Temperature effects on kinetic properties of plasma membrane ATPase from the yeast Saccharomyces cerevisiae.

The reaction of plasma membrane ATPase from yeast with Mg2+ and Mg X ATP was studied in a temperature range of 10-30 degrees C. The random mechanism of activation by Mg2+ and the pseudocompetitive inhibition at higher concentrations was not altered when the temperature was varied, nor were the kinetic constants representing substrate binding. However, at low temperature, the affinity of the enzyme for Mg2+ is greatly reduced. The Arrhenius plot of log V vs. 1/T shows straight lines with an inflection point at 24 degrees C, which disappears in the presence of detergent. Calorimetric studies of the plasma membranes show a transition point at the same temperature. From these findings we suppose that Mg2+ is bound at a regulatory site of the ATPase, which is influenced by surrounding phospholipids.