Monoclonal-antibody studies of creatine kinase. The proteinase K-cleavage site

Abstract

Proteinase K cleaves a small peptide from native muscle-specific creatine kinase. Studies of the binding of 2 monoclonal antibodies to formic acid-cleavage fragments and proteinase K-digest fragments of chick muscle creatine kinase suggest that the proteinase K-cleavage site is in the C-terminal region of the molecule. This specificity of proteinase K, which is not normally a highly specific enzyme, and the continued association of the 2 peptide fragments after cleavage suggest an unusual conformational feature in the cleavage-site region. By applying predictive methods for hydrophobicity and secondary structure to an amino acid sequence in this region, possible structural features at the cleavage site that are evidently conserved across avian and mammalian species are proposed. The most likely site is next to, or within, a .beta.-turn on the surface of the molecule.