AB-INITIO QUANTUM-CHEMICAL STUDY OF THE COBALT D-D SPECTROSCOPY OF SEVERAL SUBSTITUTED ZINC ENZYMES
AB-INITIO QUANTUM-CHEMICAL STUDY OF THE COBALT D-D SPECTROSCOPY OF SEVERAL SUBSTITUTED ZINC ENZYMES
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DOI：
10.1021/ja00075a046
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发表时间：
1993-11-03
影响因子：
15
通讯作者：
KRAUSS, M
中科院分区：
文献类型：
--
作者：
GARMER, DR;KRAUSS, M
The visible spectroscopy of cobalt-substituted zinc enzymes provides insight into the electronic and structural environment of the active site. Ab initio calculations of the d-d spectra of model complexes of cobalt are applied to an analysis of the following enzymes: liver alcohol dehydrogenase (LADH), carboxypeptidase A (CPA), thermolysin (TLN), and carbonic anhydrase (CA). For the well-characterized active site of the LADH resting state, the calculated spectra agrees well with experiment both in the infrared and visible. The spectra in the presence of metal-bound deprotonated water or alcohol is predicted and can be used to characterize this stage of the reaction mechanism. Similarities in the active sites and resulting spectra of CPA and TLN are examined with models that explore the rotational flexibility of ligands implied by experimental differences in crystal and solution structures. Insight into the mechanism of anion inhibitor binding is obtained by comparing the spectra of CA with thiocyanate and cyanate. Experimental and theoretical spectra are in good agreement for thiocyanate, but the theoretical cyanate spectra does not fit experiment. The spectra is found to resemble more closely the high pH form of the uninhibited CA which is in accord with the recent X-ray crystallographic observation that the cyanate binds in the second shell of the zinc active site. However, the present suggestion that the water bound to the cobalt is deprotonated leads to a different interpretation of the mechanism of binding of inhibitors like cyanate than proposed earlier. Although the cyanate in the second shell has a small effect on the d-d spectra of cobalt, the deprotonated water suggests that desolvated cyanate abstracts the
