| Popis: |
Neuraminidase activity of virulent and vaccinal strains A/England/42/72, A/Scotland/840/74 and A/Victoria/3/75 assessed at different temperatures did not show significant differences in the temperature optima of enzyme activity. Vaccinal strains were attenuated by APR-8 recombination and selection of mutants resistant to serum inhibitors (Alice, RIT 4025, RIT 4050 strains). On the contrary, differences were found in the thermal inactivation of the neuraminidase between wild and vaccinal strains, the latter being more thermolabile. Increasing from 0.5 to 5.0 mM/1 the Ca++ concentration, an enhancement of the heat stability was observed, more marked for the attenuated strains. The amount of NANA released by 1 hemagglutinating unit varied widely between strains. To be pointed out, however, that within each antigenic variant the vaccinal strain showed a lower enzymatic activity than the corresponding wild strain. |
