Effect of ammonia on nitrogen fixation by the blue-green alga Anabaena cylindrica |
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Authors: | Ohmori, Masayuki Hattori, Akihiko |
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Affiliation: | Ocean Research Institute, University of Tokyo Nakano, Tokyo 164, Japan |
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Abstract: | Ammonia at a concentration of 1 ? 103M completely inhibitednitrogenase activity, as measured by acetylene reduction, inthe blue-green alga Anabaena cylindrica. Free ammonia was undetectablein cells grown either on N2 or ammonia within the limits ofprecision of the method used. Glutamic acid formed a major aminoacid pool in N2-grown cells, and basic amino acids, i.e. lysine,histidine and arginine were abundant in ammonia-grown cells.A 10-fold increase in the amounts of labile amino compound(s)was observed when N2-grown cells were exposed to ammonia. When cells were incubated under anaerobic conditions, the acetylene-reducingactivity increased 2-fold or more; ammonia had no effect. Oxygenwas required for ammonia to inhibit acetylene reduction. Modes of inhibition by ammonia on acetylene reduction were comparedwith those by chloramphenicol, puromycin, cycloheximide, DCMUand CCCP. On the basis of these comparisons we concluded thatammonia not only acts as a suppressor of nitrogenase synthesisbut also inhibits acetylene-reducing activity by lowering thesupply of reductant and/or of energy for the nitrogenase system. 1This work was supported by grant No. 38814 from the Ministryof Education. (Received July 30, 1973; ) |
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