Inhibitory potentials and kinetics of the inhibition of carbohydrate-hydrolysing enzymes by the pod and seed extracts of Lessertia montana (Fabaceae) E. Phillips & R.A. Dyer

ABSTRACT

The study evaluated the effect of extracts of the seeds and pod parts of Lessertia montana on diabetes and freeradicals. Free radical scavenging activities of the extracts was tested against 1,1-diphenyl-2-picrylhydrazyl (DPPH),nitric oxide, 2,2-azinobis (3-ethylbenzothiazoline-6) sulphonic acid (ABTS), hydroxyl radical and reducing power,metal chelating assays, while the antidiabetic activity was assessed via the inhibition and kinetics of α-amylase andα-glucosidase. The pod decoction extract revealed the best radical scavenging activities in DPPH, ABTS, and metalchelating (with IC50 values 1,371, 730, and 798 µg/ml, respectively) compared with other extracts and control havingan IC50 (3,094, 4,125, and 523 µg/ml, respectively) values. While the aqueous ethanolic extract for both parts exhibitedthe highest reducing capabilities of 2.969 (pod) and 3.457 (seeds) at 1 mg/ml, the aqueous extract of the seed showedthe best inhibitory activities in two of the six tested assays, namely, hydroxyl radical (717 µg/ml) and metal chelating(59 µg/ml). The kinetics of inhibition of α-amylase and α-glucosidase by aqueous ethanolic extract of the pod wascompetitive and non-competitive, respectively, while the two enzymes were uncompetitively inhibited by ethanolicextract of the seed. The investigation corroborated the antioxidative and antidiabetic potentials of the leaf as previouslyestablished from our group.