The effect of membrane potential on the limited tryptic digestion of the sarcoplasmic reticulum Ca(2+)-ATPase.

The tryptic cleavage process of the sarcoplasmic reticulum Ca(2+)-ATPase was analysed under the influence of experimentally generated membrane potential. The digestion of the Ca2+ transport enzyme was stopped before the dissipation of the potential response. The cleavage products reflected the actual conformation of the enzyme as the low Ca2+ affinity E2, under the influence of inside positive, and as the high Ca2+ affinity E1 conformation under the influence of inside negative potential. These results provide further support for the possible role of transient membrane potential changes in the regulation of the conformational equilibrium of the sarcoplasmic reticulum Ca2+ pump enzyme.