The effect of tropomyosin on force and elementary steps of the cross-bridge cycle in reconstituted bovine myocardium.

The role of tropomyosin (Tm) in the elementary steps of the cross-bridge cycle in bovine myocardium was investigated. The thin filament was selectively removed using gelsolin (thin filament severing protein), and the actin filament was reconstituted from G-actin. Tm was further reconstituted without troponin (Tn), and the kinetic constants of the elementary steps of the cross-bridge cycle were deduced using sinusoidal analysis at pCa (1) In genetic epidemiology, describes the situation in which a particular allele is found either significantly more or significantly less frequently in a group of affected individuals than would be expected from the frequency of the allele in the general population from which the affected individuals were drawn; not to be confused with linkage.(2) In dysmorphology, a group of abnormalities of unknown etiology and pathogenesis that is seen together more often than would be expected by chance.

" data-original-title="Association" data-html="true" data-trigger="foucs">association constant of MgATP to cross-bridges (K(1)) after reconstitution of Tm was 20.7 +/- 2.3 mm(-1), which was about 2 x the control (untreated) myocardium (9.1 +/- 1.3 mm(-1)). Following reconstitution of Tm, the equilibrium constant of the cross-bridge detachment step (K(2)), the phosphate (P(i)) association constant (K(5)) and the equilibrium constant of the force-generation step (K(4)), which significantly changed in the actin filament-reconstituted myocardium, recovered to those of the control myocardium. Active tension after reconstitution of Tm was 0.69 x the control myocardium, a value between the control (1.00 x) and the actin filament-reconstituted myocardium (0.59 x). Tm-reconstituted myocardium was further reconstituted with Tn, and the effect of MgATP on the rate constants (K(1), K(2)) was studied. Following reconstitution with Tn, the myocardium regained the Ca(2+)-sensitivity and the active tension became 0.83 x the control myocardium. In addition, K(1) recovered to the value of the control myocardium with Tn reconstitution. These results indicate that both Tm and Tn enhance the force generated by each cross-bridge, and that Tm is primarily responsible for the change in the kinetic constants of the elementary steps of the cross-bridge cycle.

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