Abstract
The sequences of two phosphopeptides isolated from the catalytic subunit of bovine cardiac muscle cAMP-dependent protein kinase (type II) and from two of its cyanogen bromide fragments, have been determined. One phosphorylation site is a threonyl residue located approximately 180 residues from the blocked NH2 terminus. Its sequence is: -Gly-Arg-Thr-Trp-Thr(P)-Leu-Cys- and includes one of the three sulfhydryl groups present in the molecule. The second phosphorylated site within the sequence: -Val-Ser(P)-Ile-Asn- is located towards the carboxyl end of the protein where the other 2 cysteinyl residues also reside. The finding that phosphorylation of the catalytic subunit occurs on two discrete sites rather than at random suggests that it might be of physiological importance, e.g. in the regulation of enzyme activity.
Highlights
From the Howard Hughes Medical Institute and the Department of Biochemistry, University of Washington, Seattle, Washington 98195
Chemical analyses of pure cyanogen bromide fragments obtained from carboxymethylated C subunit indicated the presence of stoichiometric amounts of bound phosphate in three of these only, namely, CB-B, CB-C, and CB-A
The isolation of two phosphopeptides present in two separate CNBr fragments of the C subunit of type II CAMPdependent protein kinase (CB-C and CB-B), one containing threonyl-P and the other seryl-P, is a strong indication that the bound phosphate is an integral part of the structure of the catalytic subunit of CAMP-dependent protein kinase
Summary
From the Howard Hughes Medical Institute and the Department of Biochemistry, University of Washington, Seattle, Washington 98195. Dependent protein kinase (type II) and from two of its cyanogen bromide fragments, have been determined. Cys- and includes one of the three sulfhydryl groups present in the molecule. The second phosphorylated site within the sequence: -Val-Ser(P)-Ile-Asnis located towards the carboxyl end of the protein where the other 2 cysteinyl residues reside. The finding that phosphorylation of the catalytic subunit occurs on two discrete sites rather than at random suggests that it might be of physiological importance, e.g. in the regulation of enzyme activity. Cardiac muscle CAMP-dependent protein kinase can undergo self-phosphorylation on the R subunit and this reaction reduces the rate of reassociation of the isolated subunits in the absence of CAMP [3,5]. Foundation (BMS 7516260), the Muscular Dystrophy Association, Centre National de la Recherche Scientifique (ATP Structure des Proteines), INSERM (CRL 78.4.086.1 and ATP 63-78-75 Biologie et Pharmacologic de la fibre Musculaire Cardiaque), DGRST
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