Similarity of Peptides in Two Antigen-combining Fragments released from a Rabbit Antibody by Papain

Abstract

DURING an examination of the enzymatic hydrolysis of rabbit γ-globulin, it was noted that only one-half to two-thirds as many peptides could be differentiated in the hydrolysates as was expected from the amount of base needed to maintain pH during hydrolysis : approximately 50 peptides were distinguished following hydrolysis of rabbit antibodies with trypsin, 70 following chymotrypsin and 100 following subtilisin, whereas approximately 100, 150 and 210 µmoles of sodium hydroxide per µmole of antibody respectively were required to maintain pH at 8.0. The results suggested the possibility that similar or identical peptides were released from different parts of the same molecule resulting in a smaller number of detectably different peptides than the number of peptide bonds broken. An opportunity to test this hypothesis was afforded by Porter's isolation of three large peptide fragments from papain hydrolysates of rabbit γ-globulin¹. Two of these, I and II, had antibody characteristics and together comprised 50–60 per cent of the antibody molecule; the third fraction, III, was easily crystallized but had no antibody activity. In the work reported here, the peptides of these three fragments were compared.