Serine

Carbamazepine (CBZ, >98% purity),
sulfadimethoxine (SDM, >98% purity), trimethoprim (TMP, >98%
purity),
all test amino acids (i.e., glycine, alanine, serine, leucine, proline,
phenylalanine, glutamic acid, asparagine, and histidine), phenyl methyl
sulfoxide (PMSO), phenyl methyl sulfone (PMSO₂), sodium
thiosulfate, and sodium borate were purchased from Fisher Scientific
(Austin, Texas, USA). A wet chemical procedure was applied to prepare
solid potassium ferrate(VI) (K₂FeO₄),^{59 (link)} which had a purity of more than 90%. The solid
K₂FeO₄ was dissolved in a 0.01 M sodium borate
buffer solution. The concentration of Fe(VI) solution was determined
by measuring the absorbance at 510 nm using a 1.0 cm path length and
a molar absorption coefficient of ε_510nm = 1150 M^–1 cm^–1,^{59 (link)} with a UV–visible spectrometer (Thermo Scientific Co., USA).
All reaction solutions were prepared using Milli-Q ultrapure water
(>18 MΩ cm^–1 resistivity, Millipore, Milford,
USA).

NOS1, Saos2, U2OS, and MNNG were cultured in MEM (Cat # 11095072, GIBCO, Thermo Fisher, Waltham, MA) supplemented with 10% FBS (Cat # S11150, R&D Systems, Bio-Techne, Minneapolis, MN), 1.3% penicillin/streptomycin (Cat # 15140122, GIBCO, Thermo Fisher, Waltham, MA), 286 μM serine (Cat # AAJ6218709, Fisher Scientific, Hampton, NH) and 286 μM glycine (Cat # 67419, Sigma-Aldrich, St. Louis, MO). MG63, MDA-MB-231, and MDA-MB-468 were cultured in DMEM (Cat # 11965084, GIBCO, Thermo Fisher, Waltham, MA) supplemented with 10% FBS and 1.3% penicillin/streptomycin. All cells were maintained at 37°C and 5% CO₂ in a humidified atmosphere. All cells were cultured in prophylactic plasmocin (Cat # ant-mpp, InvivoGen, San Diego, CA) and checked regularly for mycoplasma contamination.