Isolation of enzymatically derived fragments of guinea pig IgG and an examination of their reactivity against Staphylococcal protein A.

Papain digest of guinea pig IgG2 was separated by ion-exchange chromatography into five fractions, one containing mainly Fab and four Fc fractions. Covalently linked Fc (cFc) and non-covalently linked Fc fragments (nFc) were present, both with a molecular weight (Mw) of about 56,000. nFc was split into half fragments by gel filtration under dissociating condition (Mw 25,000 to 27,000). An incomplete Fc fragment (iFc) was also isolated (Mw 36,000), which consisted of a Fc chain (Mw 26,000) non-covalently linked to a piece of another chain. These preparations all reacted with protein A. In addition, the Fc' fragment (Mw 22,000), which is the C-terminus of the Fc fragment, was isolated. This fragment did not react with protein A. The cFc was treated with acid and then digested with trypsin at pH 7.8 for 45 s. The digest were separated into four fractions (I-IV) by gel filtration on Sephadex G-100. Fraction I was indistinguishable from intact Fc, fraction II contained an incomplete covalent Fc fragment (Mw 34,000 to 38,000). Both these fragments reacted with protein A. Fraction IV consisted of fragments belonging to the C-terminus, and was protein A non-reactive. Fraction III was shown to contain a mixture of fragments belonging to fractions II and IV.