Isolation and characterization of α-amylase inhibitor from Leucas aspera (Willd) Link: α-amylase assay combined with FPLC chromatography for expedited identification

The aim of the present study was to isolate and characterize a proteinaceous α-amylase inhibitor from the whole plant extract of Leucas aspera (Willd) Link. The proteins were further purified by fast and reliable ion-exchange chromatography. A ~ 28 kDa protein from L. aspera inhibited the activity of fungal α-amylase by 90% at 80:1 (inhibitor:enzyme) ratio. The inhibition activity was examined in various α-amylases and its enhanced inhibition activity was witnessed. The activity of the inhibitor on α-amylase was stable and high at pH 6–7 and at temperatures of 30–50 °C. The high-resolution α-amylase inhibition assay/FPLC-MS-SPE platform allowed identification of 28 kDa protein with high purification fold as the α-amylase inhibitor in L. aspera and peptides were matched with highest score of alpha-amylase/trypsin inhibitor of Zea mays. In conclusion, results here obtained suggested that the primary metabolites (proteins) in L. aspera are mainly responsible for its versatile biological and pharmacological activities.