Immunochemistry and Polypeptide Composition of Hepatitis B Core Antigen (HBc Ag)

Abstract

Core particles were isolated from a nuclear extract of a hepatitis B-infected liver, labeled with ¹²⁵I by using chloramine-T and further purified by rate zonal sedimentation on sucrose gradients. Iodinated HB_c Ag was used as a ligand in a sensitive double-antibody radioimmunoprecipitation (RIP) assay for antibody to HB_c Ag. The specificity of the RIP reaction was evaluated using defined anti-HB_c sera and paired sera from six well-documented cases of hepatitis B infection. The polypeptide composition of the iodinated antigen was examined by SDS-polyacrylamide gel electrophoresis of solubilized complexes of ¹²⁵I-HB_c Ag and anti-HB_c. Two major polypeptides with apparent m.w. of 17,000 and 35,000 daltons were observed and designated as cP-1 and cP-2, respectively.