Evidence for an endogenous protein inhibitor of sarcoplasmic reticulum calcium pump in heart muscle |
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Authors: | N Narayanan P Lee M Newland R L Khandelwal |
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Affiliation: | 1. Department of Physiology, College of Medicine University of Saskatchewan, Saskatoon, Canada S7N OWO;7. Department of Biochemistry, College of Medicine University of Saskatchewan, Saskatoon, Canada S7N OWO |
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Abstract: | A cytosolic protein fraction, termed CPF-I, derived by (NH4)2 SO4 fractionation of rabbit heart cytosol caused marked inhibition (up to 95%) of ATP-dependent Ca2+ uptake by cardiac sarcoplasmic reticulum. The inhibitory effect of CPF-I was concentration-dependent (50% inhibition with ~ 80–100 μg CPF-I) and heat labile. The inhibitor reduced the velocity of Ca2+ uptake without altering the apparent affinity of the transport system for Ca2+. Concomitant with the inhibition of Ca2+ uptake, Ca2+-sensitive ATP hydrolysis was also inhibited by CPF-I. The inhibitor did not cause release of Ca2+ from Ca2+-preloaded membrane vesicles. The inhibitor activity of CPF-I could be adsorbed to a DEAE cellulose column and could be eluted with a linear gradient of KCl. These results demonstrate the presence of a soluble protein inhibitor of sarcoplasmic reticulum calcium pump in cardiac muscle and raises the intriguing possibility of its participation in the regulation of calcium pump . |
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Keywords: | SR sarcoplasmic reticulum EGTA ethylene glycol bis (β-aminoethyl ether)-N,N′-tetraacetic acid |
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