Some characteristics of Ca²⁺ uptake by yeast cells

Summary

Experiments were performed to obtain information on: (i) the specific properties of Ca²⁺ binding and transport in yeast (ii) the relationship between both parameters; (iii) similarities to or differences from other biological systems as measured by the effects of inhibitors; and (iv) the effects of mono and divalent cations, in order to get some insight on the specificity and some characteristics of the mechanism of the transport system for divalent cations in yeast.

The results obtained gave some kinetic parameters for a high affinity system involved in the transport of Ca²⁺ in yeast. These were obtained mainly by considering actual concentrations of Ca²⁺ in the medium after substracting the amounts bound to the cell. Ak _m of 1.9 μm and aV _max of 1.2 nmol (100 mg·3 min)⁻¹ were calculated.

The effects of some inhibitors and other cations on Ca²⁺ uptake allow one to postulate some independence between binding and transport for this divalent cation.

Of the inhibitors tested, only lanthanum seems to be a potent inhibitor of Ca²⁺ uptake in yeast.

The effects of Mg²⁺ on the uptake of Ca²⁺ agree with the existence of a single transport system for both divalent cations.

The actions of Na⁺ and K⁺ on the transport of Ca²⁺ offer interesting possibilities to study further some of the mechanistic properties of this transport system for divalent cations.