Iron Reduction and Trans Plasma Membrane Electron Transfer in the Yeast Saccharomyces cerevisiae

Abstract

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(lll)-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 Fe3" 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.The reductive pathway of iron assimilation in plants and microorganisms involves reduction of ferric iron, either at the cell surface via a trans-plasma membrane redox system, or in the extracellular medium via excreted reducing compounds. Iron is then taken up by the cells as soluble Fe2" ions (1,8,21).We have previously shown that yeast cells, Saccharomyces cerevisiae, exhibit a ferri-reductase activity that is dramatically increased in response to iron limitation. We provided both physiological and genetic evidence that the reductase activity was required for the uptake of iron by the cells from several ferric chelates (15)(16)(17). Heme-deficient mutants, which were shown to be also deficient in ferri-reductase activity, are unable to take up iron efficiently from ferric citrate (16). Our results were recently confirmed by the work of Dancis et al. (6), who also isolated a ferri-reductase-deficient mutant.

Formation of Root Epidermal Transfer Cells in Plantago

“…The proton pump is an indispensable part of the Fe acquisition by strategy I plants, since it enhances the solubility of Fe oxides and generates the proton motive force for the uptake of Fe. Moreover, the activity of the H+-ATPase seems to be necessary for the reduction of ferric Fe in terms of membrane potential homeostasis (Lesuisse and Labbe, 1992;Schmidt, 1993). In roots of Plantago, net proton efflux of Fe-deficient plants was observed neither in hydroponic solution during a period of 10 d nor in agar medium, which is more sensitive because of limited diffusion of the protons excreted (data not shown).…”

Ferrioxamines B and E as iron sources for the marine diatom Phaeodactylum tricornutum

“…The involvement of a reductive mechanism for iron uptake is common among organisms. It has been reported for higher plants (Chaney et al 1972), bacteria (Reissbrodt 1994) and yeast cells (Lesuisse & Labbe 1992). In phytoplankton, the presence of plasmalemma redox enzymes and their importance for iron uptake are well documented (Jones et al 1987).…”

Iron: Nutritious, Noxious, and Not Readily Available

“…This is in contrast to earlier work that suggested, on the basis of inhibitor studies, that Fe(I1) might be transported by the common divalent cation transporter that transports zinc, cobalt, and nickel. The observation that the yeast PM Fe(II1) reductase is not only involved in reductive iron uptake but plays a more general role in modifying the redox potential of cells may also be true for plants (Lesuisse and Labbe, 1992;Welch et al, 1993). A comparison of information available on plants and yeast also reveals some differences.…”

“…A comparison of information available on plants and yeast also reveals some differences. Unlike plants, there does not appear to be any involvement of intracellular citrate or malate in the trans-PM redox system of yeast, nor is there any substantial difference in the transmembrane electrical potentia1 of iron-sufficient and iron-deficient cells of yeast (Lesuisse and Labbe, 1992). The yeast Fe(II1) reductase utilizes NADPH, whereas the plant Fe(II1) reductase preferentially utilizes NADH (Holden et al, 1994).…”