Table 1.

Mapping of disulphide bonds in Ero1α

Fractionsa	Treatmentsb		Peptidesc	Cysteinesd	Observed masse (MH+)	Mass differencef (MH+)
	DTE+IAA	Second digest
A	−	−	Cys35–Arg55	35, 37, 46, 48	2380.99	−3.95 (2 S-S)
	+	−	Cys35–Arg55	35, 37, 46, 48	2613.10	228.16 (4 IAA)
	−	AspN	Cys35–Asp44+Asp45–Cys48	35, 37, 46, 48	1570.54	−4.01 (2 S-S)
B	+	−	Arg83–Arg96	85, 94	1792.81	114.06 (2 IAA)
			Arg83–Arg97	85, 94	1948.90	114.05 (2 IAA)
			Tyr120–Arg136	131	2083.92	57.06 (1 IAA)
			Ile388–Arg398	391, 394, 397	1445.62	171.08 (3 IAA)
	−	AspN	Arg83–Asn89+Asp390–Arg398	85, 391, 394, 397	1944.88	−3.96 (2 S-S)
			Asp90–Arg96+Tyr120–Arg136	94, 131	2802.23	−1.97 (1 S-S)
			Asp90–Arg97+Tyr120–Arg136	94, 131	2958.34	−1.97 (1 S-S)
C	+	−	His158–Arg187	166	3493.53	57.06 (1 IAA)
			Ile199–Lys215	208	2182.12	57.05 (1 IAA)
			Arg216–Lys244	241	3282.52	56.98 (1 IAA)
			Arg216–Arg245	241	3438.50	56.85 (1 IAA)
	−	GluC	Ala176–Arg187		1431.74
			Tyr178–Arg187		1231.68
			Ile199–Glu206		1065.48
			Arg216–Glu230		1555.70
			Asn231–Glu238		1059.48
			Asn207–Lys215+Gly239–Glu243	208, 241	1595.75	−2.05 (1 S-S)
aFractions from the tryptic digest of Ero1α identified to contain disulphide-linked peptides.
bThe fractions were analysed by MS before and after reduction with DTE followed by alkylation with IAA. In some cases, the samples were further digested with endoproteinase AspN or endoproteinase GluC.
cPeptides identified by MALDI-TOF-MS.
dPositions of cysteines contained in the identified peptides.
eObserved monoisotopic molecular masses determined by MALDI-TOF-MS.
fDifference between observed and calculated masses. The number and type of modifications corresponding to the mass difference are given in parentheses: disulphide bridge (S–S) and alkylation with iodoacetamide (IAA).