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Modification and Cross-Linking of Proteins by Glycolaldehyde and Glyoxal: A Model System

Klaus, Alexander, Rau, Robert, Glomb, Marcus A.
Journal of agricultural and food chemistry 2018 v.66 no.41 pp. 10835-10843
Maillard reaction, aldehydes, crosslinking, gel chromatography, ion exchange chromatography, isoelectric focusing, isoelectric point, models, molecular weight, phenylalanine, polyacrylamide gel electrophoresis, proteins, ribonucleases, sodium dodecyl sulfate
Highly reactive intermediates of the Maillard reaction, such as glycolaldehyde and glyoxal, are precursors in the modification and cross-linking of proteins. Therefore, we investigated ribonuclease A modified by glycolaldehyde and glyoxal, separately. For the first time, various protein species derived by these aldehydes were successfully separated by ion-exchange chromatography and gel permeation chromatography. Highly cross-linked ribonuclease A was obtained in glycolaldehyde incubations. In contrast, glyoxal predominantly led to modified monomeric protein species. These results were verified by sodium dodecyl sulfate polyacrylamide gel electrophoresis and isoelectric focusing. Quantitation of mono- and bivalent protein modifications of the isolated protein species led to a positive correlation between the degree of protein modification and the change of the isoelectric point and molecular weight, respectively. Glycolaldehyde is easily oxidized to glyoxal. However, significantly lower levels of bivalent glyoxal modifications were detected in glycolaldehyde versus glyoxal incubations (glyoxal–lysine dimer, 1.58 ± 0.02 versus 2.86 ± 0.04 mmol/mol of phenylalanine; glyoxal–lysine amide, 2.7 ± 0.1 versus 5.6 ± 0.1 mmol/mol of phenylalanine). In addition, a novel glycolaldehyde-specific lysine–lysine cross-link was identified and putatively assigned as 1-(5-amino-5-carboxypentyl)-4-(5-amino-5-carboxypentyl-amino)pyridinium salt.