Itoh S, Kusaka T, Imai T, Isobe K, Onishi S
Department of Pediatrics, Kagawa Medical University, Kitagun, Japan.
Ann Clin Biochem. 2000 Jul;37 ( Pt 4):452-6. doi: 10.1177/000456320003700404.
We examined the reactivity of human serum albumin-bound bilirubin and its photoisomers as substrates for a direct bilirubin assay using bilirubin oxidase. The reduction of (EZ)-cyclobilirubin reached 100% 5 min after addition of the enzyme at any pH tested (3.5-7.4) in 0.1 mol/L phosphate buffer, whereas the reduction of (ZE)-bilirubin or (ZZ)-bilirubin reached 100% only below pH 4.5 or 5.5, respectively. (ZZ)-Bilirubin and its photoisomers did not react in citrate-lactate buffer at pH 3.7. The circular dichroism spectrum of (ZZ)-bilirubin in this buffer did not show a positive Cotton effect. These results indicate that a three-dimensional structure surrounding the reaction site of bilirubin is important for the reactivity with bilirubin oxidase.
我们使用胆红素氧化酶，研究了人血清白蛋白结合胆红素及其光异构体作为直接胆红素测定底物的反应活性。在0.1 mol/L磷酸盐缓冲液中，于任何测试pH值（3.5 - 7.4）下加入该酶后5分钟，（EZ）-环胆红素的还原率达到100%，而（ZE）-胆红素或（ZZ）-胆红素的还原率分别仅在pH值低于4.5或5.5时达到100%。（ZZ）-胆红素及其光异构体在pH值为3.7的柠檬酸盐 - 乳酸盐缓冲液中不发生反应。该缓冲液中（ZZ）-胆红素的圆二色光谱未显示正科顿效应。这些结果表明，胆红素反应位点周围的三维结构对于与胆红素氧化酶的反应活性很重要。
