Modulation of the actin-activated adenosine triphosphatase activity of myosin by tropomyosin from vascular and gizzard smooth muscles

Abstract

Tropomyosins from bovine aorta and pulmonary artery exhibit identical electrophoretic patterns in sodium dodecyl sulfate but differ from tropomyosins of either chicken gizzard or rabbit skeletal muscle. Each of the four tropomyosins binds readily to skeletal muscle F-actin as indicated by their sedimentation with actin and by their ability to maximally stimulate or inhibit actin-activated ATPase activity at a molar ratio of one tropomyosin per seven actin monomers. Smooth and skeletal muscle tropomyosins differ in their effects on activity of skeletal myosin or heavy meromyosin (HMM); the former can enhance activity under conditions in which the latter inhibits. Gizzard and arterial tropomyosins are usually equally effective in stimulating ATPase activity of skeletal acto-HMM, but at high concentrations of Mg2+ gizzard tropomyosin is more effective, a result that cannot be attributed to differences in the binding of the two tropomyosins to F-actin. The effects of tropomyosin also depend on the type of myosin; tropomyosin enhances activity of gizzard myosin under conditions in which it inhibits that of skeletal myosin. Increasing the pH or the Mg2+ concentration can reverse the effect of tropomyosin on actin-stimulated ATPase activity of skeletal HMM from activation to inhibition, but this reversal is not found with gizzard myosin. Activity in the absence of tropomyosin is independent of pH, and the loss of activation with increasing pH is not accompanied by loss of binding of tropomyosin to actin.

Relationship between alternatively spliced exons and functional domains in tropomyosin.

“…The activation in the presence of Ca2" was similar even though TM isoforms often differ quantitatively with regard to this phenomenon (29,41). The state of the thin filament or the ability of the myosin S1 to influence the state of the thin filament does not seem to be affected by the identity of TM exons 2 and 9.…”

Effects of hypoxia on high‐energy phosphagen content, energy metabolism and isometric force in guinea‐pig taenia caeci.

“…The calcium sensitivity of the smooth muscle actin-myosin ATPase and tension in skinned fibres was reported to be reduced by a decrease in pH (Mrwa, Achtig & Riiegg, 1974), though recent reports appear to limit the generality of this finding (Jino, 1981;Sparrow, Pfitzer, Gagelmann & Ruegg, 1984;Yamaguchi, Ver, Carlos & Seidel, 1984;Arheden, Arner & Hellstrand, 1989). In this and previous work (Ishida et al 1984) it was shown that a 10-fold increase in glucose under hypoxic conditions elevated lactate content and lactate production while at the same time elevating the level of isometric force.…”

Effect of pH on the rate of myosin head detachment in molluscan catch muscle: are myosin heads involved in the catch state?

“…By contrast, in some smooth muscles, opposite pH effects on maximum tension were observed (Spurway and Wray, 1987;Smith et al, 1998). For cardiac muscle and smooth muscle, troponin C (Ding et al, 1996) and tropomyosin (Yamaguchi et al, 1984), respectively, were considered as pH sensors, which influence actin-myosin interaction.…”