Resonance Raman spectra of protocatechuate 3,4-dioxygenase. Evidence for coordination of tyrosine residue to ferric iron
Resonance Raman spectra of protocatechuate 3,4-dioxygenase. Evidence for coordination of tyrosine residue to ferric iron
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原儿茶酸 3,4-双加氧酶的共振拉曼光谱。
DOI：
10.1021/ja00482a059
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发表时间：
1978
影响因子：
15
通讯作者：
S. Otsuka
中科院分区：
文献类型：
--
作者：
Y. Tatsuno;Y. Saeki;M. Iwaki;T. Yagi;M. Nozaki;T. Kitagawa;S. Otsuka
HOOC-^OH U2 HOOC-^b-COOH每个分子有8个铁原子(摩尔重量700 000)，由8个相同的原基组成，每个原基由两对不同的亚基(^？)组成·2酶呈红色，在450 nm附近有广泛的吸收，这归因于铁与多肽链上的一些氨基酸残基配位(见图1的插图)。当底物(原儿茶酸)无序加入时，可见光谱的强度增加了~480 nm，表明形成了酶-底物(ES)复合体。当进入氧气时，在520 nm处出现新的吸收，这表明形成了一个三元络合物(ESOI)。当底物被消耗时，原始光谱被恢复。3铁原子显然在氧和/或底物的活化中起着重要作用。因此，阐明铁周围的配位环境对于了解酶反应的机理是非常重要的。一份先前的报告提出，在EPR谱的基础上，四个半胱氨基硫原子的四面体排列类似于Rubredosin的情况，4而另一份基于穆斯堡尔谱的研究表明，氧或氮，而不是硫，与铁配位。5他们的结论彼此不一致。作为共振拉曼散射
HOOC-^ OH U2 HOOC-^ b-COOH eight atoms of ferric iron per molecule (mol wt 700 000) and consists of eight identical protomers, each of which is composed of two pairs of nonidentical subunits (^ ß)· 2 The enzyme shows a red color with a broad absorption near 450 nm which is attributable to the ferric iron coordinated with some amino acid residues of the polypeptide chains (see the inset of Figure 1). When the substrate (protocatechuic acid) is added anaer-obically, the visible spectrum shows an increase in intensity of~ 480 nm implying the formation of an enzyme-substrate (ES) complex. Upon admission of oxygen a new absorption arises at 520 nm, suggestive of the formation of a ternary complex (ESOi). When the substrate is consumed, the original spectrum is recovered. 3 Apparently the iron atoms play an important role in the activation of oxygen and/or substrate. Elucidation of the coordination environment around the ferric iron is thus of primary importance for understanding the mechanism of the enzymic reaction. A previous report suggested, on the basis of EPR spectroscopy, a tetrahedral ar-rangement of four cysteinyl sulfur atoms similar to the case of rubredoxin, 4 while another study based on Móssbauer spectrum claimed coordination of oxygen or nitrogen, but not sulfur, to the ferric iron. 5 Thustheir conclusions are in-consistent with each other. As the resonance Raman scattering