McGregor S J, Brock J H
University Department of Immunology, Western Infirmary, Glasgow, Scotland, UK.
Clin Chem. 1992 Sep;38(9):1883-5.
Although both Al and Fe are bound to transferrin in plasma, they are metabolized differently. Aluminum is less tightly bound to transferrin than is Fe, and might be released in circumstances in which Fe remains bound. The effect of pH ana citrate on the binding of 67Ga (a radiotracer used as an analog of Al) to transferrin in normal human serum was tested in the presence of physiological concentrations of CO2. At pH less than 6.8, Ga started to dissociate from transferrin; at pH 6, greater than 50% of the added 67Ga was present in a low-M(r) form. In contrast, almost all Fe remained bound to transferrin at pH values as low as 4.7. Citrate at concentrations as great as 100 mmol/L had no effect on binding of Fe, but the binding of 67Ga was markedly reduced at citrate greater than 1 mmol/L. Being bound to transferrin less strongly than Ga is, Al could dissociate even more readily, and loss of Al from transferrin in the kidney might explain why Al but not Fe is excreted in urine.
虽然铝（Al）和铁（Fe）在血浆中均与转铁蛋白结合，但它们的代谢方式不同。铝与转铁蛋白的结合不如铁紧密，在铁仍保持结合的情况下铝可能会被释放出来。在生理浓度的二氧化碳存在下，测试了pH值和柠檬酸盐对67Ga（一种用作铝类似物的放射性示踪剂）与正常人血清中转铁蛋白结合的影响。在pH值小于6.8时，镓开始从转铁蛋白上解离；在pH值为6时，添加的67Ga中超过50%以低分子量形式存在。相比之下，在低至4.7的pH值下，几乎所有的铁仍与转铁蛋白结合。浓度高达100 mmol/L的柠檬酸盐对铁的结合没有影响，但当柠檬酸盐浓度大于1 mmol/L时，67Ga的结合明显减少。由于铝与转铁蛋白的结合比镓更弱，铝可能更容易解离，肾脏中转铁蛋白上铝的丢失可能解释了为什么铝而不是铁会随尿液排出。
