Purification and characterization of ∼35 kDa antioxidant protein from curry leaves (Murraya koenigii L.)

Curry leaves (Murraya koenigii L. Spreng, Rutaceae) is an herbal species used in traditional medicine in eastern Asia. In this study, the antioxidant protein was purified by homogenization of curry leaves powder in Tris buffer, 65% ammonium sulphate precipitation and gel filtration on Sephadex G-75 column which resulted in three peaks (PI, PII and PIII). PII protein inhibited lipid peroxidation in human RBC ghost at 100 μg by 80%, whereas PI and PIII at 600 μg showed moderate antioxidant activity (40–50%). Homogeneity of PII was confirmed by rechromatographing on Sephadex G-75 and reverse phase HPLC. The antioxidant protein (PII) from curry leaves (APC) showed apparent molecular weight of 35 kDa by SDS–PAGE and MALDI/MS analysis. The protein nature of APC was established by the presence of amino acids and loss of antioxidant activity on heat and protease treatment. The APC at 0.8 μM inhibited lipoxygenase activity by 71%, effectively prevented diene, triene and tetraene lipids formation at 3 μM, and scavenged about 85% hydroxyl and DPPH radicals at 150-fold lesser concentration compared to BHA and α-tocopherol (400 μM). In addition, APC reduced cytochrome c and ferric ion, chelated ferrous ion, and inhibited ferrous sulfate: ascorbate-induced fragmentation and sugar oxidation to 80–90%. Thus, the present study demonstrates the in vitro characterization of antioxidant protein from the curry leaves (M. koenigii L.)