Ultrastructure and some biological properties of influenza A virus. I. Alterations in the activity of surface antigens of influenza A virus by enzymes and infectious activity of such changed viruses.

Strain of A/ZSRR/053/74 (H3N2) virus was subjected to the action of enzymes. Treatment of the virus with soluble trypsin and trypsin bound to a carrier for different periods of time resulted in decreased neuraminidase activity and infectivity, however, hemagglutinin activity was preserved. After treatment pickled with soluble bromelain, virions of decreased hemagglutinin amount but preserved neuraminidase activity, were obtained. This was accompanied by a slight fall in the infectivity. Bromeline bound to a carrier produced different results. It exerted a destructive effect on neuraminidase activity, decreasing virus infectivity and only slightly hemagglutinin titer. Chromatographically purified fractions of virus with very low hemagglutinin titer and undeterminable neuraminidase, did not completely loose their infectivity.