TABLE 1.

The Cys²²⁰–Cys²⁴⁸ disulfide bond in βII-tryptase is reduced in a fraction of the molecules, and the oxidized fraction can be reduced by thioredoxin

The fraction of peptides containing Cys²²⁰ or Cys²⁴⁸ that labeled with IAM increased upon addition of thioredoxin (bold face type), indicating reduction of the Cys²²⁰–Cys²⁴⁸ disulfide bond. Thioredoxin selectively reduced this bond because there was no appreciable change in the IAM labeling of the other six cysteines in the protease (Cys⁵⁹–Cys⁷⁵, Cys¹⁵⁵–Cys²³⁰, and Cys¹⁸⁸–Cys²¹¹). MMTS, methyl methanethiolsulfonate.

Digestion	βII-Tryptase peptide	Cys	No thioredoxin			With thioredoxin
			Abundance		Percentage reduced	Abundance		Percentage reduced
			IAM adduct	MMTS adduct		IAM adduct	MMTS adduct
Chymotrypsin	CGGSLIHPQW	59	60,999	287,060	18	402,680	127,741	25
Trypsin	TAAHCVGPDVK	75	28,314	600,511	5	18,112	384,333	5
Trypsin	VPIMENHICDAK	188	5,788,350	23,433,269	20	4,242,676	14,492,330	23
Trypsin	IVRDDMLCAGNTR	211	1,580,273	9,798,215	14	1,067,604	5,531,002	16
Trypsin	DSCQGDSGGPL	220	146,813	474,108	24	176,254	43,489	80
Trypsin	DSCQGDSGGPLVCK	230	775,247	11,931,392	6	433,216	6,693,478	6
Chymotrypsin	GEGCAQPNRPGIY	248	643,460	1,302,075	33	1,885,816	354,137	84