The effect of bivalent cations on phosphate uptake by Saccharomyces cerevisiae was investigated. Phosphate uptake via the Na+-dependent transport system at pH 7.2 is stimulated by bivalent cations. The apparent affinity of phosphate for the transport mechanism is increased, but the apparent affinity for Na+ is decreased. Uptake of phosphate via the Na+-independent transport system is accompanied by a net proton influx of 2H+ and an efflux of 1 K+ for each phosphate ion taken up. At pH 4.5 phosphate uptake via the Na+-independent system is stimulated by bivalent cations, whereas at pH 7.2 uptake is inhibited. The effect of bivalent cations on phosphate uptake can be ascribed to a decrease in the surface potential.

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