Key result
Calmodulin-dependent phosphorylation reduces calcium transport ATPase apparent KCa by ~39%.
Calmodulin-dependent phosphorylation increases the calcium sensitivity of the cardiac sarcoplasmic reticulum calcium transport ATPase without changing its maximum capacity.
May sensitize cardiac SR Ca-ATPase to calcium; leaves open relevance to myocardial function in vivo.
The calcium-dependent acylphosphate formed by the calcium transport ATPase of cardiac sarcoplasmic reticulum and the calcium-, calmodulin-dependent phosphoester(s) of sarcoplasmic reticulum fractions formed by a calcium-, calmodulin-dependent membrane-bound protein kinase can be distinguished by removal of calcium and/or magnesium by EDTA or hydroxylamine treatment of the acid denaturated membranes. Both procedures decompose the acylphosphate with little effect on the phosphoester(s). Calmodulin-dependent phosphorylation (2.44 nmol/mg SR protein) reduces the apparent K(Ca) of the acylphosphate steady state level of the calcium transport ATPase from 0.56 to 0.34 microM free calcium, without affecting the maximum phosphoenzyme level (0.93 versus 0.89 nmol/mg protein), and has little, if any, effect on the Hill-coefficient (1.32 versus 1.54).
No takes yet. Share an insight, caveat, or question.
Pifl et al. (1984) studied this question. Calmodulin-dependent phosphorylation vs. Unphosphorylated state was evaluated on Apparent K(Ca) of the acylphosphate steady state level of the calcium transport ATPase. Calmodulin-dependent phosphorylation reduced the apparent K(Ca) of the acylphosphate steady state level of the calcium transport ATPase from 0.56 to 0.34 microM free calcium.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: