JBC, Vol. 250, Issue 23, 9044-9052, Dec, 1975
Adenosine 3':5'-monophosphate-regulated phosphorylation of erythrocyte membrane proteins. Separation of membrane-associated cyclic adenosine 3':5'-monophosphate-dependent protein kinase from its endogenous substrates
C. S. Rubin
An adenosine 3':5'-monophosphate (cyclic AMP)-binding protein in the human
erythrocyte plasma membrane was isotopically labeled using a photoaffinity
analog of cyclic AMP, N6-(ethyl 2-diazomalonyl) cyclic [3H]AMP. The cyclic
AMP-binding site is located in a polypeptide chain having a molecular
weight of 48,000. Cyclic AMP-binding protein and cyclic AMP-dependent
protein kinase were solubilized with 0.5% Triton X-100 in 56 mM sodium
borate, pH 8, but 32P-labeled membrane phosphoproteins were retained in the
Triton-insoluble fraction, suggesting that the membrane-associated binding
protein is not a primary substrate for protein kinase. Triton-solubilized
and membrane-associated protein kinase activities were stimulated 15- and
17-fold by cyclic AMP, suggesting that the degree of association between
the catalytic anc cyclic AMP-binding components was very similar in both
preparations. Fractionation and characterization of membrane
phosphoproteins have shown that protein III and a co-migrating minor
protein are substrates for protein kinase but membrane sialoglycoproteins
are not phosphorylated.