Neuraminidase from influenza virus A (H3N2): specificity towards several substrates and procedure of activity determination

Neuraminidase (acylneuraminyl hydrolase, EC 3.2.1.18) from the influenza virus A/Hong Kong/68 (H3N2) was purified after treatment of the purified virus with sarcosyl (sodium laurylsarcosinate), centrifugation at 110 000 x g, and chromatography on DEAE-Sephadex and Sephadex G-200. It migrated as a single component during electrophoresis on polyacrylamide gel, and its molecular weight was estimated about 270 000. The enzyme was thermolabile, the activity being reduced to 60% in 10 min at 50 degrees C. The purified neuraminidase had an apparent Km value of 4.1 . 10(-3) M for 5-N-acetyl-2-O-(3-methoxyphenyl)-alpha-D-neuraminic acid and was able to release sialic acid with linkages alpha 2-3, alpha 2-6 and alpha 2-8 (with very different efficiency) from fetuin, gangliosides, colominic acid, and bovine and porcine submaxillary mucins. The enzymic activity was measured by several procedures: (A) spectrophotometric determination at 340 nm of the NADH produced in the reaction catalysed by beta-galactose dehydrogenase on beta-galactose + NAD+, this beta-galactose was the product released from lactose by beta-galactosidase and lactose was the product of the neuraminidase activity on N-acetylneuraminyl-lactose; (B) determination of the colored quinone yielded by the liberated methoxyphenol with 4-aminoantipyrine (Santer, U.V., Yee-Foon, J. and Glick, M.C. (1978) Biochim. Biophys. Acta 523, 435-442); (C) periodate-thiobarbiturate procedures (Warren, L. (1959) J. Biol. Chem 234, 1971-1975 or Aminoff, D. (1961) Biochem. J. 81, 384-391). Some peculiarities of these methods are discussed.