Role of mitochondrial NADH kinase and NADPH supply in the respiratory chain activity of <italic>Saccharomyces cerevisiae</italic>

Abstract

<title>Abstract</title> In <italic>Saccharomyces cerevisiae</italic>, the mitochondrial nicotinamide adenine dinucleotide hydride kinase Pos5p is required for a variety of essential cellular pathways, most importantly respiration. The Pos5p knockout strain <italic>pos5</italic>Δ grows poorly in non-fermentable media. A potential relationship between this respiratory deficiency and the ability of the cells to supply nicotinamide adenine dinucleotide phosphate (NADPH) was examined by analyzing the respiratory chain activity of <italic>pos5</italic>Δ and two NADP⁺-specific dehydrogenase mutants, <italic>idp1</italic>Δ and <italic>zwf1</italic>Δ. All of the respiratory chain complexes of <italic>pos5</italic>Δ exhibited poor relative activity of &lt;26% at the middle-log phase and 62% at the stationary phase. The respiratory chain activity levels of <italic>idp1</italic>Δ and <italic>zwf1</italic>Δ also reduced to 22%–37% and 28%–84% at the middle-log phase, and 73%–81% and 67%–88% at the stationary phase, not as robustly as those of <italic>pos5</italic>Δ. The double-mutant <italic>idp1pos5</italic>Δ exhibited even lower activities of &lt;20% at the middle-log phase, but <italic>zwf1pos5</italic>Δ showed similar activities with <italic>pos5</italic>Δ. The complemented strain <italic>POS5</italic>/<italic>pos5</italic>Δ exhibited 1.05- to 3-fold higher activities than <italic>pos5</italic>Δ. These data showed that Pos5p contributes to the maintenance of respiratory chain complex activities, with other NADPH sources, such as Idp1p and Zwf1p, making a smaller contribution. These contributions were partly related to the ability of the cells to supply NADPH, especially in the mitochondria.