Major proteins of beer and their precursors in barley : electrophoretic and immunological studies

SDS-PAGE analysis revealed that what was considered the major protein of beer is actually formed by two polypeptides with the same molecular mass (∼40 kDa), but different hydrodynamic volumes in their incompletely unfolded conformation. The two polypeptides share common properties, although the one with the more open conformation is associated with sugars, whereas the other is not. Immunoblotting experiments with polyclonal antibodies raised against the two electrophoretically purified polypeptides indicated that they are immunologically related and allowed the identification of their precursors in barley grain. These latter are two heat-resistant albumins whose electrophoretic behavior corresponded to that of beer proteins. These two albumins coincide with protein Z, the first member of the serpin superfamily described in plants.