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

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 alpha-amylase and alpha-glucosidase activities with IC50 values 31 and 192 mu g mL(-1), respectively. Under the experimental conditions, those values for a standard glucosidase inhibitor, acarbose, were 81 and 296 mu g mL(-1), respectively. The AO capacity of turmerin was evaluated using in vitro assay systems. Turmerin showed good DPPH (IC50 29 mu g mL(-1)) and superoxide (IC50 48 mu g mL(-1)) and moderate ABTS (IC50 83 mu g mL(-1)) radical scavenging and Fe(II) chelation (IC50 101 mu g mL(-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.