The Influence of Calcium Ions on the Preparation of the (Ca²⁺ + Mg²⁺)-Activated Membrane ATPase in Human Red Cells

Abstract

Membranes were prepared from red cells both in the presence of 0.4–0.5 mmol/l Ca²⁺ and without Ca²⁺. The Ca²⁺-stimulated ATPase of membranes prepared without Ca²⁺ showed reduced specific activity, decreased affinity towards Ca²⁺, and a pH optimum of 7.40 compared to a pH optimum of 7.15 of the Ca²⁺-stimulated ATPase of Ca²⁺-treated membranes. The phenomena are possibly due to the formation of a modified state of the ATPase in the membranes prepared without Ca²⁺.

Key Words:

• ATPase
• calcium
• erythrocyte
• freezing
• haemolysis
• human
• membrane
• pH
• preparation