Phospholamban stoichiometry in canine cardiac muscle sarcoplasmic reticulum

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Abstract
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 1∶1, phospholamban:125I-calmodulin complex. In parallel experiments, sarcoplasmic reticulum was phosphorylated in the presence of calmodulin and [γ-32P]ATP, and then treated with the crosslinking reagent to produce an affinity labeled component consisting of a 1∶1, 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.

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