PROTEOLYTIC FRAGMENTATION OF MYOSIN - LOCATION OF SH-1 AND SH-2 THIOLS

The H chain fragmentation pattern of native myosin when digested by proteolytic enzymes is influenced by such conditions as the nature of the proteolytic agent, ionic strength and presence or absence of divalent cations. HMM and S-1 produced by digestion of 14C-NEM[N-ethylmaleimide]-labeled myosin under various conditions were analyzed by sodium dodecyl-sulfate polyacrylamide gel electrophoresis. Purified samples of these species were digested under controlled conditions by chymotrypsin and trypsin, and a comparison of the observed H chain fragmentation patterns led to a sequential arrangement of the proteolytic fragments. The main features of this arrangement are described. A 21 K [kilodaltons] MW tryptic peptide is found at the N-terminal side of myosin H chain. Adjacent to it is a 48 K peptide, then a 19.5 K peptide containing the two SH-1 and SH-2 thiols. These 3 peptides constitute the H chain of S-1. Adjacent to this S-1 H chain is a tryptic (and also chymotryptic) 40 K peptide. The rest of the HMM H chain on the C-terminus is a sequence susceptible to both chymotrypsin and trypsin attack yielding an undefined number of small peptides.