Tryptic digestion as a probe of myosin S-1 conformation.
One of the products of the limited tryptic hydrolysis of chymotryptic myosin subfragment 1 is the 27,000-dalton NH2-terminal fragment. This fragment is generated by two parallel routes from either the 75,000- or 95,000-dalton peptide of the heavy chain: (i) through a 20,500-dalton precursor or (ii) directly without participation of a precursor. Lowering of pH and temperature and increasing of ionic strength inhibited route i digestion in comparison to route ii. MgATP and its derivatives in millimolar concentration substantially suppressed route i digestion. Suppression of route i digestion depended on the concentration of MgATP. It occurred after a lag phase when the ratio of MgATP to subfragment 1 concentrations was greater than 0.5. In contrast, the MgATP-induced increase in tryptophan fluorescence of myosin subfragment 1 appeared without a lag phase. The generation of the 27,000-dalton fragment by either route was not affected by F-actin however, the suppression of route i digestion induced by MgADP was abolished when myosin subfragment 1 was in ternary complex with  actin and MgADP. We conclude that the 27,000/50,000-dalton hinge region is a flexible domain of the myosin head and that conformation of this region is sensitive to the presence of nucleotides and actin and to variations in ambient factors.
D000199:Actins / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D015879:Myosin Subfragments; D009218:Myosins; D009994:Osmolar Concentration; D010446:Peptide Fragments; D011487:Protein Conformation / Q000187:drug effects; D013696:Temperature; D014357:Trypsin
D000199:Actins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D014357:Trypsin; D009218:Myosins