Abstract
Procedures are described by which troponin and tropomyosin can be isolated from cardiac muscle rapidly, with minimal damage by oxidation. Cardiac relaxing proteins inhibit actomyosin ATPase activity in the presence of ethyleneglycoltetraacetic acid (EGTA), and permit graded stimulation by Ca 2+. This stimulation is independent of preexisting inhibition, and greater than that obtained with skeletal proteins. Characteristics of Scatchard plots for Ca 2+ binding suggest that troponin contains one class of sites which interact at high fractional occupancy. Interaction appears to be enhanced by tropomyosin. Mean values for the estimated maximum affinity and capacity of six canine cardiac troponin preparations were: 4.92·10 6 M −1, and 21.58·10 −6 moles·g −1. Values for skeletal troponin were not significantly different. Native tropomyosin bound about half as much Ca 2+ per g, with maximum affinity the same as troponin. Pure tropomyosin bound no Ca 2+. Cardiac and skeletal proteins differ in that the former are much more labile, and more readily influenced by ions and drugs.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA) - Bioenergetics
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