Alpha-glucosidase inhibitory activity of protein from seeds of djenkol bean Archidendron jiringa Nielsen

Abstract

The inhibitors of α-glucosidase enzyme from natural resource which is responding to digest carbohydrates to monosaccharides. It has been used for the treatment of diabetes mellitus type II or non insulin dependent diabetes mellitus. Legumes were reported as a major source of proteins and polypeptides with important biological activities. One of the biological activities in legume is α-glucosidase inhibitory activity. This study was attempted to isolate α-glucosidase inhibitors from two leguminous plants: Archidendron jiringa Nielsen. (Djenkol bean) and Parkia speciosa Hassk. (Stink bean). The potential α-glucosidase inhibitor was found in the protein extraction from seeds of A. jiringa when used Tris-HCl buffer for extraction then precipitated with 90% ammonium sulfate, and purify with affinity chromatography using ConA Sepharose as stationary phase. The bound protein gave inhibitory activity against α-glucosidase using p-nitrophenyl α-D-glucopyranoside (PNPG) with the IC₅₀ value of 0.031 mg protein. The molecular mass of the purified protein was 35.7 kDa, as estimated by SDS-PAGE. The protein was thermostable up to 80 °C for 70 min and showed an optimum activity within the pH range of 8.0-10.0. It has a high activity with divalent cations such as Cu²⁺, Zn²⁺ and Fe²⁺. The internal amino acid sequence of the protein showed that is similar to the sequences of lectin from Dioclea guainensis. Moreover, this α-glucosidase inhibitor has specific interaction with α-glucosidase enzyme which was confirmed by Surface Plasmon Resonance (SPR) technique.