Table 1. Residues photolabeled in a tryptic fragment of Japanese Firefly Luciferase (306-YDLSNLVEIASGGAPLSK-323)^a identified by LTQ–FT mass spectrometry and MSMS.

Agent	Alcohol µM	ATP	Time ms	Residue Photolabeled	Charge	R t, min	Xcorr	bMH+	Accuracycppm
Parent peptided					+2	24.0	6.0	1835.05	0.91
7-azioctanol	100	+	200	E313f	+2	31.2	5.5	1963.17	0.79
	100	−	∞	E313	+2	26.1	5.4	1963.17	0.79
	100	+	∞		Photolabeled peptide rarely detected
3-azioctanol	100	+	200	E313	+2	29.1	5.9	1963.17	0.79
	100	−	∞	E313	+2	28.1	5.4	1963.17	0.79
	100	+	∞		Photolabeled peptide rarely detected
3-azibutanol	1000	+	200	E313f	+2	26.6	5.6	1907.05	0.91
	1000	−	∞	E313	+2	23.5	6.1	1907.05	0.91
	1000	+	∞		Photolabeled peptide not detected
TFD-benzyl alcohol	100	+	200	I314	+2	30.5	4.4	2022.00	1.96
	100	+	200	S316	+2	29.3	5.4	2022.00	1.96
	100	−	200	I314	+2	31.2	5.6	2022.00	1.96

^aPhotolabeled residues are indicated in bold.

^bRepresentative observed masses that include increases due to photolabeling by 3-azioctanol and 7-azioctanol (128 Da) or 3-azibutanol (72 Da) or TFD-benzyl alcohol (188 Da).

^cAccuracy is the difference between the calculated and observed mass expressed in ppm.

^dParent peptides are those derived from that fraction of Luciferase in a given run that was not photolabeled during an experiment with azialcohols or TFD-benzyl alcohol. See “Materials and methods” section for other details.