Abstract: Objective Acer truncatum bunge is a prominent species of Acer in the hardwood forests of north China.It has been used as a Chinese folk medicine for the treatment of coronary atherosclerosis,cerebrovascular diseases and angina pectoris.Animal fatty acid synthase(E.C.2.3.l.85,FAS) plays an important role in fatty acid synthesis.It was reported that FAS is selectively highly expressed in certain human cancer cells,including carcinomas of the breast,prostate,colon,ovary,endometrium and lung.FAS has been suggested as a potential new therapeutic target in the treatment of cancer and FAS inhibitors may be developed into new chemotherapeutic methods.The extracts from Aceraceae leaves are found to possess a high inhibitory activity against FAS and the correlated antitumor bioactivity has also been proved in our experiment.To examine the inhibitory activity of the leaves gathered in different seasons and the correlation with the total flavonoids content,we perform the following experiment.Methods By using colorimetric methods,the content of total flavonoids in leaves of Acer truncatum bung of different seasons was determined.The assay for FAS activity which had been described previously was performed with a Shimadzu UV2550 double wavelength/double beam spectrophotometer at 37 ℃ by following the decrease of NADPH at 340 nm.The reaction system contained 0.1 mol/L potassium phosphate buffer,pH 7.0;1.0 mol/L EDTA;1.0 mmol/L DTT;3 mmol/L acetyl-CoA;10 mmol/L malonyl-CoA;32 mmol/L NADPH and duck liver FAS 10 microg in a total volume of 2.0 mL.Results The inhibitory ability against FAS and the content of total flavonoids exhibited a positive correlation for the extract from the leaves of May,June,July,prepared with the solvent rich in ethanol.Otherwise,the correlation would not exist.Conclusion The inhibitory ability of leaves of Acer truncatum bunge at different seasons markedly differed and the extracts from the fallen leaves possess stronger inhibitory effect on FAS.It may become a more efficient,new natural source of FAS inhibitor and could find a wide application in the field of health care.

Key words: Acer truncatum bunge, fatty acid synthase, FAS, total flavonoids