title: Actin-induced local conformational change in the myosin molecule. II. Conformational change around the S2 thiol group related to the essential intermediate of ATP hydrolysis.
abstract: The effect of F-actin on the conformation around a specific thiol group, S2, in heavy meromyosin was investigated. The extent of the change was estimated from the residual activity of Ca2+-ATPase after modifying the thiol with N-ethylmaleimide (NEM). Experiments were carried out with a modified heavy meromyosin (HMM), in which S1 had been blocked with NEM, to observe the reactivity of S2 alone. 1. F-Actin markedly increased the ATP-induced conformational change around S2, but did not affect the adenylyl imidodiphosphate (AMPPNP)-induced change, and markedly supressed the adenylyl methylenediphosphate (AMPPCP)-induced change. 2. The initial burst of HMM ATPase was retained after the modification of S1. Replacement of Mg2+ with Mn2+ in the medium reduced the cooperative action of F-actin and ATP with concomitant loss of the initial burst. 3. Nevertheless, F-actin was capable of activating the steady-state ATPase activity of HMM even in the presence of Mn2+. 4. The degree of activation by F-actin of the ATP-induced increase in the reactivity of S2 did not parallel that of the steady-state ATP splitting, when the KCl concentration of the medium was varied. The results indicate that the actin-induced local conformational change in the S2 region is related to an energized state of the myosin molecule caused by Mg2+-ATP, but is apparently not related to the actin-activated steady-state ATPase activity.
mesh_terms: D000199:Actins / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D005033:Ethylmaleimide / Q000494:pharmacology; D006868:Hydrolysis; D046911:Macromolecular Substances; D008345:Manganese / Q000494:pharmacology; D015879:Myosin Subfragments / Q000378:metabolism; D009218:Myosins; D011189:Potassium Chloride / Q000494:pharmacology; D011487:Protein Conformation; D011817:Rabbits; D013438:Sulfhydryl Compounds / Q000378:metabolism*
chemical_list: D000199:Actins; D046911:Macromolecular Substances; D015879:Myosin Subfragments; D013438:Sulfhydryl Compounds; C005147:5'-adenylyl (beta,gamma-methylene)diphosphonate; D008345:Manganese; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D009218:Myosins; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D005033:Ethylmaleimide