Identification of the site important for the actin-activated MgATPase activity of myosin subfragment-1.

The lysine-rich sequence (-KKGGKKK-) located at the 50,000/20,000 Mr junction of myosin subfragment-1 (S-1) was cleaved by endoprotease Arg-C or by trypsin in the presence of ATP and an equimolar amount of actin. Under these conditions, cleavage by Arg-C was between the first and second lysine residues, whereas cleavage by trypsin was between the third and fourth lysine residues. The actin-activated MgATPase activity of the S-1 cleaved by Arg-C was almost the same as native S-1, but S-1 cleaved by trypsin showed markedly reduced ATPase activity.