Distribution of 64Cu in Saccharomyces cerevisiae: kinetic analyses of partitioning

Abstract

The cell association of copper in the yeast Saccharomyces cerevisiae can involve both binding to the cell wall and the accumulation of copper within the cell. The former process requires the concurrent generation of H2S by the cell via the reduction of sulphate. The contributions of each of these processes to the uptake of V u by wild type and met3-containing (ATP sulphurylase-deficient) strains have been kinetically dissected. The Michaelis constant for uptake ( 4 p~) is independent of the type of cell association which is occurring, suggesting, although not requiring, that both processes are associated with a common kinetic intermediate. The time dependence of the cellassociation of 64Cu also suggests the presence of this intermediate pool of bound copper. The Vmax for uptake includes a constant contribution from accumulation of 64Cu within the plasmalemma [ O e l nmol min-' (mg protein)-'] plus that fraction of the 64Cu within the intermediate pool which diffuses away and is trapped on the cell wall as a metal sulphide. This latter contribution to V,,, can be two-to three-times greater than the intracellular uptake depending on the amount and type of sulphur supplementation provided in the 64Cu2+ uptake buffer. Both processes are energy-dependent although the sulphide-dependent periplasmic accumulation is somewhat more sensitive to metabolic inhibition. This can be attributed to the ATP required for the activation of sulphate prior to its reduction to the level of sulphite and then sulphide. Periplasmic 64Cu accumulation is strongly inhibited by Zn2+ and Ni2+. This inhibition is due to competition for cell-generated sulphide; in the presence of %n2+ , the decrease in 64Cu bound is quantitatively related to the amount of 65Zn which becomes cell-associated. In contrast, intracellular 64Cu uptake is not inhibited by these two metals (at 50 p~) showing that the copper translocation pathway is metalspecific. These observations suggest a model for the way newly arrived copper is handled at the cell membrane and is partitioned for intracellular uptake.

Distribution of 64Cu in Saccharomyces cerevisiae: cellular locale and metabolism

“…Quantification of the concentration and time dependencies of the partitioning event(s) which leads to the 64Cu distribution described herein are reported in the following paper (Lin et al, 1993). These kinetic analyses suggest a model for copper uptake and distribution in this yeast.…”

Identification of SLF1 as a New Copper Homeostasis Gene Involved in Copper Sulfide Mineralization in Saccharomyces cerevisiae

“…The pool that is exchangeable with exogenous Cu(II) is believed to be the CuS complexes on the cell surface; the unexchangeable pool is believed to be the cytoplasmic copper pool (26). The exchangeable pool accounts for more than 70% of the Cu associated with yeast cells (26). Although the phenomenon of copper sulfide precipitation around the yeast cell surface has been observed for many years, the functional significance of this pathway was not understood until now.…”

“…In a systematic study on the fate of newly arrived radioactive 64 Cu in wild-type yeast cells, it was found that the cell association of 64 Cu could be divided into two distinguishable pools (26). The pool that is exchangeable with exogenous Cu(II) is believed to be the CuS complexes on the cell surface; the unexchangeable pool is believed to be the cytoplasmic copper pool (26).…”

“…The pool that is exchangeable with exogenous Cu(II) is believed to be the CuS complexes on the cell surface; the unexchangeable pool is believed to be the cytoplasmic copper pool (26). The exchangeable pool accounts for more than 70% of the Cu associated with yeast cells (26).…”

Metal bioaccumulation by Pseudomonas: a way to bioremediation

“…The competition between Cu and Zn for its binding and accumulation on the cell wall has been extensively studied in yeasts [15][16][17]. These authors have reported that Cu uptake in the cell is specific for this metal and is inhibited differentially by Zn.…”