The mycotoxin, cyclopiazonic acid (CPA), inhibits the Ca2+-stimulated ATPase (EC 188.8.131.52) and Ca2+ transport activity of sarcoplasmic reticulum (Goeger, D.E., Riley, R.T., Dorner, J.W., and Cole, R.J. (1988) Biochem. Pharmacol. 37, 978-981). We found that at low ATP concentrations (0.5-2 μM) the inhibition of ATPase activity was essentially complete at a CPA concentration of 6-8 nmol/mg protein, indicating stoichiometric reaction of CPA with the Ca2+-ATPase. Cyclopiazonic acid caused similar inhibition of the Ca2+-stimulated ATP hydrolysis in intact sarcoplasmic reticulum and in a purified preparation of Ca2+-ATPase. Cyclopiazonic acid also inhibited the Ca2+-dependent acetylphosphate, p-nitrophenylphosphate and carbamylphosphate hydrolysis by sarcoplasmic reticulum. ATP protected the enzyme in a competitive manner against inhibition by CPA, while a 105-fold change in free Ca2+ concentration had only moderate effect on the extent of inhibition. CPA did not influence the crystallization of Ca2+-ATPase by vanadate or the reaction of fluorescein-5'-isothiocyanate with the Ca2+-ATPase, but it completely blocked at concentrations as low as 1-2 mol of CPA/mol of ATPase the fluorescence changes induced by Ca2+ and [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA) in FITC-labeled sarcoplasmic reticulum and inhibited the cleavage of Ca2+-ATPase by trypsin at the T2 cleavage site in the presence of EGTA. These observations suggest that CPA interferes with the ATP-induced conformational changes related to Ca2+ transport. The effect of CPA on the sarcoplasmic reticulum Ca2+-ATPase appears to be fairly specific, since the kidney and brain Na+, K+-ATPase (EC 184.108.40.206), the gastric H+,K+-ATPase (EC 220.127.116.11), the mitochondrial F1-ATPase (EC 18.104.22.168), the Ca2+-ATPase of erythrocytes, and the Mg2+-activated ATPase of T-tubules and surface membranes of rat skeletal muscle were not inhibited by CPA, even at concentrations as high as 1000 nmol/mg protein.
|Number of pages||8|
|Journal||Journal of Biological Chemistry|
|Publication status||Published - Jan 1 1989|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology