Effect of divalent cations on the proteolysis of vertebrate and invertebrate muscle myosin.

Analysis by SDS-polyacrylamide gel electrophoresis of the products of alpha-chymotryptic digestion of lobster abdominal muscle myosin has shown that the presence or absence of Ca2+ during proteolysis does not have a major influence on the site of cleavage of the parent molecule, as it does for proteolysis of vertebrate muscle myosin. By following H+ liberation on the pH-stat during proteolysis, it has been found that the divalent cation only suppresses digestion of lobster myosin by about 15% as compared with proteolysis in the absence of Ca2+. Additionally, the subfragment-1-like species made by alpha-chymotryptic digestion of lobster myosin at low ionic strength is much more susceptible to degradation by trypsin than is vertebrate muscle myosin sub-fragment-1, in accordance with the relative susceptibilities of the parent molecules to similar degradation.