Differential effect of guanidine hydrochloride and heat on the haemagglutinin and neuraminidase of influenza viruses

Summary

The effect of guanidine or heat on the haemagglutinin and neuraminidase of thirty strains of influenza virus showed a considerable variation among the strains in the sensitivity of the two surface glycoprotein subunits of the virus to these agents. The kinetics of inactivation was complex, and could not be expressed in terms of a simple mathematical exponential function. However, correlation diagrams plotted with the logarithm of the residual haemagglutinin or neuraminidase activity at a selected point (30 minutes) in the inactivation process showed a general pattern of grouping, which in the case of the haemagglutinin did not completely reflect the conventional serological classification of the strains. The neuraminidase correlation diagram on the other hand evidently reflected the antigenic grouping of the strains into subtypes, N1 and N2, and also differences were detected in the behaviour of strains showing antigenic “drift” within a subtype. Because guanidine attacks the relatively weaker polar linkages especially hydrogen bonding, its differing effects on the surface glycoproteins of different strains reflect alterations in the molecular configuration of the enzyme molecule. Such changes are also probably associated with antigenic changes such as from one subtype to another (“shift”) or in antigenic “drift”.