The action of sialidases on substrates containing O-acetylsialic acids.
O-Acetyl substitution of sialic acids in glycoconjugates reduces the rate of action of sialidases on these substrates. A plasma glycoprotein fraction and an erythrocyte ganglioside containing 4-O-acetylsialic acids were isolated and characterized from equine blood, and a sialyllactose preparation with Neu5,9Ac2 was purified from rat urine. Using the novel substrates II3Neu4Ac5Gc-LacCer and II3Neu5,9Ac2-Lac the influence of individual mono-O-acetylated sialic acids on bacterial and viral sialidases could be clearly shown. This extends and clarifies observations with glycoproteins containing mixtures of mono-, di- and higher O-acetylated sialic acids with substitution at the hydroxyls on carbons 4, 7, 8 and 9. A 4-O-acetyl substitution in sialic acids blocks the action of bacterial sialidases for substrates containing these derivatives, while viral enzymes show low but significant activity, reflected in Km and Vmax values. A small reduction in bacterial sialidase activity was observed for II3Neu5,9Ac2-Lac relative to II3Neu5Ac-Lac in agreement with kinetic analysis. Newcastle disease virus sialidase showed a 50% reduction in hydrolysis rate for the 9-O-acetylated substrate and ten-fold reductions of both Km and Vmax values.
D000818:Animals; D002417:Cattle; D003013:Clostridium / Q000201:enzymology; D006023:Glycoproteins / Q000378:metabolism; D006736:Horses; D066298:In Vitro Techniques; D007700:Kinetics; D009439:Neuraminidase / Q000378:metabolism*; D009522:Newcastle disease virus / Q000201:enzymology; D012471:Salivary Proteins and Peptides / Q000378:metabolism; D012794:Sialic Acids / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D006023:Glycoproteins; D012471:Salivary Proteins and Peptides; D012794:Sialic Acids; D009439:Neuraminidase