Karra Sushma, Griffith Wendell P, Kennedy Robert T, Gorski Waldemar
Department of Chemistry, University of Texas at San Antonio, San Antonio, TX 78249-0698, USA.
Analyst. 2016 Apr 21;141(8):2405-11. doi: 10.1039/c5an02636a. Epub 2016 Mar 3.
The oxidation of glucagon, which is one of the key hormones in glucose homeostasis, was studied at electrodes modified with carbon nanotubes (CNT) that were dispersed in a polysaccharide adhesive chitosan (CHIT). Such electrodes displayed improved resistance to fouling, which allowed for the investigation of both the electrolysis/mass spectrometry and electroanalysis of glucagon. The off-line electrospray ionization and tandem mass spectrometric analyses showed that the -4 Da mass change to glucagon upon electrolysis at CNT was due to the electrooxidation of its tryptophan (W25) and dityrosine (Y10, Y13) residues. The methionine residue of glucagon did not contribute to its oxidation. The amperometric determination of glucagon yielded the limit of detection equal to ∼20 nM (E = 0.800 V, pH 7.40, S/N = 3), sensitivity of 0.46 A M(-1) cm(-2), linear dynamic range up to 2.0 μM (R(2) = 0.998), response time <5 s, and good signal stability. Free tryptophan and tyrosine yielded comparable analytical figures of merit. The direct amperometric determination of unlabeled glucagon at CHIT-CNT electrodes is the first example of a rapid alternative to the complex analytical assays of this peptide.
胰高血糖素是葡萄糖稳态中的关键激素之一，对其在分散于多糖粘合剂壳聚糖（CHIT）中的碳纳米管（CNT）修饰电极上的氧化过程进行了研究。此类电极表现出更好的抗污染能力，这使得对胰高血糖素的电解/质谱分析和电分析成为可能。离线电喷雾电离和串联质谱分析表明，在CNT上进行电解时，胰高血糖素质量减少4 Da是由于其色氨酸（W25）和二酪氨酸（Y10、Y13）残基的电氧化。胰高血糖素的甲硫氨酸残基对其氧化没有贡献。胰高血糖素的安培测定法得到的检测限约为20 nM（E = 0.800 V，pH 7.40，S/N = 3），灵敏度为0.46 A M(-1) cm(-2)，线性动态范围高达2.0 μM（R(2) = 0.998），响应时间<5 s，且信号稳定性良好。游离色氨酸和酪氨酸给出了类似的分析性能指标。在CHIT-CNT电极上直接安培测定未标记的胰高血糖素首次为这种肽的复杂分析方法提供了一种快速替代方案。
