title: [Several peculiarities of the purine-base fixation of the substrate in the active sites of myosin Ca2+-ATPase].
abstract: A comparative study of kinetic parameters (Km and V) of hydrolysis by heavy meromyosin of several synthetic ATP analogs with substituents at positions N(1) and N(C6) of the purine ring was carried out. Analysis of changes in the Km values suggests that the purine base of ATP is fixed in the active center due to the formation of a hydrogen bond between N1 and the proton donor group of the protein as well as between the 6-NH2-amino group of the nucleotide and the proton acceptor group of the protein. It was shown that the rate of catalytic conversion of the substrate is determined by the mode of binding of its purine ring. Depending on the properties of the substituent radical, the latter either prevents the binding by causing little or no increase in the rate of hydrolysis or causes the displacement of the whole substrate molecule in the active center, which leads to the deceleration of hydrolysis.
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D006868:Hydrolysis; D066298:In Vitro Techniques; D007293:Inosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D009132:Muscles / Q000201:enzymology*; D015879:Myosin Subfragments / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D011687:Purines / Q000378:metabolism*; D011817:Rabbits; D013379:Substrate Specificity
chemical_list: D015879:Myosin Subfragments; D010446:Peptide Fragments; D011687:Purines; D007293:Inosine Triphosphate; D000255:Adenosine Triphosphate; D009218:Myosins; D000252:Calcium-Transporting ATPases
vernacular_title: O nekotorykh osobennostiakh fiksatsii purinovogo osnovaniia substrata v aktivnom tsentre Ca2+-ATPazy miozina.