Glycation of N-ε-carboxymethyllysine

• Published in: European food research & technology 2022-03, Vol.248 (3), p.825-837
• Main Authors: Hellwig, Michael, Nitschke, Julia, Henle, Thomas
• Format: Article
• Language: English
• Subjects: Agriculture; Amadori compounds; Amino acids; Analytical Chemistry; Biotechnology; Bovine serum albumin; Carboxymethyllysine; Chemistry; Chemistry and Materials Science; Chromatography; E coli; Food; Food Science; Forestry; Galactose; Glucose; Glycosylation; High-performance liquid chromatography; Hydrochloric acid; Lactose; Liquid chromatography; Lysine; Maillard reaction; Maltose; NMR; Nuclear magnetic resonance; Original Paper; Proteins; Ribose; Serum albumin; Sugar
• ISSN: 1438-2377; 1438-2385
• DOI: 10.1007/s00217-021-03931-7

The Maillard reaction is traditionally subdivided into three stages that start consecutively and run in parallel. Here, we show that N -ε-carboxymethyllysine (CML), a compound formed in the late stage of the reaction, can undergo a second glycation event at its secondary amino group leading to a new class of Amadori rearrangement products. When N -α-hippuryl-CML was incubated in the presence of reducing sugars such as glucose, galactose, ribose, xylose, maltose, or lactose in solution for 1 h at 75 °C, the compound was degraded by 6–21%, and N -ε-carboxymethyl- N -ε-deoxyketosyl lysine derivatives were formed. Under the same conditions, lysine was 5–10 times more reactive than CML. N -α-hippuryl- N -ε-carboxymethyl- N -ε-(1-deoxyfructosyl)- l -lysine (hippuryl-CMFL) and N -ε-carboxymethyl- N -ε-(1-deoxyfructosyl)- l -lysine (CMFL) were synthesized, isolated and characterized by MS/MS and NMR experiments. Depending on the reaction conditions, up to 21% of CMFL can be converted to the furosine analogue N -ε-carboxymethyl- N -ε-furoylmethyl- l -lysine (CM-Fur) during standard acid protein hydrolysis with hydrochloric acid. Incubation of bovine serum albumin (BSA) with glucose for up to 9 weeks at 37 °C revealed the formation of CMFL in the protein as assessed by HPLC–MS/MS in the MRM mode. Under these conditions, ca. 13% of lysine residues had been converted to fructosyllysine, and 0.03% had been converted to CMFL. The detection of glycation products of glycated amino acids (heterogeneous multiple glycation) reveals a novel pathway in the Maillard reaction.