title: Tryptic cleavage and substructure of bovine cardiac myosin subfragment 1.
abstract: The method of limited tryptic proteolysis has been used to compare and contrast the substructure of bovine cardiac myosin subfragment 1 (S-1) to that of skeletal myosin S-1. While tryptic cleavage of cardiac S-1, like that of skeletal S-1, yields three fragments, the 25K, 50K, and 20K peptides, the digestion of cardiac S-1 proceeds at a 2-fold faster rate. The increased rate of cleavage is due entirely to an order of magnitude faster rate of cleavage at the 25K/50K junction of cardiac S-1 compared to that of skeletal, with approximately equal rates of cleavage at the 50K/20K junctions. Actin inhibits the tryptic attack at this latter junction, but its effect is an order of magnitude smaller for the cardiac than for the skeletal S-1. Furthermore, the tryptic susceptibility of the 50K/20K junction of cardiac S-1 in the acto-S-1 complex is increased in the presence of 2 mM MgADP. This effect is not due to partial dissociation of the cardiac acto-S-1 complex by MgADP. Our results indicate that in analogy to skeletal S-1, the cardiac myosin head is organized into three protease-resistant fragments connected by open linker peptides. However, the much faster rate of tryptic cleavage of the 25K/50K junction and also the greater accessibility of the 50K/20K junction in the cardiac acto-S-1 complex indicate substructural differences between cardiac and skeletal S-1.
mesh_terms: D000199:Actins / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D009132:Muscles / Q000032:analysis; D009206:Myocardium / Q000032:analysis; D015879:Myosin Subfragments; D009218:Myosins / Q000302:isolation & purification*; D010446:Peptide Fragments / Q000302:isolation & purification*; D014357:Trypsin; D014361:Trypsin Inhibitors
chemical_list: D000199:Actins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D014361:Trypsin Inhibitors; D014357:Trypsin; D009218:Myosins