Heterogeneity in enzymatic sites of heavy meromyosin shown by measuring F-actin-inactivated hydrolysis of beta-naphthyl triphosphate.
Enzymatic characteristics of heavy meromyosin (HMM) were investigated by measuring beta-naphthyl triphosphate (beta-NapP3) hydrolysis in the presence and absence of F-actin. beta-NapP3 hydrolysis by HMM was inactivated by F-actin in the presence of Mg ions; in the presence of sufficient F-actin, the activity was about one-half of that in the absence of F-actin. In the presence of Ca ions the activity disappeared almost completely on addition of sufficient F-actin. Two different values of the Michaelis constant (Km) were obtained from the data for beta-NapP3 hydrolysis by HMM in the presence of Mg ions; one of them vanished in the presence of sufficient F-actin, and only one Km value was obtained in the presence of Ca ions. These results suggest the existence of two distinct enzymatic sites in HMM, one inactivated by F-actin in the presence of Mg or Ca ions, the other inactive in the presence of Ca ions but active in the presence of Mg ions and not influenced by F-actin. Use of subfragment-1(A1) (S-1(A1)) and S-1(A2) instead of HMM confirmed that these enzymatic characteristics are not due to a difference in the alkali light chains on myosin heads.
D000199:Actins / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D006868:Hydrolysis; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D015879:Myosin Subfragments / Q000378:metabolism*; D010755:Organophosphates; D009943:Organophosphorus Compounds
D000199:Actins; D015879:Myosin Subfragments; D010755:Organophosphates; D009943:Organophosphorus Compounds; C011943:beta-naphthyl triphosphate; D008274:Magnesium; D002118:Calcium