title: Evidence for head-head interactions in myosin from cardiac and skeletal muscles.
abstract: 1. Binding of MG-ADP to both heart and fast skeletal myosin was found with 3 methods to proceed in 2 steps. One mole of MG-ADP binds with high affinity (K approximately equal to 10(6) M-1) and subsequently a second with lower affinity (K approximately equal to 10(2)-10(4) M-1) per myosin. Only one mole of MG-ADP was found to bind with the high affinity to isolated myosin heads. This implies that binding of MG-ADP to intact myosin exhibits negative cooperativity. 2. When a nucleotide is bound, the 2 heads of a single myosin molecule adopt different conformations since on each head a different type of essential thiol group was found to be the most reactive towards N-ethylmaleimide. In the presence of MG-pyrophosphate a thiol-1 is the most reactive essential group in both heads. Therefore, the nucleoside moiety seems to be required for this latter type of head-head interaction.
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D011756:Diphosphates / Q000378:metabolism; D005033:Ethylmaleimide / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D008968:Molecular Conformation; D009132:Muscles / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D009711:Nucleotides / Q000378:metabolism; D011485:Protein Binding; D011817:Rabbits; D013552:Swine
chemical_list: D011756:Diphosphates; D009711:Nucleotides; D000244:Adenosine Diphosphate; D009218:Myosins; D008274:Magnesium; D005033:Ethylmaleimide