The presence of two neuraminidases in an influenza virus

Abstract

The wild type influenza strain A/Aichi/2/68 (H3N2), when disrupted with SDS and electrophoresed on cellulose acetate paper, yielded two separate neuraminidases, NA(H+) and NA(H-). These enzymes after extraction were biologically active and possessed different specific activities. Enzyme NA(H+) possessed neuraminidase as well as hemagglutinin activities whereas enzyme NA(H-) demonstrated only neuraminidase activity. Similar results were obtained when the Aichi strain was treated with Tween-ether and the two enzymes were separated by affinity chromatography. Techniques used failed to separate the hemagglutinin activity from neuraminidase NA(H+). These results suggest that the dual activity present in enzyme NA(H+) may be characteristic of this protein. Both enzymes are antigenically different and are apparently present as distinct entities in the Aichi strain. Experiments showed that only enzyme NA(H-) of the Aichi strain was incorporated into the hybrid X-32 virus during genetic recombination.

In vitro enhancement of human natural cell-mediated cytotoxicity by purified influenza virus glycoproteins

“…The suspension was centrifuged, and the supernatant was layered on a preformed sucrose density gradient (5 to 20%). Fractions containing the HA and NA activities were collected, and these proteins were further purified by affinity chromatography with appropriate adsorbents as already described (2). IFN.…”

“…Determination of HA activity. Samples were serially diluted twofold with phosphate buffered saline (0.01 M sodium phosphate buffer [pH 7.2] containing 0.85% NaCl) and added to a washed chicken erythrocyte suspension (0.5%) as already described (2).…”

“…Determination of NA activity. The NA activity was measured by incubating samples at 37°C with fetuin (25 mg/ml) for 18 h. Liberated N-acetylneuraminic acid was determined by absorbance at 549 nm (2).…”

“…Rabbits were bled 12 days after the last injection. The specificity of the antisera was evaluated by double immunodiffusion and inhibition tests (2). It is important to point out that the monospecific anti-HA antiserum neither neutralized the NA activity nor gave a precipitin line by double immunodiffusion test against NA, whereas the antiserum produced by injection of purified viral HA neutralized its HA activity, gave precipitin lines when double immunodiffusion tests were performed, and did not cross-react against viral NA.…”