Evaluation of α-glucosidase inhibition by using an immobilized assay system

The inhibitory effects of natural and synthetic inhibitors on the intestinal membrane-bound hydrolase, α-glucosidase (AGH), were evaluated by using an immobilized cyanogen bromide-activated Sepharose 4B support. Immobilized AGH (iAGH) inhibition study by synthetic inhibitors (acarbose and voglibose) revealed that the magnitude of inhibition differed from that in the free AGH (fAGH) study: IC₅₀ value of acarbose in iAGH-maltase assay system, 340 - 430 nM; fAGH, 11 nM. iAGH-maltase inhibition by both inhibitors was influenced by blocking reagents with different functional groups (COOH, OH, CH₃, and NH₂ groups). On the other hand, significant iAGH-sucrase inhibitory activity was observed only when using the negatively charged support induced by 0.1 M β-alanine. The K(m) values obtained in the iAGH assay system were similar to those from the fAGH method. With natural inhibitors, the iAGH-sucrase inhibitory activity of D-xylose, with in vivo glucose suppression, increased twice compared to that in fAGH. Green tea extract gave almost the same inhibition for both AGH assay systems.