Regulation of the plant alternative oxidase by pyruvate

Crichton, Paul G, Affourtit, Charles, Albury, Mary S, Carré, Jane E and Moore, Anthony L (2004) Regulation of the plant alternative oxidase by pyruvate. p. 164. ISSN 0005-2728

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In addition to a conventional cytochrome pathway, plant mitochondria contain a second, nonprotonmotive route of electron
transfer, comprised of a single ubiquinol:oxygen oxidoreductase, the alternative oxidase (AOX). This enzyme is regulated by
two interrelated posttranslational mechanisms. Firstly, reduction of an intermolecular disulphide bond results in an ‘activated’
noncovalently linked dimer. Secondly, the reduced protein is further stimulated by a-keto acids, most notably pyruvate. This is
thought to occur via a-keto acid interaction with a well-conserved cysteine residue. Previously, we have established a system to
functionally express the Sauromatum guttatum alternative oxidase (Sg-AOX) in the fission yeast Schizosaccharomyces pombe.
Interestingly, the resulting antimycin-resistant respiratory activity in isolated yeast mitochondria, does not appear to be
stimulated by pyruvate.
Here, we report on the expression of both Sg-AOX as well as a second plant isozyme, the Arabidopsis thaliana AOX1a
protein (At-AOX1a), in the same yeast system. In contrast to Sg-AOX, At-AOX1a-dependent activity can be stimulated by
pyruvate f1.4-fold in isolated yeast mitochondria and f4.5-fold in isolated mitochondrial membranes depleted of
endogenous pyruvate. Whilst Sg AOX activity is confirmed to be completely independent of pyruvate, its dependence upon
the Q-redox poise would suggest that it is in a constitutively active state, comparable to the ‘pyruvate-activated’ kinetic
dependence of At AOX1a. These data indicate that Sg AOX is the first example of a plant enzyme that appears to function
without a dependence on organic acids for full activity. This finding is of particular interest, given that both Sg AOX and At
AOX1a conserve the cysteine residue believed to interact directly with pyruvate. As both proteins exhibit a very similar
primary structure, we have been able to identify structural components, additional to the regulatory cysteine, that may account
for the differences in the regulatory behaviour reported here. The implications of such findings are discussed in terms of the
proposed structure of AOX.

Item Type: Article
Additional Information: Conference Information: 13th European Bioenergetics Conference (EBEC 2004)
Schools and Departments: School of Life Sciences > Biochemistry
Depositing User: Mary Albury
Date Deposited: 06 Feb 2012 21:03
Last Modified: 31 May 2013 12:31
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