Abstract
Subfragment one (S1) from squid mantle myosin was subjected to limited proteolysis and analyzed for peptide composition by SDS-polyacrylamide gel electrophoresis. Tryptic digestion of S1 in the absence of actin revealed that l00 kilo daltons (Kd) heavy chain gave rise to three peptides whose molecular weights were 47, 27, and 23 Kd. However, the digestion of S1 in the presence of actin resulted in only two peptides of 70 and 27 Kd. The size and composition of these peptides were similar to those from rabbit skeletal S1. Chymotryptic digestion of S1 re-moved regulatory light chain but not essential light chain, decreased the molecular weight of heavy chain from l00 Kd to 90 Kd. When a limited digest of S1 with trypsin was further digested by chymotrypsin, 47 and 27 Kd peptides with essential light chain were unaffected, while both re-gulatory light chain and 23 Kd peptide notably disappeared. The limited digest of squid Sl with trypsin was trinitrophenylated with 2, 4, 6-trinitro benzene sulfonate either in the presence or absence of inorganic pyrophosphate and applied to a Bio-Gel P-100 column in the presence of SDS. It was found that the eluted substance containing trinitrophenyl group was composed from 47 Kd peptide.
On the basis of these observations, it was suggested that squid S1 heavy chain was made up of three peptides of 27, 47, and 23 Kd, arranging in the order from N-terminal to C-terminal end. It was also suggested that actin, regulatory light chain, and trinitrophenyl group binding sites were located on the link of 47 and 23 Kd peptides, on 23 Kd, and on 47 Kd peptide, respectively.
