Phospholamban stoichiometry in canine cardiac muscle sarcoplasmic reticulum

Treatment of cardiac sarcoplasmic reticulum with the crosslinking reagent dithiobis (succinimidyl propionate) in the presence of¹²⁵I-calmodulin, resulted in the formation of a 40,000-dalton affinity labeled component, consisting of a 11, phospholamban:¹²⁵I-calmodulin complex. In parallel experiments, sarcoplasmic reticulum was phosphorylated in the presence of calmodulin and [-³²P]ATP, and then treated with the crosslinking reagent to produce an affinity labeled component consisting of a 11, calmodulin:³²P-phospholamban complex. These experiments permitted determination of the amount of¹²⁵I and³²P incorporated into the 40,000-dalton complexes, as well as the amount of³²P incorporated into the 23,000-dalton form of phospholamban. If 1 mol of Ca²⁺-dependent ATPase phosphoprotein represents 1 mol of 100,000-dalton Ca²⁺-dependent ATPase monomer, then there are 4.88±1.33 mol Ca²⁺-dependent ATPase/mol of phospholamba. If there are 2 mol of Ca²⁺-dependent ATPase phosphoprotein/mol of 100,000-dalton Ca²⁺-dependent ATPase monomer, then there are 9.76±2.66 mol Ca²⁺-dependent ATPase/mol phospholamban.Special issue dedicated to Dr. E. M. Shooter and Dr. S. Varon.