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A mechanism for the reduction of cytochromes by quinols in solution and its relevance to biological electron transfer reactions
Author(s) -
Rich Peter R.,
Bendall Derek S.
Publication year - 1979
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(79)80608-0
Subject(s) - citation , relevance (law) , chemistry , library science , computer science , philosophy , law , political science
The mechanism by which reducing power is transferred from the biological quinols, ubiqninol and plastoquinol, to their respective acceptors, presumably cytochrome cl in mitochondria and cytochrome f of chloroplasts, is obscure. The difficulty arises from the fact that, at around neutral pH, the quinols are primarily two-equivalent hydrogen atom donors, whereas their acceptors are primarily one-equivalent electron acceptors. This immediately raises the qnestion of the properties and possible fates of the intermediate semiquinone species which are inevitably involved. Furthermore, the feasibility of a significant reaction rate may be questioned when one considers the quinol/semiquinone couple which is operative in the first step of the reaction sequence it has already been noted that such a couple would have an extremely high midpoint potential if the semiqu~one species is highly unstable (see Clark [ 1 ] for a mathematical treatment of this). These problems have become particularly relevant recently with the notion of a central role of quinone in the protonmotive function of site II of the mitochondrial respiratory chain and of the region of the chloroplast chain between the two photosystems [2]. A useful development has been the concept of bound qninone species which have altered properties, in particular such that the ~miqu~one species is stabilised and hence lowering the midpoint potential of the quinol/semiquinone couple [2] so that a reasonable reaction rate is possible. However, whereas support for such a system has been gained for the site of electron donation into the quinone pool in both