Fab production, purification and sequencing. A. Chromatogram of separation of papain digestion products using Superdex-75. The undigested mAb (I) is eluted first, followed by the Fab fragments (II & III) and the Fc fragments along with other small digestion products (IV) are collected last. Bottom right: Analysis of fractions 1–5 on 10% SDS gel demonstrate separation of the Fab fragments (47 kDa) from the over-digested Fab fragments (≈ 37 kDa). Top right: Schematic diagram of mAb digestion by papain as previously described in literature . The bold arrow indicates were papain digests primarily before the cysteine-bridges on mAb (I). The papain can also digest the Fab fragment produced (II), as indicated by dashed arrow. The digested Fab (III) may be missing one of the Fv regions. B. The variable regions of 7C8 and 3C4 heavy and light chains, are aligned respectively. The CDR regions as indicated by immunoglobulin superfamily database http://imgt.cines.fr are shaded.