Sialidases aglycone

More insight into the subcellular distribution of sialidases in intact cells is possible by histochemical means. For this purpose, 2-(5-bro-moindol-3-yl)-a-Neu5Ac and 2-(6-bromo-2-naphthyl)-a-Neu5Ac were synthesized, and the enzymieally liberated 5-bromoindole or 6-bromo-2-naphthol aglycon was spontaneously oxidized,189 or coupled to... 

A particular problem is the demonstration of inversion with sialidases, since they act on ot-A-acetylneuraminides, but the mutarotational equilibrium is 10% ot 90% The chemical shifts of the two H3 protons have different chemical shifts in the ot- and p-forms of A-acetylneuraminic acid and its mutarotation is not inconveniently fast, so demonstrating retention is straightforward. However, to demonstrate inversion, it is necessary to match the rate of liberation of aglycone with that of a retaining sialidase and plot time courses for both enzymes, in order to distinguish inversion from uninformative conversion of substrate to the equilibrium mixture i.e. it has to be demonstrated that the chemical flux through the system is easily adequate to maintain non-equilibrium proportions of a- and p-A-acetylneuraminic acid. 

M. (1995) Effect of substrate aglycon on enzyme mechanism in the reaction of sialidase from influenza virus. FEBS Letters, 372, 148-150. 

To date, various assay methods for sialidase activity have been developed. In principle, the hydrolytic reaction catalyzed by sialidase can be assayed by quantitating the released sialic acid or aglycone. The thiobarbituric acid procedure described by Warren (1959) or its modification by Aminoff (1961) is used frequently for the colorimetric determination of released, free sialic acid. 

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