Circular dichroism and biochemical properties of the hepatitis B virus core antigen

The hepatitis B virus (HBV) core antigen was purified by mild procedures, including hydroxyapatite column chromatography, with care taken to avoid the degradation of the particles. Circular dichroism (CD) of the HBV core particles in saline showed low intensities of negative ellipticities in the region dominated by amide bond absorption. Acid treatment of the particles induced a remarkable change in the CD spectrum, with the appearance of a positive extremum at about 208 nm. The amino acid composition and the COOH-terminal residue of the isolated core polypeptide (Mr 21,000-21,500) were shown to be essentially the same as those of the polypeptide deduced from the nucleotide sequences which had been proposed for the HBV core antigen by other laboratories. We failed to detect any NH2-terminal dansyl-derivatives from the core polypeptide by the dansyl-Edman method. We also showed by the method of fluorescein polarization that the core polypeptide conjugated with fluorescein isothiocyanate has an affinity for serum albumin. This may indicate a state of disassembled or non-assembled core polypeptide in sera.