A polypeptide containing 55 amino acid residues coded by the pre-S region of hepatitis B virus deoxyribonucleic acid bears the receptor for polymerized human as well as chimpanzee albumins.

The receptor for polymerized human and chimpanzee albumins has been identified on a hepatitis B surface antigen polypeptide of approximately 31,000 daltons. The polypeptide, designated P31, is composed of the major polypeptide of hepatitis B surface antigen (P22) and an additional, as yet unidentified, amino acid sequence. We split P31 with cyanogen bromide and obtained a polypeptide of approximately 8000 daltons (P8) that contained carbohydrate. P8 could bind to polymerized human and chimpanzee albumins, but not to polymerized albumins from animals without susceptibility to hepatitis B virus. The amino acid composition of P8 closely resembled that of 55 amino-acid sequence coded by the pre-S region in the deoxyribonucleic acid of hepatitis B virus. Using monoclonal antibody against P8, a solid-phase sandwich radioimmunoassay was developed for the specific determination of hepatitis B surface antigen bearing the receptor for polymerized albumin in the serum of patients with hepatitis B virus infection.