Enzymatic removal of nitric oxide catalyzed by cytochrome c ' in Rhodobacter capsulatus

Cytochrome c' from Rhodobacter capsulatus has been shown to confer resistan ce to nitric oxide (NO). In this study, we demonstrated that the amount of cytochrome c' synthesized for buffering of NO is insufficient to account fo r the resistance to WO but that the cytochrome-dependent resistance mechani sm involves the catalytic breakdown of NO, under aerobic and anaerobic cond itions. Even under aerobic conditions, the NO removal is independent of mol ecular oxygen, suggesting cytochrome c' is a NO reductase, Indeed, we have measured the product of NO breakdown to be nitrous oxide (N2O), thus showin g that cytochrome c' is behaving as a NO reductase, The increased resistanc e to NO conferred by cytochrome c is distinct from the NO reductase pathway that is involved in denitrification, Cytochrome c' is not required for den itrification, but it has a role in the removal of externally supplied NO. C ytochrome c' synthesis occurs aerobically and anaerobically but is partly r epressed under denitrifying growth conditions when other NO removal systems are operative. The inhibition of respiratory oxidase activity of R, capsul atus by NO suggests that one role for cytochrome c' is to maintain oxidase activity when both NO and O-2 are present.