Nineteen fluorescent pH standards or pI markers ranging pH 3.64−10.12 were developed for use in capillary isoelectric focusing using laser-induced fluorescence detection. Tetra- to tridecapeptides containing one cysteine residue were designed to focus sharply at their respective isoelectric points by including amino acids that contain charged side chains, the pKa values of which are close to the corresponding pI values. An iodoacetylated derivative of tetramethylrhodamine was coupled to the thiol group of cysteine to yield fluorescent pI markers. The pI values of the labeled peptides were precisely determined after isoelectric focusing on polyacrylamide gel slabs by direct measurement of the pH of the focused bands. The markers were subjected to capillary isoelectric focusing for 10−15 min in coated capillaries under conditions of low electroosmosis and were detected by means of a scanning laser-induced fluorescence detector down to a level of subpicomolar range. The markers permitted the calibration of a wide-range pH gradient formed in a capillary by fluorescence detection for the first time and should facilitate the development of highly sensitive analytical methods based on a combination of capillary isoelectric focusing and laser-induced fluorescence detection.
利用激光诱导荧光检测技术开发了 19 种荧光 pH 标准或 pI 标记,pH 值范围为 3.64-10.12,用于毛细管等电点聚焦。含有一个半胱氨酸残基的四至十三肽被设计成能在各自的等电点上聚焦,方法是加入含有带电侧链的氨基酸,这些侧链的 pKa 值接近相应的 pI 值。四甲基罗丹明的碘乙酰化衍生物与半胱氨酸的硫醇基偶联,产生荧光 pI 标记。在聚丙烯酰胺凝胶板上进行等电聚焦后,通过直接测量聚焦条带的 pH 值,可精确测定标记肽的 pI 值。在低电渗条件下,标记物在有涂层的毛细管中进行 10-15 分钟的毛细管等电聚焦,并通过扫描激光诱导荧光检测器检测到亚皮摩尔范围的标记物。这些标记物首次允许通过荧光检测对毛细管中形成的宽范围 pH 梯度进行校准,并有助于开发基于毛细管等电聚焦和激光诱导荧光检测相结合的高灵敏度分析方法。