Compartimentalization of spectrin-phosphorylating enzyme in human erythrocytes

Abstract

Functional characteristics of purified casein kinases from cytosol and membrane of normal human red cell were determined in vitro using pure spectrin as substrate. Both enzyme which differed from each other by their salt solubility, molecular weight and affinity for casein had similar affinity for spectrin and same optimum pH ; they used ATP as phosphoryl donor, were similarly stimulated by monovalent cations and Mg 2+ and inhibited by Ca 2+ and were insensitive to cyclic nucleotides. Cytosol kinase had a poor substrate and phosphoryl donor specificity ; membrane kinase had a much greater affinity for spectrin than for casein and poorly used GTP as phosphoryl donor : it seems to be the physiologically active spectrin kinase of the red cell.