[Inhibition of the activity of membrane-bound Ca2+-ATPase in the sarcoplasmic reticulum fragments of rabbit skeletal muscles by the alkaloid sanguinarine].

Sanguinarine, a plant DNA-intercalator, is shown to inhibit the enzyme activity of the membrane-bound Ca2+-ATPase of rabbit skeletal muscle sarcoplasmic reticulum fragments. This inhibition could be interpreted by the well known ability of this alkaloid to interact with sulphydryl groups of the enzymes. Sanguinarine is a weaker inhibitor of this reaction than a sulphydryl group poison Ag+. The I50 is 3.10(-6) M for Ag+ and 7.10(-5) M for sanguinarine in the reaction medium with NO3- substituted for Cl-. In the standard reaction medium containing Cl-, the I50 for sanguinarine is 1.8.10(-4) M. In this case sanguinarine activates Ca2+-ATPase at low concentrations presumably because of uncoupling ATP hydrolysis from Ca2+ transport through membrane. Other agents studied are: DNA-intercalators--ethidium bromide, acriflavine, acridine orange; DNA-complexing antibiotics--actinomycin D, and olivomycin, alkaloids, quinine, morphine, berberine and an uncoupler of oxidative phosphorylation 2,4-dinitrophenol. These were found not to inhibit Ca2+-ATPase activity up to the concentrations of 10(-3)-10(-4) M.