Denaturation studies, amino and carboxyl group modifications of the major ragweed pollen allergen antigen E were carried out. The studies show that antigen E consists of two polypeptide chains. These two chains with mol. wt of 21,800 and 15,700 are held together in the native antigen by non-covalent forces, and they can be dissociated in the presence of urea, guanidine hydrochloride or sodium dodecylsulfate. The urea denatured antigen E was about 104-fold less allergenic than the native antigen by direct skin tests on patients. It was a poor immunogen in rabbits, and the anti-sera produced cross reacted weakly with the native antigen. The chemical reactivities of the amino and the carboxyl groups of antigen E on modification suggested that they both can be divided into two classes, the accessible and the inaccessible class. Modification of the accessible amino or carboxyl groups of antigen E did not change markedly its allergenic activity or its reaction with sheep anti-antigen E sera. Modification of both classes of amino or carboxyl groups of antigen E invariably gave aggregated derivatives which showed greatly diminished allergenic activity and lost its capacity to combine with sheep anti-antigen E sera.
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