Isolation of the C-terminal peptides of rabbit skeletal myosin

Purified LMM and its tryptic fragments (LF-1, LF-2 and LF-3) were treated with carboxypeptidase-A and the liberated amino acids were identified by thin layer ion-exchange charomatography. In each protein the only detectable amino acid was leucine. From the total tryptic digest of LMM the C-terminal leucine containing peptides were isolated. Two peptides were found with the following amino acid composition: asx1, g1x6, ala1, leu3, and g1n2-3, leu1, respectively. We obtained the same two peptides from the total tryptic digest of LF-3. We conclude that the C-terminal amino acid of the myosin heavy chain is leucine rather than isoleucine as suggested earlier. Heterogeneity of isolated C-terminal peptides might indicate a heterogeneity in the myosin heavy chains.