Aerobic and anaerobic respiration in Micrococcus denitrificans

Abstract

The adaptive formation of nitrate and nitrite reductases in Micrococcus denitrificans as well as the properties and the relation between the NO 3 − and O 2 respiratory pathways have been investigated. 1. 1. Nitrate and nitrite reductases which are induced by their substrates are repressed by O 2. 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 NO 3 − or NO 2 −. 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. NO 3 −, NO 2 − and O 2 serve as electron acceptors when lactate, malate, NADH, NADPH and succinate are the donors. 5. 5. O 2 and NO 2 − oxidise all cytochromes in the respiratory chain whereas with a limited concentration of NO 3 − 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 NO 2 − but NADH oxidase only was affected by NO 3 −. NO 3 − and NO 2 − did not affect the same enzymes from cells grown in air. 8. 8. Nitrate reductase was unaffected by O 2 but nitrite-reductase activity was strongly inhibited.