Iron Reduction and Trans Plasma Membrane Electron Transfer in the Yeast Saccharomyces cerevisiae.
The ferri-reductase activity of whole cells of Saccharomyces cerevisiae (washed free from the growth medium) was markedly increased 3 to 6 h after transferring the cells from a complete growth medium (preculture) to an iron-deficient growth medium (culture). This increase was prevented by the presence of iron, copper, excess oxygen, or other oxidative agents in the culture medium. The cells with increased ferri-reductase activity had a higher reduced glutathione content and a higher capacity to expose exofacial sulfhydryl groups. Plasma membranes purified from those cells exhibited a higher reduced nicotinamide adenine phosphate (NADPH)-dependent ferri-reductase specific activity. However, the intracellular levels of NADPH, NADH, and certain organic acids of the tricarboxylic acids cycle were unchanged, and the activity of NADPH-generating enzymes was not increased. Addition of Fe(III)-EDTA to iron-deprived and iron-rich cells in resting suspension resulted in a decrease in intracellular reduced glutathione in the case of iron-deprived cells and in an increase in organic acids and a sudden oxidation of NADH in both types of cells. The depolarizing effect of Fe(3+) was more pronounced in iron-rich cells. The metabolic pathways that may be involved in regulating the trans-plasma membrane electron transfer in yeast are discussed.
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Laboratoire de Biochimie des Porphyrines, Institut J. Monod, Tour 43, Université Paris 7, 2 Place Jussieu, 75251 Paris Cedex 05, France.
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