The effects of cleavage of the inter-chain disulphide bonds of rabbit IgG on its ability to bind C1q

Abstract

Immune complexes prepared from rabbit anti-ovalbumin IgG in which the interchain disulphide bonds had been reduced and then blocked with N-(iodoacetylaminoethyl)-8-naphthylamine-1-sulphonic acid retained the ability to bind 125I-labelled C1q. This ability was lost when a small alkylating agent (iodoacetamide) was used to block the cleaved disulphide bonds. The ability of the IgG to form insoluble immune complexes was partially compromised when iodoacetamide was used to block the disulphide bonds, but was unimpaired when N-(iodoacetylaminoethyl)-8-naphthylamine-1-sulphonic acid was used. These data are consistent with the suggestion that access to the C1q binding site in IgG in immune complexes is modulated by movement of the Fab arms, which may block access to the site.