Cell adhesion molecules were originally identified using antibodies raised against cell-surface components to block cell aggregation. In the adhesion-blocking assays, the researchers found it necessary to use antibody fragments, each with a single binding site (so-called Fab fragments), rather than intact IgG antibodies, which are Y shaped molecules with two identical binding sites. The Fab fragments were generated by digesting the IgG antibodies with papain, a protease, to separate the two binding sites (Figure Q19–1). Why do you suppose it was necessary to use Fab fragments to block cell aggregation?

Figure Q19-1

Transcribed Image Text:

sites of раpain cleavage sites for antigen binding PAPAIN IgG antibody Fab fragments