RESUMEN
Currently available enzymatic methods for the measurement of glycated proteins utilize fructosyl amino acid/peptide oxidases (FAOXs/FPOXs) as sensing elements. FAOXs/FPOXs oxidize glycated amino acids or glycated dipeptides but they are not able to accept longer glycated peptides or intact glycated proteins as substrates. Therefore, pretreatment via proteolytic digestion is unavoidable with the current enzymatic methods, and there remains a need for simpler measurement methods for glycated proteins. In this study, in order to develop a novel sensing system for glycated albumin (GA), a marker for diabetes, with no requirement for proteolytic digestion, we created an electrochemical sensor based on fructosamine 6-kinase (FN6K) from Escherichia coli. Uniquely, FN6K can react directly with intact GA unlike FAOXs/FPOXs. The concentration of GA in samples was measured using a carbon-printed disposable electrode upon which FN6K as well as two additional enzymes, pyruvate kinase and pyruvate dehydrogenase were overlaid. A clear correlation between the response current and the concentration of GA was observed in the range of 20-100 µM GA, which is suitable for measurement of GA in diluted blood samples from both healthy individuals and patients with diabetes. The sensing system reported here could be applied to point-of-care-testing devices for measurement of glycated proteins.