JBC, Vol. 250, Issue 16, 6355-6361, Aug, 1975
Effect of denaturation on the susceptibility of proteins to enzymic phosphorylation
D. B. Bylund and E. G. Krebs
Heat-denatured chicken egg white lysozyme and the reduced carboxymethylated
maleylated derivative of this protein were found to serve as substrates for
rabbit skeletal muscle cyclic AMP-dependent protein kinase. The native form
of the protein was not a substrate. Two phosphoryl groups per mole of
lysozyme were incorporated in the reaction. It was determined that the
phosphoryl moieties were bound to serine 24 and serine 50 in the modified
protein. Serine 24 was phosphorylated approximately 3 times as fast as
serine 50. Reduced carboxymethylated maleylated derivatives of bovine serum
albumin, phosphorylase b, and creatine kinase also served as substrates for
the protein kinase whereas their native forms did not. The reduced
carboxymethylated maleylated derivative of the inhibitory subunit of
troponin was a poorer substrate than the native form of the protein.
Maleylated histones F1 and F2b were also poorer substrates than the
nonderivatized forms. The significance of these experiments with reference
to the specificity of cyclic AMP-dependent protein kinase is discussed.