Chemical Modification of Human and Rabbit Antistaphylococcal γG Antibodies: Effect of Acetylation, Carbamylation and Amidination on Opsonic Activity

Abstract

Abstract Opsonically active γG-globulins isolated from five patients with staphylococcal subacute bacterial endocarditis and two hyperimmunized rabbits were subjected to acetylation, carbamylation and amidination to determine if substitution of chemical groups in the γG molecule would result in loss of opsonic activity. The degree of chemical substitution was monitored by the ninhydrin reaction. In vitro opsonic capacity of all γG preparations tested decreased with progressive acetylation or carbamylation. No preparations were opsonically active after substitution of 50% of the free amino groups. The ability of the antibodies to react with staphylococcal antigens was not significantly diminished by these treatments. Both acetylation and carbamylation produced a marked increase in the net negative charge of γG globulin and significantly altered antigenic determinants of both light and heavy chains. Limited alteration of γG opsonins was obtained with ethylacetimidate which substitutes only at α and ε amino groups. Amidination of up to 87% of the free amino groups did not alter the charge of the γG preparations and resulted in only minor changes in antigenic determinants of the light and heavy chains. The ability of the antibody to combine with staphylococcal antigens was retained. The opsonic capacity of human γG was abolished by substitution of 65% of the free amino groups. A comparable degree of amidination of rabbit γG globulin had no significant effect on its opsonic activity.