Turmerin, the antioxidant protein from turmeric (Curcuma longa) exhibits antihyperglycaemic effects

Abstract

A wide range of proteinaceous inhibitors are present in plants to protect themselves from hydrolytic enzymes. In this study, turmerin, a water-soluble peptide in turmeric rhizomes, was evaluated for its inhibitory potential against glucosidase and its antioxidant (AO) capacity. Turmerin inhibited -amylase and -glucosidase activities with IC50 values 31 and 192 mgmL 1, respectively. Under the experimental conditions, those values for a standard glucosidase inhibitor,acarbose, were 81 and 296 mgmL 1, respectively. The AO capacity of turmerin was evaluated using in vitro assay systems. Turmerin showed good DPPH (IC50¼29 mgmL 1) and superoxide (IC50¼48 mgmL 1) and moderate ABTS(IC50¼83 mgmL 1) radical scavenging and Fe(II) chelation (IC50¼101 mgmL 1)capacities. The inhibitory potential showed by turmerin against enzymes linked to type 2 diabetes, as well as its moderate AO capacity, could rationalise the traditional usage of turmeric rhizome preparations against diabetes