Alternative modes of substrate distortion in enzyme and antibody catalyzed ferrochelation reactions
Alternative modes of substrate distortion in enzyme and antibody catalyzed ferrochelation reactions
复制标题
DOI：
10.1021/bi972616f
复制
发表时间：
1998-01-20
期刊：
影响因子：
2.9
通讯作者：
Spiro, TG
中科院分区：
文献类型：
--
作者：
Blackwood, ME;Rush, TS;Spiro, TG
共振拉曼光谱显示，催化金属插入卟啉的抗体和相应的酶亚铁螯合酶都会引起结合的卟啉底物的变形。发现酶引起的变形与抗体引起的变形不同；催化抗体产生与半抗原 N-甲基中卟啉 IX (N-MeMP) 中存在的变形相似的变形。特定面外振动模式的激活表明，抗体诱导吡咯环交替上下倾斜，而亚铁螯合酶诱导所有四个吡咯环朝同一方向倾斜（隆起）。这两种变形都能有效地催化金属插入。仅当抑制性金属离子也被结合时，酶中引起的变形才会出现。这一观察结果表明了一种变构机制，其中相邻位点的金属结合诱导了使卟啉向过渡态几何形状扭曲的构象变化。相反，该抗体不具有金属结合位点，并且似乎主要通过与卟啉的结合相互作用发挥作用。
Both an antibody that catalyzes metal insertion into porphyrins and the corresponding enzyme, ferrochelatase, are shown by resonance Raman spectroscopy to induce distortion in the bound porphyrin substrate. It was found that the enzyme-induced distortion is different from that induced by the antibody; the catalytic antibody produces a distortion which is similar to the one present in the hapten, N-methylmesoporphyrin IX (N-MeMP). Activation of specific out-of-plane vibrational modes reveal that the antibody induces an alternating up-and-down tilting of the pyrrole rings, while ferrochelatase induces tilting of all four pyrrole rings in the same direction (doming). Both distortions are effective in catalyzing metal insertion. The distortion induced in the enzyme is only seen when an inhibitory metal ion is also bound. This observation suggests an allosteric mechanism, in which a conformational change which distorts the porphyrin toward the transition state geometry, is induced by metal binding at an adjacent site. In contrast, the antibody does not have a metal binding site and appears to function largely through binding interactions with the porphyrin.