Effects of canatoxin on the Ca(2+)-ATPase of sarcoplasmic reticulum membranes.

Canatoxin, a toxic protein isolated from the seeds of Canavalia ensiformis, was studied for its effects on the sarcoplasmic reticulum vesicles obtained from rabbit skeletal muscle. Canatoxin inhibited Ca2+ accumulation catalysed by the Ca(2+)-ATPase, without affecting the hydrolytic activity of this enzyme or membrane permeability to Ca2+. The effects of canatoxin were dose dependent, but not time dependent. It is concluded that canatoxin interacts with the Ca2+ pump and uncouples Ca2+ uptake from Ca(2+)-dependent ATP hydrolysis.