Dependence on Ca2+ and tropomyosin of the actin-activated ATPase activity of phosphorylated gizzard myosin in the presence of low concentrations of Mg2+.

Nag, Sumitra; Seidel, John C.

doi:10.1016/s0021-9258(18)32430-x

Cited by 33 publications

(11 citation statements)

References 43 publications

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“…Evidence exists, however, that a second regulatory system involving Ca 2+ may operate in smooth muscle (32). The nature of this system is not known at present but may involve direct Ca 2÷binding to the myosin (33) or thin filament regulatory proteins (34,35). The Nitella system should prove useful in determining whether Ca 2+ plays a secondary or modulatory role by interacting directly with smooth muscle myosin.…”

Section: Discussionmentioning

confidence: 99%

Light chain phosphorylation regulates the movement of smooth muscle myosin on actin filaments.

Sellers¹,

Spudich²,

Sheetz³

1985

The Journal of Cell Biology

120

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In smooth muscles there is no organized sarcomere structure wherein the relative movement of myosin filaments and actin filaments has been documented during contraction. Using the recently developed in vitro assay for myosin-coated bead movement (Sheetz, M.P., and J.A. Spudich, 1983, Nature (Lond.)., 303:31-35), we were able to quantitate the rate of movement of both phosphorylated and unphosphorylated smooth muscle myosin on ordered actin filaments derived from the giant alga, Nitella. We found that movement of turkey gizzard smooth muscle myosin on actin filaments depended upon the phosphorylation of the 20-kD myosin light chains. About 95% of the beads coated with phosphorylated myosin moved at velocities beween 0.15 and 0.4/~m/s, depending upon the preparation. With unphosphorylated myosin, only 3% of the beads moved and then at a velocity of only ~0.01-0.04/~m/s. The effects of phosphorylation were fully reversible after dephosphorylation with a phosphatase prepared from smooth muscle. Analysis of the velocity of movement as a function of phosphorylation level indicated that phosphorylation of both heads of a myosin molecule was required for movement and that unphosphorylated myosin appears to decrease the rate of movement of phosphorylated myosin. Mixing of phosphorylated smooth muscle myosin with skeletal muscle myosin which moves at 2/~m/s resulted in a decreased rate of bead movement, suggesting that the more slowly cycling smooth muscle myosin is primarily determining the velocity of movement in such mixtures.

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Section: Discussionmentioning

confidence: 99%

Light chain phosphorylation regulates the movement of smooth muscle myosin on actin filaments.

Sellers¹,

Spudich²,

Sheetz³

1985

The Journal of Cell Biology

120

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“…In the absence of KC1, Mg2+ concentrations approaching 5 mM are necessary for inhibition of acto-S-1 ATPase activity by skeletal tropomyosin and for the binding of tropomyosin to F-actin (Eaton et al, 1975;Wegner, 1979;Yang et al, 1979). Smooth muscle tropomyosins can activate the ATPase activity of acto-HMM at concentrations of MgCI2 equal to or less than that of ATP (Figure 4; Nag & Seidel, 1983), but activation at these low concentrations may be in part attributable to the presence of 50 mM NaCl in the assay medium, which reduces the concentration of Mg2+ required for tropomyosin binding (Eaton et al, 1975;Yang et al" 1979). Increasing the concentration of MgCl2-or the pH as discussed below-tends to reverse the effect to tropomyosin from stimulation to inhibition, as previously observed with cardiac tropomyosin (Leger et al, 1979).…”

Section: Discussionmentioning

confidence: 99%

“…Smooth muscle tropomyosin stimulates rather than inhibits activity (Chacko et al, 1977;Hartshorne et al, 1977;Ebashi et al, 1977; Sobieszek & Small, 1977) and according to most reports plays no direct role in Ca2+-dependent activation of actomyosin ATPase activity, which requires enzymatic phosphorylation of the myosin light chain (Chacko et al, 1977; Gorecka et al, 1976;Sobieszek & Small, 1976). A possible link to Ca2+-dependent regulation in smooth muscle is suggested by the requirement of both Ca2+ and tropomyosin for optimal actin-activated ATPase activity with phosphorylated smooth muscle myosin (Chacko et al, 1977;Chacko & Rosenfeld, 1982; Nag & Seidel, 1983), while a report of a similar requirement with unphosphorylated myosin (Ebashi et al, 1977) has not yet been confirmed.…”

mentioning

confidence: 99%

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

Yamaguchi¹,

Vér²,

Carlos³

et al. 1984

Biochemistry

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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.

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“…Despite these uncertainties concerning the function of tropomyosin in smooth muscle, it has been observed in many laboratories, and with proteins from several source tissues, that tropomyosin activates actomyosin ATPase activity (Hartshorne et al, 1977; Sobieszek & Small, 1977;Chacko, 1981; Nag & Seidel, 1983). Under certain conditions, both smooth and skeletal muscle tropomyosins activate ATPase activity (Hartshorne et al, 1977;Chacko, 1981), although some differences between tropomyosins from the two muscle types have been observed (Sobieszek & Small, 1981;Yamaguchi et al, 1984).…”

mentioning

confidence: 99%

“…Under certain conditions, both smooth and skeletal muscle tropomyosins activate ATPase activity (Hartshorne et al, 1977;Chacko, 1981), although some differences between tropomyosins from the two muscle types have been observed (Sobieszek & Small, 1981;Yamaguchi et al, 1984). In addition, both skeletal and smooth muscle actins can form actomyosin hybrids with smooth muscle myosin capable of activation by tropomyosin (Nag & Seidel, 1983).…”

mentioning

confidence: 99%

Interaction of smooth muscle tropomyosin and smooth muscle myosin. Effect on the properties of myosin

Merkel¹,

Ikebe²,

Hartshorne³

1989

Biochemistry

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Several techniques were used to investigate the possibility that smooth muscle tropomyosin interacts with smooth muscle myosin. These experiments were carried out in the absence of actin. The Mg2+-ATPase activity of myosin was activated by tropomyosin. This was most marked at low ionic strength but also occurred at higher ionic strength with monomeric myosin. For myosin and HMM, the activation of Mg2+-ATPase by tropomyosin was greater at low levels of phosphorylation. There was no detectable effect of tropomyosin on the Mg2+-ATPase activity of S1. The KCl dependence of myosin viscosity was influenced by tropomyosin, and in the presence of tropomyosin, the 6S to 10S transition occurred at lower KCl concentrations. From the viscosity change, an approximate stoichiometry of 1:1 tropomyosin to myosin was estimated. The phosphorylation dependence of viscosity, which reflects the 10S-6S transition, also was altered in the presence of tropomyosin. An interaction between myosin and tropomyosin was detected by fluorescence measurements using tropomyosin labeled with dansyl chloride. These results indicate that an interaction occurs between myosin and tropomyosin. In general, the interaction is favored at low ionic strength and at low levels of phosphorylation. This interaction is not expected to be competitive with the formation of the actin-tropomyosin complex, but the possibility is raised that a direct interaction between myosin and tropomyosin bound to the thin filament could modify contractile properties in smooth muscle.

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Dependence on Ca2+ and tropomyosin of the actin-activated ATPase activity of phosphorylated gizzard myosin in the presence of low concentrations of Mg2+.

Cited by 33 publications

References 43 publications

Light chain phosphorylation regulates the movement of smooth muscle myosin on actin filaments.

Light chain phosphorylation regulates the movement of smooth muscle myosin on actin filaments.

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

Interaction of smooth muscle tropomyosin and smooth muscle myosin. Effect on the properties of myosin

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