Glycosylated salivary α-amylases are capable of maltotriose hydrolysis and glucose formation

Abstract

The physiological and/or clinical significance of sugar chains in human salivary αamylase was investigated in terms of substrate-specificity for synthesized malto-oligosaccharides. Glycosylated and non-glycosylated α-amylases were prepared on a Sephacryl S-200 column, in which the amylases were separated into four fractions from the different affinities for Sephacryl: fraction I, amylases bearing sugar chains with sialic acid; fraction II, amylases bearing sugar chains without sialic acid; fractions III and IV, non-glycosylated amylases. These were classified according to the differences in their affinities for lectins, molecular sizes and isoelectric points. The inhibitory effect of maltotriose (G 3) on starch hydrolysis of the amylase fraction, suggests that starch and G 3 can be the substrate for glycosylated amylase, and that the glycosylated amylases are capable of G 3 hydrolysis for conversion into maltose and glucose. Using malto-oligosaccharides, G 3, G 4, G 5 and G 7, as substrates, the substrate-specificities and G 3/G 5 ratio of amylase activities in the four fractions were examined. Maltopentaose, G 5, is routinely used as a substrate for α-amylase, and then we assumed that both glycosylated and non-glycosylated amylases react with G 5. Moreover, the results indicate that the glycosylated amylases clearly had a higher capacity for G 3 hydrolysis than the non-glycosylated amylases, although no substrate preference of either type of amylase was observed among G 4, G 5 and G 7. Glycosylated amylases have the capacity for glucose formation from malto-oligosaccharides.