Under specified conditions (pH = 6.8; T = 37 °C), α -glucosidase will catalyze the conversion of the substrate 4-nitrophenyl-α-D-glucopyranoside to α-D-glucopyranoside and p-nitrophenol, as shown below (Equation (1)). The yellow colour of the latter product is measured spectrophotometrically at 405 nm. [PNPG + α-glucosidase] → α-D-glucopyranoside + PNP (yellow)] Alpha-glucosidase inhibitors inhibit the absorption of carbohydrates from the small intestine. They competitively inhibit enzymes that convert complex nonabsorbable carbohydrates into simple absorbable carbohydrates. These enzymes include glucoamylase, sucrase, maltase, and isomaltase. By delaying carbohydrate absorption, they reduce the rise in postprandial blood glucose concentrations by about 3mmol/L.