Løvstad R A
Department of Medical Biochemistry, University of Oslo, Norway.
Biometals. 1997 Apr;10(2):123-6. doi: 10.1023/a:1018383207608.
The ferroxidase activity of ceruloplasmin is often determined according to the method of Johnson et al. (1967), using apotransferrin for trapping ferric ions generated by the enzyme; spectrophotometrically monitoring the Fe(3+)-transferrin formation at pH 6.0. Reports have shown that ascorbate inhibits this reaction, and it is hypothesized that the effect could be of physiological significance in individuals with a high ascorbate to ceruloplasmin ratio in plasma (e.g. premature babies). The present study shows that the inhibitory effect of ascorbate rapidly decreases with increasing pH. At pH 7.4 no significant effect was observed, the result suggesting that ascorbate is not a physiological inhibitor of ceruloplasmin. Furthermore, experiments demonstrate that at acidic pH the inhibitory effect of ascorbate on the rate of Fe(3+)-transferrin formation is not primarily due to an interaction with ceruloplasmin, but to a reduction of enzymically generated ferric ions before they are bound to apotransferrin.
铜蓝蛋白的铁氧化酶活性通常根据约翰逊等人（1967年）的方法测定，使用脱铁转铁蛋白捕获该酶产生的铁离子；在pH 6.0条件下，通过分光光度法监测Fe(3+)-转铁蛋白的形成。报告显示，抗坏血酸会抑制此反应，并且据推测，在血浆中抗坏血酸与铜蓝蛋白比例较高的个体（例如早产儿）中，这种效应可能具有生理意义。本研究表明，随着pH升高，抗坏血酸的抑制作用迅速降低。在pH 7.4时未观察到显著影响，该结果表明抗坏血酸不是铜蓝蛋白的生理抑制剂。此外，实验证明，在酸性pH条件下，抗坏血酸对Fe(3+)-转铁蛋白形成速率的抑制作用并非主要由于与铜蓝蛋白的相互作用，而是由于酶产生的铁离子在与脱铁转铁蛋白结合之前被还原。
