Calmodulin stimulation of 45Ca2+ transport and protein phosphorylation in cholinergic synaptic vesicles.
Cholinergic synaptic vesicles isolated from the electric organ of Torpedo californica exhibit ATP-dependent uptake of 45Ca2+ that is stimulated by exogenous calmodulin. ATP-independent uptake also occurs, but it is only weakly stimulated by calmodulin. Saturating calmodulin decreased the Michaelis constant for ATP-dependent 45Ca2+ uptake from 52 +/- 0.4 to 12 +/- 0.2 microM and increased the maximal velocity from 3.4 +/- 0.3 to 5.2 +/- 0.5 nmol/mg of protein per min. The dose-response curve for calmodulin-dependent stimulation showed a maximal increase of 3.5-fold in the uptake rate; 0.2 microM calmodulin gave half-maximal stimulation. The activity of the vesicle-associated ATPase was unaffected. Incubation of vesicles with [gamma-32P]ATP and Ca2+ resulted in phosphorylation of four polypeptides of molecular weights about 64,000, 58,000, 54,000, and 41,000 when calmodulin was added. Vesicles that were previously phosphorylated and purified exhibited 2-fold enhanced ATP-independent uptake of 45Ca2+. Cyclic AMP could not substitute for calmodulin. The calcium transport system of the cholinergic synaptic vesicle is regulated by a calcicalmodulin-dependent protein kinase that is vesicle-associated.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D004557:Electric Organ / Q000378:metabolism*; D007700:Kinetics; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011950:Receptors, Cholinergic / Q000502:physiology; D013572:Synaptic Vesicles / Q000187:drug effects / Q000378:metabolism*; D014101:Torpedo
D002135:Calcium-Binding Proteins; D002147:Calmodulin; D009419:Nerve Tissue Proteins; D011950:Receptors, Cholinergic; D000001:Calcimycin; D011494:Protein Kinases; D002118:Calcium