PEPSIN DIGESTION OF HUMAN G-MYELOMA PROTEINS OF DIFFERENT SUBCLASSES I. THE CHARACTERISTIC FEATURES OF PEPSIN CLEAVAGE AS A FUNCTION OF TIME.

The techniques of starch gel electrophoresis, immunoelectrophoresis and high resolution gel filtration have been used to investigate the peptic cleavage or human G-Myeloma proteins of the four known subclasses. The appearance and fate of F(ab')2 and pFc' fragments and the persistence of undegraded IgG have been contrasted and distinctive patterns of pepsin sensitivity have been established for each subclass. The IgG 1 subclass is the most resistant and is degraded by pepsin in a manner which is closely similar to that observed for pooled IgG. IgG 2 molecules are also relatively resistant to peptic cleavage whereas IgG 3 and IgG 4 proteins are much more sensitive. Nevertheless all the subclasses are cleaved by the enzyme in similar susceptible regions and give rise at some stage to the same products: F(ab')2 fragment, pFc' fragment and peptides from the N-terminal half of the Fc region. [ABSTRACT FROM AUTHOR]