Pond A E, Roach M P, Sono M, Rux A H, Franzen S, Hu R, Thomas M R, Wilks A, Dou Y, Ikeda-Saito M, Ortiz de Montellano P R, Woodruff W H, Boxer S G, Dawson J H
Department of Chemistry and Biochemistry, University of South Carolina, Columbia 29208, USA.
Biochemistry. 1999 Jun 8;38(23):7601-8. doi: 10.1021/bi9825448.
UV-visible absorption and magnetic circular dichroism (MCD) data are reported for the cavity mutants of sperm whale H93G myoglobin and human H25A heme oxygenase in their ferric states at 4 degreesC. Detailed spectral analyses of H93G myoglobin reveal that its heme coordination structure has a single water ligand at pH 5.0, a single hydroxide ligand at pH 10.0, and a mixture of species at pH 7.0 including five-coordinate hydroxide-bound, and six-coordinate structures. The five-coordinate aquo structure at pH 5 is supported by spectral similarity to acidic horseradish peroxidase (pH 3.1), whose MCD data are reported herein for the first time, and acidic myoglobin (pH 3.4), whose structures have been previously assigned by resonance Raman spectroscopy. The five-coordinate hydroxide structure at pH 10.0 is supported by MCD and resonance Raman data obtained here and by comparison with those of other known five-coordinate oxygen donor complexes. In particular, the MCD spectrum of alkaline ferric H93G myoglobin is strikingly similar to that of ferric tyrosinate-ligated human H93Y myoglobin, whose MCD data are reported herein for the first time, and that of the methoxide adduct of ferric protoporphyrin IX dimethyl ester (FeIIIPPIXDME). Analysis of the spectral data for ferric H25A heme oxygenase at neutral pH in the context of the spectra of other five-coordinate ferric heme complexes with proximal oxygen donor ligands, in particular the p-nitrophenolate and acetate adducts of FeIIIPPIXDME, is most consistent with ligation by a carboxylate group of a nearby glutamyl (or aspartic) acid residue.
报道了抹香鲸H93G肌红蛋白和人H25A血红素加氧酶的腔突变体在4℃铁状态下的紫外可见吸收和磁圆二色性（MCD）数据。对H93G肌红蛋白的详细光谱分析表明，其血红素配位结构在pH 5.0时具有单个水配体，在pH 10.0时具有单个氢氧根配体，在pH 7.0时具有多种物种的混合物，包括五配位氢氧根结合结构和六配位结构。pH 5时的五配位水合结构通过与酸性辣根过氧化物酶（pH 3.1）的光谱相似性得到支持，本文首次报道了其MCD数据，以及酸性肌红蛋白（pH 3.4），其结构先前已通过共振拉曼光谱确定。pH 10.0时的五配位氢氧根结构通过此处获得的MCD和共振拉曼数据以及与其他已知五配位氧供体配合物的数据比较得到支持。特别是，碱性铁H93G肌红蛋白的MCD光谱与铁酪氨酸连接的人H93Y肌红蛋白（本文首次报道其MCD数据）以及铁原卟啉IX二甲酯（FeIIIPPIXDME）的甲醇加合物的MCD光谱惊人地相似。在其他具有近端氧供体配体的五配位铁血红素配合物的光谱背景下，特别是FeIIIPPIXDME的对硝基苯酚盐和乙酸盐加合物，对中性pH下铁H25A血红素加氧酶的光谱数据进行分析，最符合附近谷氨酰基（或天冬氨酸）残基的羧基进行配位的情况。
