The mechanism for the inhibition of actin-activated ATPase of smooth muscle heavy meromyosin by calponin.
Calponin, an actin-binding protein, inhibited the acto-heavy meromyosin (HMM) MgATPase and lowered the binding of HMM to actin. The amount of calponin bound to actin or tropomyosin-actin was the same when the ATPase was inhibited 80-90%. While the KATPase was diminished only less than 2-fold in the presence of calponin, the Vmax was decreased 6-fold and 2-fold with actin and tropomyosin-actin, respectively. A comparison of the kinetic constants for the ATP hydrolysis obtained in the presence of actin-calponin and tropomyosin-actin-calponin revealed that the tropomyosin augmented the Vmax 5-fold from the inhibited level, but there was no effect on the KATPase.
Horiuchi
K Y
KY
Department of Pathobiology, University of Pennsylvania, Philadelphia 19104.
Chacko
S
S
D000199:Actins / Q000378:metabolism*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors*; D002135:Calcium-Binding Proteins / Q000378:metabolism / Q000494:pharmacology*; D002645:Chickens; D004789:Enzyme Activation; D005895:Gizzard, Avian / Q000378:metabolism; D007700:Kinetics; D008840:Microfilament Proteins; D009124:Muscle Proteins / Q000494:pharmacology; D009130:Muscle, Smooth / Q000378:metabolism*; D015879:Myosin Subfragments / Q000037:antagonists & inhibitors*; D011485:Protein Binding; D000096985:Calponins
D000199:Actins; D017301:Ca(2+) Mg(2+)-ATPase; D002135:Calcium-Binding Proteins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D015879:Myosin Subfragments; D000096985:Calponins