Properties of delipidated hepatitis B surface antigen (HBsAg) and preparation of its proteolytic cleavage fragments carrying HBsAg-specific antigenic determinants.

Treatment of hepatitis B surface antigen (HBsAg) with either chloroform-methanol (2:1, v/v) or 50% 1,1',3,3'-tetramethylurea did not affect the morphological integrity of the particles (about 20 nm in diameter), although the major portion of lipids was released as indicated by their increased buoyant density in CsCl (1.27 g/cm3 as compared with 1.20 g/cm3 for intact HBsAg). The antigenicity and polypeptide composition of HBsAg was not altered by delipidation. The carbohydrate chains of HBsAg contain penultimate beta-D-galactosyl residues. HBsAg was cleaved by chymotrypsin into fragments which were smaller than intact HBsAg by two orders of magnitude and which contained both the a and d determinants.