title: 18O-exchange catalyzed by myosin, heavy meromyosin, heavy meromyosin subfragment 1 and their complexes with actin.
abstract: Myosin, HMM and HMM S1 catalyze 18O-exchange between P1 and H218O of the medium at an intermediate stage of ATP hydrolysis ("intermediate 18O-exchange") in the presence of Mg2+. Natural complexes of actomyosin and acto-HMM S1 do not catalyze intermediate 18O-exchange but facilitate "direct" or "medium" 18O-exchange (KH2P18O4 in equilibrium H2O) even without ATP. Reconstituted complexes of actomyosin, acto-HMM, acto-HMM S1, PABC-HMM S1, congo-myosin and TNP-myosin do not catalyze direct 18O-exchange in the presence of Mg2+ and absence of ATP. From the data obtained a hypothetical sequence of phosphorylation and 18O-exchange reactions in myofibril action has been suggested.
mesh_terms: D000199:Actins; D000251:Adenosine Triphosphatases; D000255:Adenosine Triphosphate; D001665:Binding Sites; D006868:Hydrolysis; D015879:Myosin Subfragments; D009218:Myosins; D010103:Oxygen Isotopes
chemical_list: D000199:Actins; D015879:Myosin Subfragments; D010103:Oxygen Isotopes; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D009218:Myosins