Mass spectrometric analysis of glucose-modified ribonuclease

RNase A (1 mM) was incubated with glucose (0.4 M) at 37°C for up to 14 days in phosphate buffer (0.2 M, pH 7.4), digested with trypsin and analysed by LC-MS. The major sites of fructoselysine formation were Lys¹, Lys⁷, Lys³⁷ and Lys⁴¹. Three of these sites (Lys⁷, Lys³⁷ and Lys⁴¹) were also the major sites of N^∊-(carboxymethyl)lysine formation.