Role of sarcoplasmic reticulum phospholipids in calcium ion binding activity

Abstract

The relationship between sarcoplasmic reticulum phospholipid and Ca2+ binding by sarcoplasmic reticulum membraneswas explored. Ca2+ bound in the absence of ATP was defined as “ATP-independent Ca2+ binding,” and the additional amount of Ca2+ bound in the presence of ATP was defined as “ATP-dependent Ca2+ binding.” The latter was found to be very sensitive to the loss of sarcoplasmic reticulum phospholipid; the amount of Ca2+ bound was reduced when as little as 3% of the phospholipid was destroyed by phospholipase C. Further destruction of membrane phospholipid up to a 40% loss caused little or no further reduction of this Ca2+ binding. However, when the destruction of phospholipid exceeded 40%, further loss of this Ca2+ binding occurred, andthere was an almost complete loss of this function when more than 60% of the sarcoplasmic reticulum phospholipid was destroyed.

Keywords

• phospholipase C
• “ATP-dependent Ca2+ binding”
• “ATP-independent Ca2+ binding”
• “ATP-dependent, oxalate-promoted Ca2+ transport”