On the Absorption of Copper into Yeast Cell

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Abstract
The Cu binding properties were influenced by growth phase of cells, pH and concentration of Cu in reaction mixtures. The efficiency of Cu absorption increased with growth time and was largest at the mid-logarithmic growth phase. The time course of Cu absorption was biphasic, that Cu rapidly bound to cell surface for initial few minutes after addition of Cu and then the Cu was slowly transported into cells. The Cu binding to the cell surface depended on the molecular form of Cu complex in the reaction mixture and the ligand residue to Cu on the cell surface. Double reciprocal plots of absorption velocity of Cu vs. Cu concentration gave straight lines at low concentration between 0.01-0.1 mM. The apparent affinity of Cu to the cells of stationary growth phase was the same as that of logarithmic growth phase, that is, the Km values were about 0.01 mM. At high concentration of Cu between 0.1-5.0 mM the apparent affinity decreased but the absorption velocity of Cu remarkably increased. Zinc sulfate most strongly inhhibited the Cu absorption in this test. Zn competitively bound to the Cu binding sites of cell surface.