Molecular mechanism by which cyclic amp regulates myocardial contractility Page: 35 of 153
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rate of ATP hydrolysis by the Ca^++Mg^+-ATPase in the
sarcoplasmic reticulum is also increased in the presence of cyclic
AMP (Tada et aK, 1974). However, the amount of phosphorylated
intermediate from the ATPase did not vary with
cyclic AMP (Tadaet^L, 1978, 1979).
To elucidate the molecular mechanism by which cyclic AMP
enhances myocardial contractility, the phosphorylation of cardiac
microsomes by cyclic AMP-dependent protein kinase has been
investigated. A 22,000-dalton protein from cardiac sarcoplasmic
reticulum has been shown to be phosphorylated specifically by
cyclic AMP-dependent protein kinase (Tada et^l_., 1975). This
phosphoprotein has characteristics of phosphoester bonding. The
phosphate group is removed by phosphatases (Tada et jtl_., 1975; Tada
j?t_al_., 1978). In addition, Jones et al. (1979) have recently
described the separation and characterization of the sarcoplasmic
reticulum and the sarcolemmal membranes. They reported that cyclic
AMP-dependent protein kinase stimulates the phosphorylation of a
20.000 and a 7,000 dal ton protein in the sarcoplasmic reticulum and
proteins of molecular weights, 155,000, 90,000, 56,000, 24,000 and-
11.000 in the sarcolenmal membranes. The present communication
confirms and extends the findings of Jones et _al_. (1979) and
Bidlack and Shamoo (1979). In addition to the 22,000 dalton
protein, another protein with a molecular weight of 6,000 is also
specifically phosphorylated by cyclic AMP-dependent protein
kinase. This protein has properties similar to the 22,000 dalton
protein. Extrinsic before phosphorylation, the phosphorylation of
both proteins causes them to become intrinsic, buried in the
membrane.
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Bidlack, J. M. Molecular mechanism by which cyclic amp regulates myocardial contractility, report, January 1, 1979; United States. (https://digital.library.unt.edu/ark:/67531/metadc1085147/m1/35/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.