Powerful activation of skeletal muscle actomyosin ATPase by goniodomin A is highly sensitive to troponin/tropomyosin complex.
Goniodomin A has been shown to cause the conformational change of actin to modify actomyosin ATPase activity. Goniodomin A induced a potent stimulation of the actomyosin ATPase activities of the actin-myosin reconstituted system and natural actomyosin in the range of 10(-8) to 10(-7) M. When the concentration was increased above 10(-7) M, actomyosin ATPase activity was decreased. Interestingly, the troponin/tropomyosin complex caused a concentration-dependent inhibition of the goniodomin A-induced stimulation of actomyosin ATPase activity. In the presence of a high concentration of the troponin/tropomyosin complex, goniodomin A decreased actomyosin ATPase activity in a concentration-dependent manner. The enhancement of the ATPase activity of troponin/tropomyosin-free natural actomyosin by goniodomin A was larger than that obtained with natural actomyosin. Goniodomin A at lower concentrations enhanced the superprecipitation of natural actomyosin but decreased it at higher concentrations. The ATPase activity of skeletal muscle myofibrils and the contractile response of skinned fibers to Ca(2+) were never activated and were decreased by this compound, suggesting an inhibition by the troponin/tropomyosin complex. In the far ultraviolet circular dichroism, goniodomin A above 10(-8) M increased the negative ellipticity at 220 nm, suggesting an increase in the alpha-helical content of actin. These results suggest that goniodomin A increases and decreases actomyosin ATPase activity, probably through the stimulatory and inhibitory sites on actin, respectively. It is also suggested that the troponin/tropomyosin complex binds to actin to inhibit the goniodomin A-induced enhancement of actomyosin ATPase activity, probably by affecting the stimulatory site on the molecule.
Matsunaga
K
K
Department of Pharmaceutical Molecular Biology, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Aramaki, Sendai, Japan.
Nakatani
K
K
Murakami
M
M
Yamaguchi
K
K
Ohizumi
Y
Y
D000199:Actins / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D002942:Circular Dichroism; D004987:Ethers / Q000494:pharmacology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D018942:Macrolides / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects; D018482:Muscle, Skeletal / Q000201:enzymology*; D009210:Myofibrils / Q000187:drug effects / Q000201:enzymology; D009218:Myosins / Q000378:metabolism*; D011817:Rabbits; D014335:Tropomyosin / Q000494:pharmacology*; D014336:Troponin / Q000494:pharmacology*
D000199:Actins; D004987:Ethers; D018942:Macrolides; D014335:Tropomyosin; D014336:Troponin; C042260:troponin-tropomyosin complex; C059668:goniodomin A; D009218:Myosins