Studies on glycoproteins X. Equilibrium measurements on influenza virus-glycoproteins systems

Measurements in systems of enzymically inactive influenza viruses and sialoglycoproteins disclosed an equilibrium between the free reactants and the virus-glycoprotein complex. Equilibrium constants were determined by two methods: equilibrium filtration and ultracentrifugal separation. The glycoproteins tested were influenza virus haemagglutinin inhibitors of high potency (ovine submaxially glycoprotein) and low potency (fetuin, orosomucoid and trypsin-treated OSM). The equilibrium constants (in molar terms) were found to be 1·10⁻⁸ for OSM, 9·10⁻⁷ for fetuin, 2·10⁻⁵ for orosomucoid and 4·10⁻⁶ for the glycopeptides (assumed mol. wt. 50000) obtained by controlled trypsin treatment of OSM. Weight for weight OSM was 17 times more firmly bound to enzymically inactive Lee virus than were its constituent glycopeptides as formed on trypsin treatment.

The number of negatively charged terminal sialic acid residues attached simultaneously to complementary groupings at the virus surface, appears to determine primarily the inhibitory potency of the glycoproteins. This determinant is a compound of the number of sialic acid residues available per glycoprotein molecule and of the complementariness of the contacting areas on the surface of virus and glycoprotein.