RESONANCE RAMAN EVIDENCE FOR OXYGEN-EXCHANGE BETWEEN THE FE-IV=O HEME AND BULK WATER DURING ENZYMATIC CATALYSIS OF HORSERADISH-PEROXIDASE AND ITS RELATION WITH THE HEME-LINKED IONIZATION
RESONANCE RAMAN EVIDENCE FOR OXYGEN-EXCHANGE BETWEEN THE FE-IV=O HEME AND BULK WATER DURING ENZYMATIC CATALYSIS OF HORSERADISH-PEROXIDASE AND ITS RELATION WITH THE HEME-LINKED IONIZATION
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DOI：
10.1073/pnas.83.8.2417
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发表时间：
1986-04-01
影响因子：
11.1
通讯作者：
KITAGAWA, T
中科院分区：
文献类型：
--
作者：
HASHIMOTO, S;TATSUNO, Y;KITAGAWA, T
辣根过氧化物酶的化合物II的拉曼光谱研究表明，血红素的FeIV oxene配体中的氧原子在pH 7.0的H2O中迅速交换，但在碱性溶液（pH 11.0）中不交换。这一结论是基于在H2 18 O中化合物II的FeIV oxene配体拉伸模式的移位的研究;进一步的研究表明，FeIV oxene配体血红素在中性溶液中与蛋白质的氨基酸残基氢键结合，但在碱性溶液中不与蛋白质的氨基酸残基氢键结合。该残基的去质子化在中点pH为8.8时发生，因此对应于所谓的血红素连接的电离。它的结论是，这个氢键质子在氧交换机制中起着重要的作用。由此看来，很明显，该氢键质子在该酶的酸/碱催化中具有重要作用，并且该酶的碱性失活可归因于在高pH下缺乏氢键质子。
Raman spectroscopic studies of compound II of horseradish peroxidase show that the oxygen atom in the FeIV oxene ligand of the heme is rapidly exchanged in H2O at pH 7.0 but not in an alkaline solution (pH 11.0). This conclusion is based on studies of shift in the FeIV oxene ligand stretching mode of compound II in H2 18O; further studies show that the FeIV oxene ligand heme is hydrogen-bonded to an amino acid residue of the protein in neutral solutions but not in the alkaline solution. Deprotonation of this residue takes place with the midpoint pH at 8.8 and accordingly corresponds to the so-called heme-linked ionization. It is concluded that this hydrogen-bonded proton plays an important part in the oxygen exchange mechanism. From this it seems clear that this hydrogen-bonded proton has an essential role in the acid/base catalysis of this enzyme and that alkaline deactivation of this enzyme can be attributed to the lack of a hydrogen-bonded proton at high pH.