R-2 produced ammonia from endogenous sources for at least 6 h when illuminated without external N source but with CO2 in the presence of 50 .mu.M methionine sulfoximine. The onset of ammonia release coinciding with complete inhibition of glutamine synthetase. The total quantity of ammonia which could be released exceeded the N content of small molecule pools, and suggested protein degradation as the most likely source of the N. Ammonia release was not accompanied by leakage of C compounds from the cells. Methionine sulfoximine-induced ammonia release was energy requiring, and was barely detectable under dark anaerobic conditions, or in the presence of 10 .mu.M carbonyl cyanide m-chlorophenylhydrazone in light. Phenyl methyl sulfonylfluoride, an inhibitor of serine proteases, eliminated ammonia release, and the rate of release was reduced to 1/3 of control values, after a lag, in the presence of 50-75 .mu.g/ml chloramphenicol. The rate of NH4+ release was maximal (1.4 mmol .cntdot. min-1 .cntdot. mg-1 protein) if suspensions were bubbled with 100% O2, but could not be reduced below 0.6 nmol .cntdot. min-1 mg-1 protein in air: CO2, suggesting that release was at most only partly due to photorespiration.