The effect of chemical modification of amino groups of rabbit γ G antibody on its PCA activity in guinea pig and rabbit skin was studied, with particular attention to high degrees of carbamylation which have profound effects on the antibody's ability to fix complement and to aggregate with antigen. It was concluded that there is no evidence at present for the selective inactivation of specific PCA sites on the Fc portion of the antibody molecule by these reagents. Rather, the observed loss of PCA reactivity in rabbit skin could be attributed to the impaired ability of the antibody to fix complement. Loss of PCA activity in guinea pig skin required greater than 90% carbamylation of the antibody molecule and could be explained in terms of the nonspecific effects on the molecule produced by such treatment. It was further observed that the loss in PCA activity under these conditions could be potentiated in a system in which cross-reacting antigen was used.

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