46XANTHINE OXIDASE INHIBITORY ACTIVITY AND ENZYME KINETICS OF Polyalthia longifolia (Sonner.) Thw. LEAVES USING IN VITRO METHODThe present study was aimed at investigating the xanthine oxidase inhibitory activities of the ethanolic and chloroform extracts of the leaves of Polyalthia longifolia (Sonner.) Thw. (Annonaceae). The plant has been used in traditional system of medicine for the treatment of fever, skin diseases, diabetes, hypertension and helminthiasis and was reported to possess antibacterial, cytotoxic, antiulcer and antifungal activities. The degree of xanthine oxidase inhibition was determined in vitro by measuring the increase in absorbance at 295 nm associated with uric acid formation. The chloroform extract of P. longifolia leaves (PLCE) was found to possess more activity than that of the ethanol extract (PLEE) which can be confirmed by comparing the IC50 values of both the extracts, PLEE, showed half maximal inhibition at 65.3 ± 0.016 μg/ml whereas the PLCE, showed at 42.8 ± 0.024 μg/ml. The IC50 value of allopurinol was 29.2 ± 0.28 μg/ml. Lineweaver-Burk plot analysis of the enzyme kinetics for the extracts in comparison with standard allopurinol indicated that the mode of inhibition was of competitive type of inhibition. Xanthine oxidase is reported to be involved in the chronic complications associated with diabetes mellitus. The results of this present study suggest that the indicated use of leaves of Polyalthia longifolia for the treatment of diabetes in order to prevent its complications could be attributed to its XO inhibitory activity.tkchatterjee_81@rediffmail.comResearch312012Polyalthia longifolia,Xanthine oxidase,Xanthine dehydrogenase,Allopurinol,Uric acidAndichettiar Thirumalaisamy Sivashanmugam,Tapan Kumar ChatterjeeDivision of Pharmacology, Department of Pharmaceutical Technology, Jadavpur University, Kolkata, India,Division of Pharmacology, Department of Pharmaceutical Technology, Jadavpur University, Kolkata, India