© 2006 The Japanese Biochemical Society.
Regular Paper |
Variation in the Divalent Cation Requirements of Influenza A Virus N1 Neuraminidases
Department of Pediatrics, Division of Critical Care Medicine, Weill Medical College of Cornell University, 525 East 68th St., New York, NY 10021, USA
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Enzymatic kinetic parameters of influenza A virus N1 neuraminidases (NA) chromatographically purified from several vaccine candidate strains were tested. With ionic strength held constant, Ca2+ or Mg2+ increased the initial rate of enzymatic activity. The 1934 and 1943 strains had statistically significant highest initial velocities, Vmax/Km and Vmax. There were no significant differences among the influenza virus strains from 1947 to 1991. Measured Km for the 1943 strain (6.2 x 10–5 M) was significantly higher than other strains (3.1–4.7 x 10–5 M). Vmax/Km varied from 0.78 M–1 s–1 to 0.91 M–1 s–1 and Vmax varied from 3.0 s–1 to 5.5 s–1 before the addition of a divalent cation and increased approximately 2-fold for each of these kinetic parameters for each strain after the addition of exogenous Ca2+ or Mg2+. Dialysis reduced the initial velocity and immunogenicity of each strain with significant differences found among strains. Enzymatic activity and immunogenicity were partially restored by the addition of exogenous Ca2+. Nucleic acid sequence analysis could not predict these differences. Selection of vaccine strains must include analysis of antigenic changes, but also enzymatic studies and determination of the requirement of divalent cations to maintain immunogenicity and activity during production.