L tryptophan

All chemicals and solvents were of analytical or HPLC grade. Water, methanol, acetonitrile, formic acid were purchased from CNW Technologies GmbH (Düsseldorf, Germany). L-2-chlorophenylalanine was from Shanghai Hengchuang Bio-technology Co., Ltd. (Shanghai, China). L-tryptophan was purchased from Sangon (Shanghai, China), and L-kynurenine from Macklin (Shanghai, China).

The GST-IDO1 gene was cloned by Shanghai Generay Biotech Co. Ltd (Shanghai, China). The BL21(DE3) cells were obtained from TransGen Biotech Co. Ltd (Shanghai, China). Ampicillin, isopropyl β-D-thiogalactoside (IPTG), 5-Aminolevulinic acid (5-ALA), phenylmethanesulfonyl fluoride (PMSF), DNase I (from bovine pancreas), reduced glutathione, L-tryptophan, ascorbic acid, methylene blue, catalase, and sodium dithionite were obtained from Sangon Biotech (Shanghai, China) Co. Ltd. DMSO was purchased from Sigma-Aldrich. The CCK8 kit was purchased from Beyotime Biotechnology Co. Ltd.(Shanghai, China). Glutathione agarose beads were purchased from Changzhou Smart-Lifesciences Biotechnology Co. Ltd. (Changzhou, China) PD-10 desalting column was purchased from GE Healthcare Biosciences. HRV 3C Protease was purchased from Sino Biological Inc. (Shanghai, China). Cancer cell lines were purchased from the Cell Bank of Chinese Academy of Sciences. The experimental compounds were provided by Professor Zhao (Shanghai Institute of Organic Sciences, Chinese Academy of Sciences). All chemicals of analytical and reagent grade were obtained from commercial sources and used without further purification.

L-cysteine (Cys), L-histidine (His), L-leucine (Leu), L-lysine hydrochloride (Lys), L-methionine (Met), L-phenylalanine (Phe), L-proline (Pro), L-tryptophan (Trp), L-tyrosine (Tyr) were purchased from Sangon Biotech Corp. (shanghai, China). Acetonitrile was obtained from Wako Pure Chemical Industries, Ltd (Osaka, Japan). Ultra-pure water was collected from a Milli-Q SP TOC system water purifier (Millipore Corp., Bedford, MA, USA). All amino acid samples were dissolved in ultra-pure water till the concentration reached 1 mmol/L. Then, 50 ml of amino acid solution was transferred to the discharge vessel at room temperature for plasma treatments which were performed at V_P = 4.0 kV within different treatment periods.