A lectin extracted from Citrullus colocynthis L. (Cucurbitaceae) inhibits digestive α-amylase of Ectomyelois ceratoniae Zeller (Lepidoptera: Pyralidae)

A lectin was extracted from seeds of Citrullus colocynthis (Cucurbitaceae) by column chromatography using Sepharose 4BGalactose and DEAE-Cellulose fast flow. The inhibitory effects of the extracted lectin on digestive α-amylase of Ectomyelois ceratoniae larvae were studied using pH, temperature, time of incubation and kinetic parameters. Different concentrations of extracted lectin, Citrullus colocynthis agglutinin (CCA), inhibited digestive amylolytic activity by 22-49%. The highest inhibition was obtained at pH 8 and 9, which corresponds with the highest enzymatic activity in the control. The highest inhibition of E. ceratoniae α-amylase was found at 40°C, which corresponds with the optimal temperature for enzymatic activity. Timecourse experiments revealed the highest amylolytic activity at 20-40 min post-incubation, while the highest inhibition was found after 20- 30 min. Kinetic analysis showed that incubation of α-amylase with CCA significantly decreased V_max, indicating non-competitive inhibition, but no statistical difference was found in the K_m value. Our results indicated that CCA significantly inhibited activity of digestive α-amylase in E. ceratoniae larvae, suggesting its possible application as a potential alternative control method against this pest.