Animal influenza virus neuraminidase: studies on dependence of some of its properties on its association with hemagglutinin.

Neuraminidase (Nase) thermostability and sensitivity to pH treatment as well as specific enzymatic activity (Nase activity per 1 HA unit) were determined in two groups of animal influenza virus strains containing equine 1 and equine 2 Nase subtypes, respectively (A/equine/Prague/56 (Heq1 Neq1), A/equine/Cambridge/63 (Heq1 Neq1), A/FPV/Dutch/34 (Hav1 Neq1), A/chicken/Germany "N" (Hav2 Neq1), in one group, and A/equine/Miami/1/63 (Heq2 Neq2), A/turkey/Canada/63 (Hav6 Neq2), A/duck/Ukraine/1/63 (Hav7 Neq2), in the other group). Nase of all the strains used was thermotabile when heated at pH 4.5. Nase of Neq1 subtype irrespective of strain containing it was thermolabilt when heated both at pH 6.5 and 8.1 and sensitive to pH 4.5 treatment as such (without heating). Inversely, Nase of Neq2 antigenic subtype irrespective of the strain containing it, was thermostable when heated at pH 6.5 AND 8.1 and resistant to the treatment of pH 4.5. Specific enzymatic activity was considerably higher in all the strains containing Neq2 as compared to Neq1-containing strains (4-6 times as much). The results suggest that thermostability and pH sensitivity of equine Nases of both antigenic subtypes, as well as their specific activities, do not depend on the sort of HA which is coupled with enzyme subunits at viral envelope, but attributed rather to properties of the subunits themselves, such as glycoprotein entities. The data concerning specific activities may suggest that in the case of various combinations of Nase subunits with different HA subunits the amount of enzyme per virion is of the same order.