Specific cleavage of immunoglobulin G by copper ions

The hinge region of a recombinant‐DNA‐produced human IgG1 (Campath 1H) is specifically cleavable at a single copper‐sensitive peptide bond, yielding a distinct fragment resolved by size‐exclusion high‐performance liquid chromatography. This novel metal ion‐catalysed cleavage at slightly alkaline pH is inhibited by EDTA and its rate is reduced at slightly acidic conditions (pH5‐6) and accelerated by increasing concentrations of cupric ion and higher temperature. Complete cleavage was observed after incubation at pH 8 for 24 h with 1 mM CuC12. Sequence analysis determined the cleavage site to be the Lys226‐Thr227 bond in the hinge‐region sequence DKTHT. Cleavage of other IgGs was observed to varying degrees, and specific cleavage of synthetic peptides containing this pentapeptide sequence was also observed. © Munksgaard 1996.