Table 3.

Residues in RhoGDI-α Photolabeled by 3-Azioctanol and 3-Azibutanol Identified in Peptide Fragments Following Trypsinolysis and LTQ–FT Mass Spectrometry.

Agent	[Alcohol] µMa	AGGC	Residue Photolabeled	Peptideb	Charge	Rt, min	Xcorr	MH+c	Accuracyd ppm
3-azibutanol	100	+	E193	[1]	+3	23.45	5.29	2437.60	2.46
	100	–		Photolabeled peptide not detected
3-azibutanol	100	+	E163	[2]	+2	22.52	5.06	1824.96	3.28
	100	–		Photolabeled peptide not detected
3-azioctanol	10	+	E163	[2]	+2	18.82	2.95	1880.90	0.00
	10	–		[2]	+2	18.84	4.30	1880.90	0.00
Unlabeled peptide f		–	E193	[1]	+3	16.15	4.77	2365.54	0.00
		–	E163	[2]	+2	21.02	4.75	1752.89	0.00

^aLowest 3-azialcohol concentration where photoincorporation was detected.

^bPeptides photolabeled by 3-azialcohols: [1]=RhoGDIα(181–199)=FTDDDKTDHLSWEWNLTIK; [2]= RhoGDIα(153–167)=AEEYEFLTPVEEAPK. Photolabeled residues are indicated in bold.

^cRepresentative observed masses which include increases due to photolabeling by 3-azioctanol (128 Dalton) or 3-azibutanol (72 Dalton).

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

^fUnlabeled peptides are those derived from that fraction of RhoGDIα which was not photolabeled during the experiment with 100 µM azibutanol in the presence of AGGC. See “EXPERIMENTAL PROCEDURES” section for other details