The polypeptides of influenza virus: VI. Composition of the neuraminidase

The neuraminidase of influenza B/Lee is a polymer composed of 4 molecules of glycoprotein of M r 63,000. Disulfide bonds link the monomers into pairs which in turn aggregate by noncovalent bonds. A second protein of M r 56,000 is found in smaller amounts in some preparations. Neuraminidase released from the virion by trypsin treatment differs from that released by sodium dodecyl sulfate (SDS) in that it cannot aggregate, migrates somewhat differently in electrophoresis, has a slightly lower molecular weight, and contains relatively less glucosamine. On electrophoretic analysis the monomer from the trypsin-derived enzyme is found to be exclusively of 56,000 M r. The evidence suggests that it is derived from the “natural” glycoprotein by the loss of a carbohydrate-rich fragment from the hydrophobic (envelope-associated) region of the molecule.