Adenosine 3', 5'-Monophosphate-Dependent Membrane Phosphorylation

Abstract

The role of cyclic adenosine 3', 5'-monophosphate (AMP) in the control of microsomal calcium ion (Ca 2+ ) transport was studied in microsomes prepared from rabbit heart. These cardiac microsomes contained intrinsic cyclic AMP-dependent protein kinase activity that phosphorylated serine residues in a microsomal protein component with a molecular weight of about 20,000 (determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Intrinsic phosphoprotein phosphatase activity of the microsomal membranes resulted in rapid dephosphorylation of these residues. Microsomes phosphorylated in the presence of 1 x 10 -6 M cyclic AMP exhibited enhanced Ca 2+ uptake. We conclude that reversible phosphorylation of microsomal membranes may be an important mechanism for regulation of microsomal Ca 2+ transport by cyclic AMP.