Ovalbumin (Molecular Biology)

The major protein in egg-white is ovalbumin. It has the typical highly ordered structure of a serpin (see Fig. 1 in that entry), but has lost the ability to refold the loop that would correspond to its reactive center; consequently it has no proteinase inhibitor activity. Its smallness relative to other serpins, and its conformational stability, make it suitable as a marker for gel electrophoresis. The stability is only relative, however; its reactive-center loop can be cleaved proteolytically to produce a form known as plakalbumin. It is likely that the induced insertion of this loop, like that that occurs in other serpins, explains a conformation, with increased stability, that forms on long-term storage: S-ovalbumin.