Amidase and peptidase activities of polyclonal immunoglobulin G present inthe sera of patients with rheumatoid arthritis

Polyclonal Immunoglobulin (Ig) G from patients with rheumatoid arthritis (R A) and healthy subjects hydrolyzed carbobenzoxy-val-Gly-Arg p-nitroanilide and D-Pro-Phe-Arg p-nitroanilide. RA IgG exhibited higher activity against the former substrate, but not the latter. On the other hand, RA IgG showed reduced activity against D-Pro-Phe-Arg methylcoumarinamide, when compared w ith those of the healthy controls. These results suggest that RA IgGs diffe r from normal IgGs in the substrate specificity of amidase activity. Prelim inary studies have shown that two out of three RA IgG samples cleaved a pen tapeptide-Gln-Arg-Arg-Ala-Ala-which is assumed to be associated with the ri sk of developing RA (Gregersen, P. K. et al. (1987), Arthritis Rheum. 30, 1 205-1213). By contrast, virtually no cleavage of the same peptide was obser ved with IgG from healthy controls. A peptide analog, Gln-Arg-Arg-Trp-Ala, was not cleaved at all by any IgGs examined either from RA patients or heal thy controls.