Table 1.

Assessment of guanidination efficiency of lysine ε-amines under different conditions (Spectral count of identified peptides was used for the estimation).

Samples	Incubation conditions	Identified peptides	Lysine-containing peptides	Guanidinated lysine-peptides	Guanidination efficiency
Bovine serum albumin	4° C, 24 h	473	262	260	99.2%
Bovine serum albumin	37° C, 4 h	310	148	145	98.0%
Bovine serum albumin	65° C, 20 min	839	440	207	47%
Aspergillus nigerlysate	4° C, 24 h	2,725	1,300	1,290	99.2%

^*All reactions were performed at pH 10.5. The number of identified peptides indicates all identified MS/MS spectra with FDR <0.5%.