[Simulation of lipid environment of Ca-dependent ATPase from the sarcoplasmic reticulum of skeletal muscles by non-ionic detergents].

To determine the conditions under which the Ca-ATPase from rabbit skeletal sarcoplasmic reticulum can be restored to full activity, a systematic study of reactivation of lipid-depleted enzyme by various non-ionic detergents and surfactants has been carried out. All the non-ionic detergents used were able to reactivate the enzyme. The reactivation potencies of the detergents are closely related to a relative size of their polar head group and hydrophobic hydrocarbon chains. The so-called HLB (hydrophyle/lipophyle balance) numbers were used to estimate the relative hydrophobicities of the detergents studied. A striking correlation between the reactivation potency and the HLB number of any detergent was observed; the inverse correlation coefficient for small samples if equal to -0.95 +/- 0.09. The proper orientation of the ATPase protein in two different phases (lipophyle and hydrophyle) seems to be restored during reactivation. In many cases the protein-bound detergent simulates the lipid environment in the membrane sufficiently well to support the continued activity of the Ca-ATPase.