Regulation of the adenosinetriphosphatase activity of cross-linked actin-myosin subfragment 1 by troponin-tropomyosin.
Chalovich and Eisenberg [Chalovich, J. M., & Eisenberg, E. (1982) J. Biol. Chem. 257, 2432-2437] have suggested that at low ionic strength, troponin-tropomyosin regulates the actomyosin ATPase activity by inhibiting a kinetic step in the actomyosin ATPase cycle rather than by blocking the binding of myosin subfragment 1 (S-1) to actin. This leads to the prediction that troponin-tropomyosin should inhibit the ATPase activity of the complex of actin and S-1 (acto . S-1) even when S-1 is cross-linked to actin. We now find that the ATPase activity of cross-linked actin . S-1 prepared under milder conditions than those used by Mornet et al. [Mornet, D., Bertrand, R., Pantel, P., Audemard, E., & Kassab, R. (1981) Nature (London) 292, 301-306] is inhibited 90% by troponin-tropomyosin in the absence of Ca2+. At mu = 18 mM, 25 degrees C, the ATPase activity of this cross-linked preparation is only about 2-fold greater than the maximal actin-activated ATPase activity of S-1 obtained with regulated actin in the absence of Ca2+. At physiological ionic strength, the ATPase activity of this cross-linked actin . S-1 preparation is inhibited about 95% by troponin-tropomyosin. Since cross-linked S-1 behaves kinetically like S-1 in the presence of infinite actin concentration, it is very unlikely that inhibition of the ATPase activity of cross-linked actin . S-1 is due to blocking of the binding of S-1 to actin. Therefore, these results are in agreement with the suggestion that troponin-tropomyosin regulates primarily by inhibiting a kinetic step in the ATPase cycle.
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D000199:Actins / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002250:Carbon Radioisotopes; D007460:Iodoacetamide / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D009132:Muscles / Q000378:metabolism; D015879:Myosin Subfragments; D009218:Myosins / Q000302:isolation & purification / Q000378:metabolism*; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000302:isolation & purification / Q000378:metabolism*; D011817:Rabbits; D014335:Tropomyosin / Q000378:metabolism*; D014336:Troponin / Q000378:metabolism*
D000199:Actins; D002250:Carbon Radioisotopes; D046911:Macromolecular Substances; D015879:Myosin Subfragments; D010446:Peptide Fragments; D014335:Tropomyosin; D014336:Troponin; D000251:Adenosine Triphosphatases; D009218:Myosins; D007460:Iodoacetamide