Effects of tropomyosin internal deletion Delta23Tm on isometric tension and the cross-bridge kinetics in bovine myocardium.
Tropomyosin (Tm) spans seven actin monomers and contains seven quasi-repeating, loosely similar regions, 1-7. Deletion of regions 2-3 decreases the in vitro sliding speed of synthetic filaments of actin-Tm-Troponin (Tn), and weakens Tm binding to the actin-myosin subfragment 1 (S1) complex (acto-S1). The thin filament was selectively removed from bovine myocardium by gelsolin, and the actin filament was reconstituted, followed by further reconstitution with Tm and Tn. In this reconstitution, full-length Tm (control) was compared with Tm internal deletion mutant Delta23Tm, which lacks residues 47-123 (regions 2-3). The effects of phosphate, MgATP, MgADP and Ca2+ were studied in Tm-reconstituted myocardium and Delta23Tm-reconstituted myocardium at pH 7.00 and 25 degrees C. In Delta23Tm, both isometric tension and stiffness were about 40 % of the control. The Hill factor with Delta23Tm, deduced from the pCa-tension plot, was 1.4 times that of the control, but the Ca2+ sensitivity was the same. Sinusoidal analysis indicated that the cross-bridge number in force-generating states was not decreased with Delta23Tm. We conclude that the thin filament cooperativity is increased with Delta23Tm, presumably because of the increased density of the Ca2+-binding sites. We further conclude that tension per cross-bridge is 40 % of control and stiffness per cross-bridge is 40 % of control in Delta23Tm. These results are consistent with the idea that Tm modifies the actin-myosin interface so as to increase the stereospecific interaction between moieties of actin and myosin. In Delta23Tm, the interface may not have a perfect stereospecific match so that the tension- and stiffness-generating capacity is greatly diminished.
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000465:Algorithms; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D004548:Elasticity / Q000187:drug effects; D004591:Electrophoresis, Polyacrylamide Gel; D017353:Gene Deletion; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D007537:Isometric Contraction / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D009124:Muscle Proteins / Q000032:analysis; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D010710:Phosphates / Q000494:pharmacology; D014335:Tropomyosin / Q000235:genetics / Q000502:physiology*
D046911:Macromolecular Substances; D009124:Muscle Proteins; D010710:Phosphates; D014335:Tropomyosin; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D002118:Calcium