An Active Antibody Fragment (Fv) Composed of the Variable Portions of Heavy and Light Chains

An active antibody fragment of molecular weight 25,000 was prepared in high yield by pepsin digestion of protein 315, a mouse IgA myeloma protein possessing anti-2,4-dinitrophenyl activity. This fragment, denoted Fv, is the N-terminal half of the Fab fragment and is composed of two peptide chains held together by noncovalent bonds. These peptide chains were separated by chromatography on DEAE-cellulose in 8 M urea. The molecular weight of each of the chains in 5.7 M guanidine hydrochloride was found to be 12,500. The separated chains were identified by N-terminal analysis and partial sequence and amino acid composition as the variable portions of the light and heavy chains (V_L and V_H) and they contain 110-120 residues each. Amino acid composition also suggests that the position of the pepsin split in the L chain is around residue 115. The separated, inactive V_L and V_H can readily recombine, upon mixing in an equimolar ratio, to yield an active fragment.