Table 5.

Analytical techniques/assays to detect Trp oxidation products with the corresponding analytical techniques and relevant references.

Amino Acid Residue	Oxidized Amino Acid Residues	Analytical Technique	Reference
Trp	Loss of Trp residue	Fluorescence spectroscopy	Davies et al. (1999), Lakowicz et al. (2006), Dalsgarrd et al. (2007), Paz et al. (2012) [260,270,271,272]
	NFK, Kyn, 5-OH-Trp	HPLC-RP	Simat et al. (1998), Yang et al. (2007) [273,274]
	NFK, Kyn	Fluorescence spectroscopy	Fakunaga et al. (1982), Ehrenshaft et al. (2015) [188,275]
	NFK, Kyn, 3-OH-Trp	Raman spectroscopy with principal component analysis	McAvan et al. (2020) [229]
		CD spectroscopy with principal component analysis	McAvan et al. (2020) [229]
	NFK, Kyn, 3-OH-Kyn	ESI-LCMS	Domingues et al. (2003), Perdivara et al. (2010) [276,277]
	NFK, Kyn	NMR	Hinterholzer et al. (2020) [230]
		Antiserum	Staniszewska et al. (2007), Ehrenshaft el al (2009) [278,279]
	Di-Trp	UV and Fluorescence spectroscopy	Hawkins et al. (2009) [280]
		18O-labeling MS spectroscopy	Medinas et al. (2010), Mariotti et al. (2018) [185,252]