EPITOPE OF 24G7 ANTI-BILIRUBIN MONOCLONAL-ANTIBODY

We examined an antigenic epitope recognized by an anti-bilirubin monoc lonal antibody designated 24G7 (Shimizu, S., Izumi, Y., Yamazaki, M., Shimizu, K., Yamaguchi, T., and Nakajima, H. (1988) Biochim. Biophys. Acta 967, 255-260). The reactivity of bilirubin-IX alpha, its analogue s (III alpha, XIII alpha and mesobilirubin-IX alpha) and related azo c ompounds, with 24G7 was compared by means of an enzyme-linked immunoso rbent assay (ELISA). The order of reactivity was as follows: (a) anili ne azopigment > ethyl anthranilate azopigment > sulfanilic acid azopig ment, (b) bilirubin-XIII alpha > bilirubin-IX alpha > bilirubin-III al pha, (c) bilirubin-IX alpha = mesobilirubin-IX alpha. These findings i ndicated that the epitope is present in (a) the dipyrrolic moiety of t he endovinyl (correspond to N-21 and N-22 of bilirubin), or exovinyl t ypes (N-23 and N-24); (b) the dipyrrolic moiety of the endovinyl type, which contains (c) a methyl group (C-2) but not a vinyl group (C-3) i n the dipyrrolic moiety of endovinyl type. Therefore, we concluded tha t the epitope was the region containing the oxo group at C-l, the meth yl group at C-2, C-(4,5,6,9), and the N-21 and -22 of bilirubin-IX alp ha.