LIMITED TRYPTIC CLEAVAGE OF CHYMOTRYPTIC S-1 - APPROACH TO THE CHARACTERIZATION OF THE ACTIN SITE IN MYOSIN HEADS

Limited tryptic proteolysis of S-1 (A1+A2) or S-1 (A1) and S-1 (A2) converts the heavy chain into 3 fragments of Mr = 27K-50K-20K. As a result the actin-stimulated ATPase activity of the fragmented heads is lost. When the digestion is performed using the complex F-actin-S-1, this ATPase activity is completely preserved and the heavy chain is split into only 2 fragments of Mr = 27K-70K. The specific protection by F-actin of the -COOH terminal region of the heavy chain at the joint 50K-20K against tryptic cleavage and loss of activity suggests that this part of the head can be involved in actin binding site and/or Mg2+ ATP hydrolysis by the acto-S-1 complex. © 1979.