Determination of Fructosyl Amino Acids and Fructosyl Peptides in Protease-digested Blood Sample by a Flow-Injection System with an Enzyme Reactor

A comprehensive review on fructosyl peptide oxidase as an important enzyme for present hemoglobin A1c assays

Glycated proteins are generated by binding of glucose to the proteins in blood stream through a nonenzymatic reaction. Hemoglobin A1c (HbA1c) is a glycated protein with glucose at the N-terminal of β-chain. HbA1c is extensively used as an indicator for assessing the blood glucose concentration in diabetes patients. There are different conventional clinical methods for the detection of HbA1c. However, enzymatic detection method has newly obtained great attention for its high precision and cost-effectiveness. Today, fructosyl peptide oxidase (FPOX) plays a key role in the enzymatic measurement of HbA1c, and different companies have marketed HbA1c assay systems based on FPOX. Recent investigations show that FPOX could be used in assaying HbA1 without requiring HbA1c primary digestion. It could also be applied as a biosensor for HbA1c detection. In this review, we have discussed the recent improvements of FPOX properties, different methods of FPOX purification, solubility, and immobilization, and also the use of FPOX in HbA1c biosensors.

1-Amino-1-deoxy-d-fructose ("fructosamine") and its derivatives

Fructosamine has long been considered as a key intermediate of the Maillard reaction, which to a large extent is responsible for specific aroma, taste, and color formation in thermally processed or dehydrated foods. Since the 1980s, however, as a product of the Amadori rearrangement reaction between glucose and biologically significant amines such as proteins, fructosamine has experienced a boom in biomedical research, mainly due to its relevance to pathologies in diabetes and aging. In this chapter, we assess the scope of the knowledge on and applications of fructosamine-related molecules in chemistry, food, and health sciences, as reflected mostly in publications within the past decade. Methods of fructosamine synthesis and analysis, its chemical, and biological properties, and degradation reactions, together with fructosamine-modifying and -recognizing proteins are surveyed.

Development of glycated peptide enzyme sensor based flow injection analysis system for haemoglobin A1c monitoring using quasi-direct electron transfer type engineered fructosyl peptide oxidase

Haemoglobin A1c (hemoglobin A1c, HbA1c) is an important long-term glycemic control marker for diabetes. The aim of this study was to develop an enzyme flow injection analysis (FIA) system using engineered fructosyl peptide oxidase (FPOx) based on 2.5th generation principle for an HbA1c automated analytical system. FPOx from Phaeosphaeria nodorum (PnFPOx) was engineered by introducing a Lys residue at the R414 position, to be modified with amine reactive phenazine ethosulfate (arPES) in proximity of FAD. The engineered PnFPOx mutant with minimized oxidase activity, N56A/R414K, showed quasi-direct electron transfer (quasi-DET) ability after PES-modification. The FIA system was constructed by employing a PES-modified PnFPOx N56A/R414K and operated at 0 V against Ag/AgCl. The system showed reproducible responses with a linear range of 20-500 μM for both fructosyl valine (FV) and fructosyl valylhistidine (FVH), with sensitivities of 0.49 nA μM^-1 and 0.13 nA μM^-1, and the detection limits of 1.3 μM and 2.0 μM for FV and FVH, respectively. These results indicate that the enzyme electrochemical FIA system covers the clinical range of HbA1c detection for more 200 consecutive measurements. Protease digested three different levels of HbA1c samples including healthy and diabetic range subjects were also measured with the FIA system. Thus, it will be possible to develop an integrated system consisting of sample pretreatment and sample electrochemical measurement based on an FIA system possessing quasi-DET type PnFPOx.