Kinetic studies on cytosol and membrane-bound protein kinases of human erythrocytes

Abstract

1. 1. The cytosol protein kinases of human erythrocytes are resolved by Sepharose 6B filtration into two fractions, the more retarded of which exhibits kinetic and catalytic properties similar to those of protein kinases solubilized from membranes by 0.7 M NaCI. 2. 2. In particular they are able to phosphorylate with the same K m the membrane proteins on their serine and threonine residues, while they phosphorylate almost only serine residues of exogenous proteins such as casein and histones. 3. 3. On the contrary, the larger cytosol protein kinases appear to phosphorylate the membrane proteins to negligible (if any) extent.