An Electron Microscopic Study of the Structural Polymorphism of Hepatitis B Antigen

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Abstract
Particulate hepatitis B antigen (HB Ag), purified by several different methods, was suspended in buffers of various ionic strengths and pH and digested with peptidases, nucleases, and organic denaturing reagents. In water and dilute buffer two forms of HB Ag predominated: tubes with cross-striations of 3-nm periodicity and small, solid round particles. The modal diameter of the small particles differed with the method of purification and the buffer. Ring forms of the round particles were very prominent in 0.125 M phosphate buffer and in 4 M urea. In phosphate buffer the tubes lost their cross-striations and seemed to uncoil. Large (40–80 nm) multistranded forms, with up to four lamellar-type strands, appeared in 0.125 M phosphate buffer and when HB Ag was digested with 0.1% chymotrypsin. At acid pH tube forms disappeared and left mainly small round particles. It is proposed that the observed structural polymorphism of HB Ag was dependent on protein-protein interactions. The small round particles may be disks of tightly wound helical protein that can stack to form tubes of various lengths.

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