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Flash‐induced membrane potential generation by cytochrome c oxidase
Author(s) -
Zaslavsky Dmitry,
Kaulen Andrey D.,
Smirnova Irma A.,
Vygodina Tatiana,
Konstantinov Alexander A.
Publication year - 1993
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(93)80843-j
Subject(s) - chemistry , protonation , electron transfer , microsecond , membrane potential , photochemistry , proton , cytochrome c oxidase , heme , cyanide , heme a , redox , stereochemistry , inorganic chemistry , ion , biochemistry , organic chemistry , enzyme , physics , quantum mechanics , astronomy
Flash‐induced single‐electron reduction of cytochrome c oxidase. Compound F (oxoferryl state) by Ru II (2,2'‐bipyridyl) 2+ 3 [Nilsson (1992) Proc. Natl. Acad. Sci. USA 89, 6497‐6501] gives rise to three phases of membrane potential generation in proteoliposomes with τ values and contributions of ca. 45 μs (20%), 1 ms (20%) and 5 ms (60%). The rapid phase is not sensitive to the binuclear centre ligands, such as cyanide or peroxide, and is assigned to vectorial electron transfer from Cu A to heme a . The two slow phases kinetically match reoxidation of heme a, require added H 2 O 2 or methyl peroxide for full development, and are completely inhibited by cyanide; evidently, they are associated with the reduction of Compound F to the Ox state by heme a . The charge transfer steps associated with the F to Ox conversion are likely to comprise (i) electrogenic uptake of a ‘chemical’ proton from the N phase required for protonation of the reduced oxygen atom and (ii) electrogenic H + pumping across the membrane linked to the F to Ox transition. Assuming heme a ‘electrical location’ in the middle of the dielectric barrier, the ratio of the rapid to slow electrogenic phase amplitudes indicates that the F to Ox transition is linked to transmembrane translocation of 1.5 charges (protons) in addition to an electrogenic uptake of one ‘chemical’ proton required to form Fe 3+ ‐OH − from Fe 4+ = O 2− . The shortfall in the number of pumped protons and the biphasic kinetics of the millisecond part of the electric response matching biphasic reoxidation of heme a may indicate the presence of 2 forms of Compound F, reduction of only one of which being linked to full proton pumping.