Models for coordination site of cytochrome P-450, characterization of hemin-thiolato complexes with S, O, and N donor ligands by electronic absorption and electron spin resonance spectra |
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Authors: | H Sakurai T Yoshimura |
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Institution: | Faculty of Pharmaceutical Sciences, University of Tokushima, Japan;The Environmental Science Institute of Hyogo Prefecture, Kobe, Japan |
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Abstract: | Bisthiolato-hemin complexes exhibiting "two split Soret bands" at 370 and 460 nm, classified into "hyperporphyrin spectrum" was prepared with naturally occurring porphyrins (Fe(III)protoporphyrin IX and its dimethyl ester), thioglycolate esters, and tetramethylammonium hydroxide in organic solvents. The structure of the complexes was characterized by electronic absorption and electron spin resonance (ESR) spectrometries. These complexes were stable under air at room temperature, their apparent half-lives being about 30 min monitored by the intensities of the two Soret bands. Thus the bisthiolato-hemin complex containing thioglycolate ester was shown to be a model for the cytochrome P450(P450)-thiolato binding complex. Ligand exchange reactions of the bisthiolato-hemin complex with imidazole or methanol indicated that the intermediate species are stabilized as thiolato-hemin-imidazole or -methanol complexes. The latter intermediate complex was suggested to be a good model for low-spin ferric P450 as characterized by distinct beta- and alpha-bands at 530 and 560 nm, respectively, as well as a single Soret peak at approximately 410 nm. The result of the analysis on ESR g values and crystal field parameters for the bisthiolato-hemin, thiolato-hemin-imidazole, and thiolato-hemin-oxygen ligand complexes comparing with those for P450 itself and the ligand binding complexes revealed that the sixth ligand trans to the fifth thiolato ligand of the low-spin ferric P450 can be an oxygen atom of water molecule. |
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Keywords: | HPS hyperporphyrin spectrum (or spectra) ESR electron spin resonance PPIX protoporphyrin IX PPIXDME PPIX dimethyl ester P450 cytochrome P-450 Hb hemoglobin Mb myoglobin TGE thioglycolate ethyl ester TGHE thioglycolate ethyl hexyl ester TGOD thioglycolate octadecyl ester TN thionalide MAA mercaptoacetanilide φ-SH thiophenol 4-nitro-thiophenol ME mercaptoethanol DTT dithiothreitol Cys cysteine Py pyndine Im imidazole 2MeIm 2-methyl-Im 4MeIm 4-methyl-Im 2EtIm 2-ethyl-Im MeOH methanol EtOH ethanol Oc-S-Me octyl-methyl-sulfide DMF dimethylformamide DMSO dimethyl sulfoxide |
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