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Two mechanisms for oxidation of cytosolic NADPH by Kluyveromyces lactis mitochondria
Author(s) -
Overkamp Karin M.,
Bakker Barbara M.,
Steensma H. Y.,
van Dijken Johannes P.,
Pronk Jack T.
Publication year - 2002
Publication title -
yeast
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.923
H-Index - 102
eISSN - 1097-0061
pISSN - 0749-503X
DOI - 10.1002/yea.878
Subject(s) - kluyveromyces lactis , biology , biochemistry , mitochondrion , alcohol dehydrogenase , cytosol , pentose phosphate pathway , saccharomyces cerevisiae , dehydrogenase , glycolysis , enzyme , yeast
Abstract Null mutations in the structural gene encoding phosphoglucose isomerase completely abolish activity of this glycolytic enzyme in Kluyveromyces lactis and Saccharomyces cerevisiae . In S. cerevisiae , the pgi1 null mutation abolishes growth on glucose, whereas K.lactis rag2 null mutants still grow on glucose. It has been proposed that, in the latter case, growth on glucose is made possible by an ability of K. lactis mitochondria to oxidize cytosolic NADPH. This would allow for a re‐routing of glucose dissimilation via the pentose‐phosphate pathway. Consistent with this hypothesis, mitochondria of S. cerevisiae cannot oxidize NADPH. In the present study, the ability of K. lactis mitochondria tooxidize cytosolic NADPH was experimentally investigated. Respiration‐competent mitochondria were isolated from aerobic, glucose‐limited chemostat cultures of the wild‐type K. lactis strain CBS 2359 and from an isogenic rag2Δ strain. Oxygen‐uptake experiments confirmed the presence of a mitochondrial NADPH dehydrogenase in K.lactis . This activity was ca. 2.5‐fold higher in the rag2Δ mutant than in the wild‐type strain. In contrast to mitochondria from wild‐type K. lactis , mitochondria from the rag2Δ mutant exhibited high rates of ethanol‐dependent oxygen uptake. Subcellular fractionation studies demonstrated that, in the rag2Δ mutant, a mitochondrial alcohol dehydrogenase was present and that activity of a cytosolic NADPH‐dependent ‘acetaldehyde reductase’ was also increased. These observations indicate that two mechanisms may participate inmitochondrial oxidation of cytosolic NADPH by K. lactis mitochondria: (a) direct oxidation of cytosolic NADPH by a mitochondrial NADPH dehydrogenase; and (b) a two‐compartment transhydrogenase cycle involving NADP + ‐ and NAD + ‐dependent alcohol dehydrogenases. Copyright © 2002 John Wiley & Sons, Ltd.