Endogenous ammonia production by Anacystis nidulans R-2 induced by methionine sulfoximine |
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Authors: | Samy Boussiba X -Q Liu Jane Gibson |
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Institution: | (1) Section of Biochemistry, Molecular and Cell Biology, Division of Biological Sciences, Cornell University, 14853 Ithaca, NY, USA |
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Abstract: | Anacystis nidulans R-2 produced ammonia from endogenous sources for at least 6 h when illuminated without external nitrogen source but with CO2 in the presence of 50 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 nitrogen content of small molecule pools, and suggested protein degradation as the most likely source of the nitrogen. Ammonia release was not accompanied by leakage of carbon 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 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 one-third of control values, after a lag, in the presence of 50–75 g/ml chloramphenicol. The rate of NH
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release was maximal (1.4 nmol·min-1·mg-1 protein) if suspensions were bubbled with 100% O2, but could not be reduced below 0.6 nmol·min-1·mg-1 protein in air: CO2, suggesting that release was at most only partly due to photorespiration.Abbreviations used MSX
L-methionine D,L-sulfoximine
- PMSF
phenylmethylsulfonylfluoride
- CAP
chloramphenicol
- CCCP
carbonyl cyanide-m-chlorophenyl hydrazone |
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Keywords: | Ammonia production Protein breakdown Anacystis nidulans |
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