[Fragmentation of myosin A-1 light chain of fast muscle by trypsin]

Limited proteolysis of myosin by such proteolytic enzymes as trypsin, chymotrypsin or papain produces typical fragmentation of its heavy chain. Presently evidence is given that trypsin treatment cleaves the alkali light chain A-1 (20,700 dalton) to a shorter (ca 20,000 dalton) chain. The two "essential" thiols (SH-1 and 2) of moysin were alkylated with 17-C-N-ethylmaleimide and a non-negligible amount of radioactivity was also found in the two alkali light chains. Using the specific radioactivity of alkali light chain A-1 it was possible to identify it among heavy chain fragmentation products. The molecular weight of the newly formed A-1 indicates that limited tryptic cleavage of this A-1 confers on it a closer similarity with alkali light chain A-2.