2.1. Chemicals and Reagents

Alcalase^® 2.4 L FG was purchased from Novozymes (Bagsvaerd, Denmark). Pepsin (from porcine gastric mucosa), pancreatin (from porcine pancreas), 3-morpholinosydnonimine hydrochloride (SIN-1), dihydrorhodamine 123 (DHR 123, ≥95.0%), fluorescein sodium salt (FL, BioReagent), 2,4,6-trinitrobenzenesulfonic acid solution (TNBS, 5.0%, w/v, BioReagent), reduced L-glutathione (GSH, ≥98.0%), cytochrome C, aprotinin, hippuryl-His-Leu acetate salt (Hip-His-Leu), 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS, ≥98.0%), 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-p,p′-disulfonic acid monosodium salt hydrate (ferrozine, 97.0%), (±)-6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox, 97.0%), 2,4,6-tris(2-pyridyl)-s-triazine (TPTZ, ≥99.0%), 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT), and 2′7′-dichlorodihydro-fluorescein diacetate (DCFH-DA) were purchased from Sigma-Aldrich (St. Louis, MO, USA). 2,2′-Azobis (2-methylpropionamidine) dihydrochloride (AAPH, 98.0%) and tryptophan (99.0%) were bought from ACROS Organics™ (Morris Plains, NJ, USA). L(+)-ascorbic acid was obtained from CARLO ERBA Reagents S.A.S (Rodano, Italy). The synthetic peptides, AGNQVLNLQADLPK (AK-14) and NTFLFFK (NK-7), were obtained from GL Biochem (Shanghai) Ltd. (Shanghai, China). Dulbecco’s modified eagle medium (DMEM) and fetal bovine serum (FBS) were purchased from HyClone (HyClone, Logan, UT, USA). Trypsin-ethylenediaminetetraacetic acid (EDTA), L-Gln, and non-essential amino acids (NEAAs) were obtained from Gibco (Carlsbad, CA, USA) for the cell culture studies. Acetonitrile (ACN) and trifluoroacetic acid (TFA) were of HPLC grade. All the other chemicals were of analytical grade.