Baker J R, Zyzak D V, Thorpe S R, Baynes J W
Department of Clinical Biochemistry, Green Lane Hospital, Auckland, New Zealand.
Clin Chem. 1994 Oct;40(10):1950-5.
The chemistry of the fructosamine assay was studied by using the Amadori compound, N alpha-formyl-N epsilon-fructose-lysine (fFL), an analog of glycated lysine residues in protein. Previously (Clin Chem 1993;39:2460-5), we reported that free lysine was formed from fFL at 70% yield during incubation with alkaline nitroblue tetrazolium (NBT) under the conditions routinely used for the fructosamine assay (sodium carbonate buffer, pH 10.35 at 37 degrees C). Here, we show that D-glucosone is the primary carbohydrate oxidation product formed from Amadori compounds in the fructosamine assay. Glucosone, which decomposes under alkaline assay conditions with a half-life of < 30 min, reaches a maximum concentration of approximately 50% of the initial fFL concentration after 10 min of incubation. Like fFL, glucosone reduces NBT to the purple monoformazan dye, but its decomposition is not accelerated by the presence of NBT. The dicarbonyl-trapping reagent, aminoguanidine, inhibits the fructosamine assay by approximately 25% when fFL is the substrate, but by nearly 100% with glucosone as substrate. Studies with serum samples from diabetics and nondiabetics indicate that glucosone formation does not have a significant effect on the clinical usefulness of the fructosamine assay; however, corrections for glucosone formation may be required when the assay is used for estimating the extent of glycation of proteins.
通过使用Amadori化合物Nα-甲酰基-Nε-果糖赖氨酸（fFL）（一种蛋白质中糖化赖氨酸残基的类似物）对果糖胺测定的化学过程进行了研究。此前（《临床化学》1993年；39:2460 - 5），我们报道在果糖胺测定常规使用的条件下（碳酸钠缓冲液，37℃时pH 10.35），fFL与碱性硝基蓝四氮唑（NBT）孵育期间，游离赖氨酸以70%的产率从fFL中生成。在此，我们表明D - 葡糖酮是果糖胺测定中由Amadori化合物形成的主要碳水化合物氧化产物。葡糖酮在碱性测定条件下分解，半衰期<30分钟，孵育10分钟后达到的最大浓度约为初始fFL浓度的50%。与fFL一样，葡糖酮将NBT还原为紫色的单甲臜染料，但其分解不会因NBT的存在而加速。二羰基捕获试剂氨基胍，当以fFL为底物时，对果糖胺测定的抑制约为25%，但以葡糖酮为底物时抑制近100%。对糖尿病患者和非糖尿病患者血清样本的研究表明，葡糖酮的形成对果糖胺测定的临床实用性没有显著影响；然而，当该测定用于估计蛋白质糖化程度时，可能需要对葡糖酮的形成进行校正。
