The polypeptides of the human erythrocyte membrane were analyzed by polyacrylamide gel electrophoresis in 1 % sodium dodecyl sulfate. Six major bands (I-VI) together make up over two-thirds of the protein staining profile. Component III (mol wt 89,000) predominates in the ghost membrane; it constitutes 30% of the protein and numbers over 106 chains/ghost. Components I and II form a slow-moving doublet (approximate mol wt 250,000) containing 25 % of the protein. The molar amounts of I + II, IV (mol wt 77,500),

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ERYTHROCYTE MEMBRANE PROTEIN KINASES. Isuits have to be compared with the properties of pure lipidprotein complexes.major 215,000-dalton polypeptide-has several distin-. guishing features. The reaction is manifested at Mg2+ concentrations above 10-4 M and is relatively unresponsive to 20 /itM cyclic AMP. It is stimulated by Ca2+ at 1 mM and by Na+, K+, Li+, and NFLt+ at 0.05 and 0.2 M. No turnover of this peptide-bound 32P can be detected in the isolated membrane. The 215,000-dalton polypeptide is the only substrate utilized in this reaction. All other endogenous phosphorylations, particularly those strongly stimulated by cyclic AMP, are inhibited by Ca2+ and/or by monovalent E/rythrocyte membranes require ATP in the performance of a variety of functions. In the active transport of cations, ATP serves directly as a substrate and there is a fixed stoichiometry between ATP hydrolysis and the number of cations translocated. This type of function is well reflected in a