The cell-free extract was prepared from a halo-tolerant Micrococcus (strain no. 203) by phosphate buffer extraction at pH 6.8 in the presence of 0.3[image] NaCl, acetone precipitation, and resuspension the enzyme system by ultrasonic oscillation. This preparation was rich in cytochrome b4, but not in other cytochromes, and catalyzed the reduction of nitrite to N2 in the presence of the following electron donors: reduced methylene blue, reduced phenazine methosulfate, ferrocytochrome b4, succinate-succinic dehydrogenase system, and upon the addition of flavine adenine dinucleotide, reduced diphospho-pyridine nucleotide or glucose-pyridine nucleotides system. Electron transport from cytochrome b4 to nitrite reductase was activated by the presence of high NaCl concentration. An electron transferring scheme in the cells is presented: pyridine nucleotides [forward arrow] flavoproteins [forward arrow] vitamin K [forward arrow] Antimycin A sensitive factor [forward arrow] cytochrome b4 [forward arrow] unidentified factor, which can be linked to succinate dehydrogenase system [forward arrow] unknown factor, which reacts with leucomethylene-blue [forward arrow] nitrite reductase. Phenazine methosulfate is directly linked to nitrite reductase. The nitrite reductase was inhibited by CO, azide, cyanide and some metal-chelating agents.