ISSN:
1432-072X
Keywords:
Paracoccus denitrificans
;
Cytochrome o
;
Myxothiazol
;
Ubiquinone
;
Electron transport chain branching
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The organisation and function of electron transport pathways in Paracoccus denitrificans has been studied with both inhibitors and electrode probes for O2 or N2O respiration and membrane potential. Myxothiazol completely inhibits electron flow through the cytochrome bc1 region of the electron transport chain, as judged by its effect on nitrous oxide respiration. Electron flow to oxygen via the cytochrome o oxidase was shown to be insensitive to myxothiazol in a mutant, HUUG 25, that lacks cytochrome c and in which the aa3 oxidase is therefore inactive. Myxothiazol did not inhibit nitrate reduction. It is concluded that myxothiazol is a specific inhibitor of electron flow through the cytochrome bc1 region and more potent than antimycin which does not give complete inhibition. As neither antimycin nor myxothiazol, nor a combination of the two, inhibits electron transport to either nitrate reductase or cytochrome o it is concluded that electron transport pathways to these enzymes do not involve the cytochrome bc1 region but rather branch at the level of ubiquinone. Although the cytochrome o pathway branches at ubiquinone, it is associated with the generation of a protonmotive force; this is shown by measurements of membrane potential in vesicle preparations from the mutant HUUG 25. In contrast to antimycin and myxothiazol, the ubiquinone analogues 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole (UHDBT) and 2-n-undecyl-3-hydroxy-1,4-naphthoquinone (UHNQ) inhibit electron flow through both the cytochrome bc1 complex and the cytochrome o pathway, although a higher titre is required in the latter case. These two inhibitors were without effect on the nitrate reductase pathway. Thus myxothiazol is the inhibitor of choice for selective and complete inhibition of cytochrome bc1. Recently published schemes for electron transport in P. denitrificans are analysed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00446779
Permalink