Characterization of 'e' antigen associated with hepatitis B

Hepatitis B 'e' antigen (HBe) from the serum of a chronic carrier of HBsAg has been partially purified and characterized. It behaves as an acidic protein, pI 4.5--5.0, which is thermolabile and sulphydryl-sensitive. In serum it usually has a flotation density 1.3 g/cm3, but is sometimes found at density 1.15 g/cm3 because of its association with lipid. HBe from serum is polydisperse on gel filtration although most antigen is recovered with a nominal molecular weight of 3 x 10(5) Daltons. In contrast, in the presence of chaotropic ions, the bulk of serum HBe is found as a species of 3 X 10(4) Daltons previously detected in small amounts under non-dissociating conditions. This suggests that the larger material is formed by non-covalent association of the 3 X 10(4) Dalton species either with itself or other serum components. This would include IgG, although there is no evidence that HBe itself bears immunoglobulin determinants. Analysis of HBe precipitins by polyacrylamide gel electrophoresis under reducing and dissociating conditions suggests that its component polypeptide chains are about 1.7 X 10(4) Daltons.