TABLE 3.

Peptides treated with β-propiolactone at different pH values

Peptide	Sequence	Mass	Adductsa	ΔMb	Conversionc
					pH 3.0	pH 5.0	pH 7.0	pH 9.0
		Da		Da	%
1	Ac-VTLAVTR-NH2	799.492	0d	–e	–e	–	–	0.3 ± 0.1
2	Ac-VTLCVTR-NH2	831.464	4	72/144	–	8.4 ± 2.2	98.5 ± 0.4	98.6 ± 00
3	Ac-VTLDVTR-NH2	843.481	2	72/144	1.8 ± 0.3	4.2 ± 0.2	9.2 ± 1.2	8.0 ± 0.7
4	Ac-VTLEVTR-NH2	857.497	2	72/144	0.8 ± 0.1	2.8 ± 0.1	7.7 ± 1.1	10.8 ± 2.3
5	Ac-VTLHVTR-NH2	865.513	2	72/144	–	0.3 ± 0.0	15.5 ± 0.4	25.0 ± 0.7
6	Ac-VTLKVTR-NH2	856.549	2	72	–	–	0.7 ± 0.2	5.8 ± 0.4
7	Ac-VTLMVTR-NH2	859.495	2	72/144	58.7 ± 2.8	50.7 ± 3.2	37.6 ± 1.2	36.4 ± 4.0
8	Ac-VTLNVTR-NH2	842.497	0	–	–	–	–	0.5 ± 0.1
9	Ac-VTLQVTR-NH2	856.513	0	–	–	–	–	1.0 ± 0.1
10	Ac-VTLSVTR-NH2	815.487	1	72	–	–	0.2 ± 0.0	2.2 ± 0.1
11	Ac-VTLWVTR-NH2	914.534	0	–	–	–	–	0.2 ± 0.0
12	Ac-VTLYVTR-NH2	891.518	1	72	–	–	2.7 ± 0.1	14.7 ± 0.3

^a The number of β-propiolactone adducts attached to the residue in bold (X) are given in bold. Reaction products were identified based on the number of peaks in HPLC chromatograms and MS² data.

^b Mass increments of peptides in phosphate buffers of pH 7.0 are observed after treatment with β-propiolactone.

^c Data are the mean ± S.D.; n = 3.

^d The alanine residue is not modified. However, two reaction products were found in which one of the threonine residues was slightly modified by β-propiolactone at a pH of 9.0.

^e No reaction products of β-propiolactone were detected.