An alpha-glucosidase inhibitory activity of thermostable lectin protein from Archidendron jiringa Nielsen seeds

Abstract

Inhibitors of α-glucosidase from natural resources that inhibit the digestion of carbohydrate polymers into monosaccharides in the gut are used in the treatment of insulin-independent diabetes mellitus type 2. Archidendron jiringa belongs to pea family of leguminous plants, some of which are a source of interesting bioactivities, including α-glucosidase inhibitory (GI) activity. A novel GI lectin was enriched from the seeds of the Djenkol bean, A. jiringa, to apparent homogeneity by 90% saturation ammonium sulfate precipitation and Con A-Sepharose affinity column chromatography. This lectin had an IC₅₀ value for GI activity of 0.031 „b 0.02 mg/ml, an estimated molecular mass of 35.7 kDa, of which 15.8% was carbohydrate, was thermostable up to 80¢XC for 70 min, showed an optimum activity within the pH range of 8.0 to 10.0 and a high activity with some divalent cations such as copper (Cu²⁺) and high levels (50 to 100 mM) of zinc (Zn²⁺) and iron (Fe²⁺). The sequence of an internal 16 amino acid fragment of the protein showed 100% identity to the mannose-glucose specific lectin precursor of Dioclea guainensis. The GI lectin had a high specific interaction with α-glucosidase (affinity constant = 9.3773 „e 10-7 s^-1, Ks = 0.0241 s^-1, Ka = 2.39 „e 103 s^-1M^-1 and Kd = 0.0117 M).

Key words: Archidendron jiringa, α-glucosidase inhibitors, lectin.