Hydrolysis by human alpha-amylase of p-nitrophenyloligosaccharides containing four to seven glucose units.

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Abstract
Kinetic and "high-pressure" liquid-chromatographic studies were performed on the reaction of human pancreatic and salivary alpha-amylase (EC 3.2.1.1) with p-nitrophenyloligosaccharides containing four to seven glucose units. The kinetic studies indicate that, as the temperature increases from 25 to 37 degrees C, the apparent Km of the enzyme for a given substrate increases slightly. However, as the number of glucose units in the substrate increases, the apparent Km decreases. The apparent Vmax increases as the temperature increases, and decreases as the number of glucose units in the substrate increases. In contrast, chromatographic data indicate that the relative rate of hydrolysis by alpha-amylase is pG7 greater than pG6 greater than pG5 greater than pG4. The differences between the kinetic and the chromatographic results are discussed. p-Nitrophenyl-alpha-maltopentaoside and p-nitrophenyl-alpha-maltohexaoside are superior to the other p-nitrophenyloligosaccharides as substrates for determining alpha-amylase activity in an alpha-glucosidase-coupled assay system.