%0 Journal Article
%T Tropomyosin Period 3 Is Essential for Enhancement of Isometric Tension in Thin Filament-Reconstituted Bovine Myocardium
%A Masataka Kawai
%A Xiaoying Lu
%A Sarah E. Hitchcock-DeGregori
%A Kristen J. Stanton
%A Michael W. Wandling
%J Journal of Biophysics
%D 2009
%I Hindawi Publishing Corporation
%R 10.1155/2009/380967
%X Tropomyosin (Tm) consists of 7 quasiequivalent repeats known as “periods,” and its specific function may be associated with these periods. To test the hypothesis that either period 2 or 3 promotes force generation by inducing a positive allosteric effect on actin, we reconstituted the thin filament with mutant Tm in which either period 2 (¦¤2Tm) or period 3 (¦¤3Tm) was deleted. We then studied: isometric tension, stiffness, 6 kinetic constants, and the pCa-tension relationship. N-terminal acetylation of Tm did not cause any differences. The isometric tension in ¦¤2Tm remained unchanged, and was reduced to ¡«60% in ¦¤3Tm. Although the kinetic constants underwent small changes, the occupancy of strongly attached cross-bridges was not much different. The Hill factor (cooperativity) did not differ significantly between ¦¤2Tm (1.79 ¡À 0.19) and the control (1.73 ¡À 0.21), or ¦¤3Tm (1.35 ¡À 0.22) and the control. In contrast, pCa50 decreased slightly in ¦¤2Tm (5.11 ¡À 0.07), and increased significantly in ¦¤3Tm (5.57 ¡À 0.09) compared to the control (5.28 ¡À 0.04). These results demonstrate that, when ions are present at physiological concentrations in the muscle fiber system, period 3 (but not period 2) is essential for the positive allosteric effect that enhances the interaction between actin and myosin, and increases isometric force of each cross-bridge.
%U http://www.hindawi.com/journals/jbp/2009/380967/