Cleavage sites of human IgGl immunoglobulin by papain

Abstract Papain digestion of human IgGl myeloma proteins was investigated. Under the conditions used in our experiments, papain cleaves a majority of the IgGl molecules in a stepwise fashion. It first splits a histidine-threonine bond between positions 224 and 225 of the heavy chain, and subsequently, a glutamic acid-leucine bond between positions 233 and 234 of the heavy chain. The first cleavage site is located in the hinge region at the amino-terminal side of the inter-heavy-chain disulfide bridges, whereas the second cleavage site is 9 amino acid residues apart from the first site at the carboxyl-terminal side of these bridges. Further cleavage by papain led to degdradation of the Fc fragment into many small peptides.