Studies on Fd-fragments of human immunoglobulins: II. The preparation and characterization of peptic (Fab′) 2-fragments and an Fd′-fragment of IgA-myeloma proteins

Abstract

Pepsin digestion of unfolded human 7 S IgA1 myeloma proteins and of an unfolded IgA2 (1+) protein produced, under certain conditions, fragments which are similar with respect to gel filtration. The fragments contained light chains and part of the α-chains as judged by immunodiffusion experiments and urea starch gel electrophoresis. From approximate molecular weight determinations by thin layer gel filtration together with characterization of the fragments by ultracentrifuge experiments, it was concluded that (Fab′) 2-like fragments had been prepared. The nature of the fragments is discussed in relation to the observed antigenic heterogeneity of (Fab′) 2-like fragments from distinct myeloma proteins. Finally an Fd′ α-like fragment could be isolated from one of the studied myeloma proteins; the relevance of this result is discussed in the light of the structure of Fab from human immunoglobulins.