Effect of pH on the Optical Absorption Spectrum and Effective Number of the Bohr Magneton of Horse Erythrocyte Catalase in the Range from 77°K to 267°K
Effect of pH on the Optical Absorption Spectrum and Effective Number of the Bohr Magneton of Horse Erythrocyte Catalase in the Range from 77°K to 267°K
复制标题
pH值对马红细胞过氧化氢酶在77°K~267°K范围内的吸光光谱和有效玻尔磁子数的影响
DOI：
10.1093/oxfordjournals.jbchem.a129423
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发表时间：
1970
影响因子：
2.7
通讯作者：
Y. Ogura
中科院分区：
文献类型：
--
作者：
Koichi Yshida;T. Iizuka;Y. Ogura
在77°K至267°K的温度范围内，在不同pH值下，测定了马红细胞过氧化氢酶[EC 1.11.1.6]在冷冻状态下的光学吸收光谱。在pH 8.4和11.0的吸收光谱，这是主要的高自旋型在室温下，改变那些的混合型的高自旋和低自旋的形式冷却到液氮温度。另一方面，在pH 5.2下，在冷却至液氮温度时，光谱的高自旋型特征进一步增强。在77°K至267°K的温度下，在不同pH值下进行磁化率测量。当温度高于180°K时，有效玻尔磁子数（n2eff）的平方在酸性pH下减小，在碱性pH下增大。在酸性和碱性pH值下，n2eff值在180°K以下不受温度影响，在pH 5.0、9.8和10.3下分别为35、26.5和23.3。在液氮温度下测定了过氧化氢酶在不同pH值下的EPR吸收光谱。在酸性区域中，EPR光谱显示出g值为6.6和5.4的双峰信号和R值为2.03的弱信号。在碱性区，除了上述高自旋信号外，还出现了低自旋信号，其值分别为2.78，2.21和1.72.这些结果表明：（1）在酸性和碱性介质中，过氧化氢酶的血红素离子在低温下比在室温下分别表现出更多的高自旋和低自旋特征，（2）在180°K以下，酸性介质中的高铁血红素离子是纯的高自旋态，而碱性介质中的高铁血红素离子是高自旋态和低自旋态的混合物。有人认为过氧化氢酶中有两种形式的血红素，即酸性和碱性形式，其中H2分子和OH−离子分别与第六配位结合，并且酸性形式（Fe3+）H2O处于纯高自旋状态，而碱性形式（Fe3+）OH−在温度低于180°K时处于纯低自旋状态。
The optical absorption spectrum of horse erythrocyte catalase [EC 1.11.1.6] in the frozen state was measured at various pH-values at temperatures from 77°K to 267°K. The absorption spectra at pH 8.4 and 11.0, which were predominantly of a high-spin type at room temperature, changed to those of a mixed type of highspin and low-spin forms on cooling to liquid nitrogen temperature. At pH 5.2, on the other hand, the high-spin type character of the spectrum was further intensified on cooling to liquid nitrogen temperature. Magnetic susceptibility measurements were carried out at different pH-values at temperatures from 77°K to 267°K. The square of the effective Bohr magneton number (n2eff) decreased at a given acidic pH, and increased at a given alkaline pH, with the rise in temperature above 180°K. The values of n2eff were temperature independent below 180°K at acidic and alkaline pH-values, being 35, 26.5 and 23.3 at pH 5.0, 9.8 and 10.3, respectively. The EPR absorption spectra of catalase at different pH-values were measured at liquid nitrogen temperature. In the acidic region, the EPR spectrum exhibited a doublet signal with g-values of 6.6 and 5.4 and a weak signal with a Rvalue of 2.03. In the alkaline region, the spectrum exhibited low-spin type signals with values of 2.78, 2.21 and 1.72 in addition to the high-spin type signals described above.These results indicate that (1) the hematin irons of catalase in acidic and alkaline media show more high-spin and more low-spin character, respectively, at low temperatures than at room temperature, and (2) below 180°K the hematin irons in acidic medium are in a pure high-spin state, whereas those in alkaline medium are composed of a mixture of hematin irons in a high-spin state and in a low-spin state. It is considered that there are two forms of hematin in catalase,viz. acidic and alkaline forms, in which an H2molecule and an OH− ion, respectively, are bound to the sixth coordination position, and that the acidic form, (Fe3+)H2O, is in a purely high-spin state while the alkaline form, (Fe3+)OH−, is in a purely low-spin state at temperatures below 180°K.