HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Tang, H. L. Articles by Trumpower, B. L. Search for Related Content PubMed PubMed Citation Articles by Tang, H. L. Articles by Trumpower, B. L. Social Bookmarking                      What's this?

J. Biol. Chem., Vol. 261, Issue 14, 6209-6215, 05, 1986

Triphasic reduction of cytochrome b and the protonmotive Q cycle pathway of electron transfer in the cytochrome bc1 complex of the mitochondrial respiratory chain

HL Tang and BL Trumpower

Reduction of cytochrome b in isolated succinate-cytochrome c reductase is a triphasic reaction. Initially, there is a relatively rapid, partial reduction of the cytochrome b, the rate of which matches the rate of reduction of cytochrome c1. This is followed by partial or complete reoxidation of the b, which is then followed by slow rereduction. At very low concentrations of succinate, the initial partial reduction of b is followed by reoxidation, but the third (rereduction) phase is absent, owing to insufficient substrate to rereduce the cytochromes. If antimycin is added at various times during the triphasic reaction, it inhibits the reoxidation and also inhibits the rereduction phase. Antimycin does not inhibit the initial phase of b reduction and, if added before or during this phase, it causes reduction of b to proceed to completion as a monophasic reaction. Myxothiazol inhibits the first phase of b reduction and the subsequent reoxidation, but does not inhibit the third, slow phase of b reduction. The resulting monophasic reduction of b which is observed in the presence of myxothiazol is slower than that in the presence of antimycin. The combination of both inhibitors, whether added together or successively during the triphasic reaction, completely inhibits b reduction. The triphasic reduction of cytochrome b is consistent with electron transfer by a protonmotive Q cycle in which there are two pathways for cytochrome b reduction. One pathway allows the initial phase of cytochrome b reduction by a myxothiazol-sensitive reaction in which reduction of b by ubisemiquinone is linked to reduction of iron- sulfur protein and cytochrome c1 by ubiquinol. In the second phase of the triphasic reaction, the b cytochromes are reoxidized by ubiquinone or ubisemiquinone through an antimycin-sensitive reaction. If oxidation of ubiquinol by iron-sulfur protein is blocked, either by myxothiazol or by reduction of iron-sulfur protein and cytochrome c1, the b cytochromes can be reduced by reversal of the antimycin-sensitive pathway, thus accounting for the third phase of b reduction.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				C. H. Snyder and B. L. Trumpower Ubiquinone at Center N Is Responsible for Triphasic Reduction of Cytochrome b in the Cytochrome bc1 Complex J. Biol. Chem., October 29, 1999; 274(44): 31209 - 31216. [Abstract] [Full Text] [PDF]