Functional significance of quaternary organization of the sarcoplasmic reticulum Ca2+-ATPase

There is both structural and functional evidence for protein-protein interaction between Ca2+-ATPase polypeptide chains in the sarcoplasmic reticulum membrane. Studies on detergent solubilized ATPase indicate that the monomeric form is capable of performing a normal cycle of ATP hydrolysis, but some of the modulatory effects of the substrates disappear after detergent solubilization. However, the necessity of protein-protein interactions for the Ca2+ transport function remains unclarified. A new approach is described, employing ATPase reconstituted with a large excess of phospholipid, which may help to resolve this question.