4-Methylumbelliferyl-α-Glycosides of Partially0-AcetylatedN-Acetylneuraminic Acids as Substrates of Bacterial and Viral Sialidases

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Abstract
4-O-Acetylated, 7-O-acetylated, and 9-O-acetylated 4-methylumbelliferyl-.alpha.-N-acetylneuraminic acids (Neu4,5Ac2-MU, Neu5,7Ac2-MU, Neu5,9Ac2-MU) were tested as substrates of sialidases of Vibrio cholerae and of Clostridium perfringens. Both sialidases were unable to hydrolyse Neu4,5Ac2-MU. This compound at 1mM concentration did not inhibit significantly the cleavage of Neu5Ac-MU, the best substrate tested. The 4-O-acetylated sialic acid glycoside is hydrolysed slowly by the sialidase from fowl plague virus. The relative substrate specificity, reflected in V/Km of the V. cholerae sialidase is Neu5Ac-MU .mchgt. Neu5,7Ac2-MU .apprxeq. Neu5,9Ac2-MU and of the clostridial enzyme it is Neu5Ac-MU > Neu5,9Ac2-MU > Neu5,7Ac2-MU. The affinities of both enzymes for the side-chain O-acetylated sialic acid derivatives are higher than for Neu5Ac-MU. The artificial, well-defined substrates, described here, provide the opportunity to quantify the influence of sialic acid O-acetylation on the hydrolysis of sialoglycoconjugates without the side effects introduced by other parts of more complex glycans.