Table 2.

Summary of peptide fragments observed in MALDI-TOF mass spectra of a CTB tryptic digest.

Fragment (amino acid start-end)	Sequence	Calculated MH+ (Da)	occurrence frequency*	Confirmed by MS/MS?
64-67#	(K)AIER(M)	488.28	3/4
70-73	(K)DTLR(I)	504.28	1/4
64-69 (1 Oxidation) or 68-73#	(K)AIERMK(D) or (R)MKDTLR(I)	763.41	3/4
68-73 (1 Oxidation)	(R)MKDTLR(I)	779.4	3/4
74-81#	(R)IAYLTEAK(V)	908.51	3/4
36-43#	(R)EMAIITFK(N)	952.52	4/4
35-43	(K)REMAIITFK(N)	1108.62	1/4
35-43 (1 Oxidation)	(K)REMAIITFK(N)	1124.61	4/4
24-34#	(K)IFSYTESLAGK(R)	1215.62	4/4	Y
24-35	(K)IFSYTESLAGKR(E)	1371.72	4/4	Y
44-62#	(K)NGATFQVEVPGSQHIDSQK(K)	2041.99	4/4	Y
44-63	(K)NGATFQVEVPGSQHIDSQKK(A)	2170.09	4/4

^*Occurrence frequency is the number of samples in which the fragment peak appeared/total samples. Four samples were analyzed.

^#These peptides were also detected by van Baar et al. [39]