Induction and modification of dinitrogenase reductase in the unicellular cyanobacterium Synechocystis BO 8402

Oxygen is an important regulatory factor of nitrogenase induced in a unicellular cyanobacterium, Synechocystis BO 8402, during nitrogen starvation. Synthesis of the enzyme is limited by the efficiency of the cells to remove oxygen by respiration, supported by hydrogenases and, in the light, by inhibition of photosynthesis. With a polyclonal antibody against dinitrogenase reductase (the Fe protein of nitrogenase) a single polypeptide is detected, indicative of an active dimeric enzyme in dense cell suspensions. Inhibition of nitrogenase by addition of oxygen is accompanied by the appearance of a second polypeptide of the Fe protein having a 1.5 kDa higher molecular weight. This disappears upon removal of oxygen from the gas phase while nitrogenase activity is restored. No protein synthesis is required indicating that a fraction of the existing polypeptides is reversibly modified in response to oxygen. After induction of nitrogenase activity in dilute culture suspensions, both forms of the Fe-protein are found in variable amounts possibly due to oxygen contamination during the experiment.Abbreviations CAM chloramphenicol - Chl chlorophyll a - CHO carbohydrates - DCMU 3,4-dichlorophenyl-1,1-dimethylurea (diuron) - kDa kilodalton - SDS sodium dodecylsulphate