Isolation of an active heavy-chain variable domain from a homogeneous rabbit antibody by cathepsin B digestion of the aminoethylated heavy chain.

Cathepsin B from bovine liver has been used to cleave the heavy chain of partially reduced and aminoethylated rabbit allotype a1 IgG. Three major cleavages have been identified, one of which appears to be at the peptide bond carboxy terminal to the two adjacent (aminoethyl)cysteine residues at positions 133 and 134. The variable domain of the heavy chain (VH) was isolated by gel filtration from both pooled heterogeneous rabbit IgG and a homogenous rabbit antitype III pneumococcal polysaccharide antibody. This VH inhibited the binding of 125I-labeled (allotype a) IgG to anti-a1 allotypic antibodies. The recombinant molecule consisting of VH and light chain from the homogeneous antibody is active in an antigen binding assay.