RECONSTITUTION OF RABBIT SARCOPLASMIC-RETICULUM CALCIUM-ATPASE IN A SERIES OF PHOSPHATIDYLCHOLINES CONTAINING A SATURATED AND AN UNSATURATED CHAIN - SUGGESTION OF AN OPTIMAL LIPID ENVIRONMENT

The calcium-dependent ATPase from sarcoplasmic reticulum of rabbit has been purified and reconstituted in dispersions containing pure phosph atidylcholines. Each phosphatidylcholine (PC) had palmitate (16:0) at the sn-1 position of glycerol and stearate (18:0), oleate (18:1), lino leate (18:2), arachidonate (20:4), or docosahexaenoate (22:6) at the s n-2 position. The activities and activation energies of the enzyme ind icated that the best enzyme function occurred when 16:0-18:1 PC or 16: 0-18:2 PC was the lipid in which the ATPase was embedded. Circular dic hroism measurements made as a function of temperature suggested that t he protein in 16:0-18:0 and 16:0-18:1 PC behaved most like sarcoplasmi c reticulum or purified ATPase. The results suggest that there may be an optimal lipid environment for the ATPase which is provided by 16:0- 18:1 PC and 16:0-18:2 PC, the two most common lipids of the sarcoplasm ic reticulum.