AEROBIC AND ANAEROBIC RESPIRATION IN MICROCOCCUS DENITRIFICANS

The adaptive formation of nitrate and nitrite reductases in Micrococcus denitrificans as well as the properties and the relation between the NO3- and O2 respiratory pathways have been investigated. 1. 1. Nitrate and nitrite reductases which are induced by their substrates are repressed by O2. 2. 2. Increased amounts of cytochromes b and c and a haemprotein (absorption at 465, 650-680 mμ) were found in cells grown anaerobically with NO3- or NO2-. 3. 3. Cytochrome-oxidase activity was higher in anaerobically grown cells but NADH oxidase was similar in cells grown with or without air. 4. 4. NO3-, NO2- and O2 serve as electron acceptors when lactate, malate, NADH, NADPH and succinate are the donors. 5. 5. O2 and NO2- oxidise all cytochromes in the respiratory chain whereas with a limited concentration of NO3- cytochrome b was primarily oxidised. 6. 6. NADH oxidase, succinate oxidase and nitrite reductase were inhibited by antimycin A and 2-n-heptyl-4-hydroxyquinoline-N-oxide. These enzymes and nitrate reductase were also inhibited by KCN, amytal, mepacrine, pericidine A and by rotenone when NADH only was the electron donor. 7. 7. NADH oxidase and cytochrome c oxidase in extracts from anaerobically grown cells were strongly inhibited by NO2- but NADH oxidase only was affected by NO3-. NO3- and NO2- did not affect the same enzymes from cells grown in air. 8. 8. Nitrate reductase was unaffected by O2 but nitrite-reductase activity was strongly inhibited. © 1969.