Premium
The oxygen reactive species of cytochrome‐ c ‐oxidase: An alternate view
Author(s) -
Brunori Maurizio,
Antonini Giovanni,
Malatesta Francesco,
Sarti Paolo,
Wilson Michael T.
Publication year - 1992
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(92)80972-j
Subject(s) - cytochrome c oxidase , cytochrome , cytochrome c , coenzyme q – cytochrome c reductase , chemistry , cytochrome c1 , electron transport chain , cytochrome c peroxidase , cytochrome p450 reductase , electron transport complex iv , oxygen , oxidase test , cytochrome b6f complex , cytochrome b , photochemistry , biochemistry , mitochondrion , enzyme , organic chemistry , mitochondrial dna , gene
In a recent review article Babcok and Wikström (Nature, 1992, 356, 301–309) proposed that the species of cytochrome‐ c ‐oxidase which binds molecular oxygen during turnover is the so‐called mixed valence enzyme, in which the binuclear center cytochrome a 3 ‐ Cu B is reduced, while the cytochrome a/Cu A sites are oxidized. This proposal is based on earlier work (Morgan and Wikström, Biochemistry 1991, 30, 948–958) in which it was found that the steady‐state reduction levels of cytochrome c and cytochrome a in respiring rat liver mitochondria (sustained by ascorbate and TMPD) are quite different, the latter being much more oxidized than the former; evaluation of the steady‐state reduction levels demanded a large correction due to the optical contribution of oxidized TMPD + which overlaps with the cytochromes. We report below that application of transient spectroscopy and SVD analysis to respiring rat heart myocytes, under conditions in which the contribution of TMPD + is very small or absent, allows to show that the steady‐state reduction levels of cytochrome c and cytochrome a are comparable at all times accessible to measurement in the rapid‐scanning stopped‐flow spectrophotometer. Our conclusion, in agreement with previous results, is that mixed valence cytochrome‐ c ‐oxidase as defined above is not the prevailing oxygen binding species of cytochrome‐ c ‐oxidase, unless electron donation to cytochrome c becomes rate limiting.