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Hyperthyroidism affects the activity of a cAMP-dependent protein kinase and protein phosphorylation in heart
K S Famulski1, G Szymańska, P Szymański
1Nencki Institute of Experimental Biology, Department of Muscle Biochemistry, Warsaw, Poland.
Abstract:
We have investigated the effect of thyroxine administration on the cAMP related systems in heart sarcolemma. Hyperthyroidism produces an increase in the number of beta-receptors and enhances in situ the phosphorylation of some sarcolemmal proteins, in particular the 55 kDa peptide. On the other hand, the activity of a membrane-bound cAMP-dependent protein kinase is considerably lower in sarcolemma obtained from animals receiving the hormone. We suggest that the thyroxine-induced alteration in beta-receptors elevates the content of cAMP in the cell which, in turn, evokes a transient dissociation of the catalytic subunit of a cAMP-dependent kinase from the regulatory subunit embeded in the membrane.