INTERACTION OF MYOSIN SUBFRAGMENT-1 WITH ACTIN .2. LOCATION OF THE ACTIN BINDING-SITE IN A FRAGMENT OF SUBFRAGMENT-1 HEAVY-CHAIN

The heavy chain of subfragment-1 prepared by chymotrypsin treatment had a molecular weight of about 96 K. The heavy chain was split into 26 K, 50 K, and 21 K fragments by trypsin. When the trypsin-treated subfragment-1 was cross-linked with dimethyl suberimidate, cross-linked products of 26 K, 50 K, and 21 K fragments and of 50 K and 21 K fragments appeared, but there was little cross-linked product of 26 K and 50 K fragments or of 26 K and 21 K fragments. When the cross-linking experiments were carried out in the presence of actin, a new band appeared and the amount of cross-linked product of 26 K, 50 K, and 21 K fragments decreased by about 50%. The molecular weight of the new band was lower than that of the cross-linked product of 26 K, 50 K, and 21 K fragments, and higher than that of the dimer of actin. Based on this and some other results, we suggest that this band represented a cross-linked product of actin and the 50 K fragment. We also suggest that the decrease in the amount of cross-linked product of 26 K, 50 K, and 21 K fragments reflected the conformational change in subfragment-1 due to the binding of actin. © 1979, by the Japanese Biochemical Society.