Alternative modes of substrate distortion in enzyme and antibody catalyzed ferrochelation reactions

被引:65
作者
Blackwood, ME
Rush, TS
Romesberg, F
Schultz, PG
Spiro, TG [1 ]
机构
[1] Princeton Univ, Dept Chem, Princeton, NJ 08544 USA
[2] Univ Calif Berkeley, Howard Hughes Med Inst, Dept Chem, Berkeley, CA 94720 USA
关键词
D O I
10.1021/bi972616f
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
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.
引用
收藏
页码:779 / 782
页数:4
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