Evidence for water as the product for oxygen reduction by cytochrome cd.

Evidence is presented that water is the final product of electron donation to molecular oxygen by cytochrome cd from Paracoccus denitrificans when ferrocytochrome c acts as donor to cd . Negative evidence for the accumulation of superoxide and peroxide was obtained by rate effect experiments in the presence of superoxide dismutase, catalase, and peroxidase. Positive evidence for water was obtained by showing a 4 to 1 stoichiometric balance for rates of electron acceptance from ferrocytochrome c to rates of donation to molecular oxygen.