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外文期刊>The biochemical journal
>Thermal inactivation studies of normal and variant human erythrocyte carbonic anhydrases by using a sulphonamide-binding assay
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Thermal inactivation studies of normal and variant human erythrocyte carbonic anhydrases by using a sulphonamide-binding assay
pHeat-inactivation studies were carried out on the two primary erythrocyte carbonic anhydrase isoenzymes, CA I and CA II, and the secondary isoenzyme of CA I, CA I (+1). In addition, two genetic variants of human isoenzyme CA I, CA Id Michigan (100 Thr→Lys) and CA If London (102 Glu →Lys), and one variant of isoenzyme CA II, CA IIh (251 Asn→Asp), were similarly analysed. The first-order rate constants and Arrhenius plots for these six enzyme forms showed that (1) isoenzyme CA II is more heat-stable than CA I, (2) isoenzyme CA I (+1) is less heat-stable than CA I, (3) the variants CA IIh and CA If London are less heat-stable than the normal enzymes, and (4) isoenzyme CA Id Michigan is more heat-stable than normal CA I. From the values of the slopes of the Arrhenius plots, the energy of activation (iE/isuba/sub) for each isoenzyme and isoenzyme variant was determined, and the following thermodynamic activation parameters were calculated at 55°C: the free energy of activation (ΔiG/isup?/sup), the activation enthalpy (ΔiH/isup?/sup) and the activation entropy (ΔiS/isup?/sup). The ΔiG/isup?/sup for the enzymes shows a relative constancy with compensating variation in ΔiH/isup?/sup and ΔiS/isup?/sup. When the values for ΔiH/isup?/sup are plotted against ΔiS/isup?/sup, an increase in ΔiH/isup?/sup involves a concomitant increase in ΔiS/isup?/sup./p
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机译:对两种主要的红细胞碳酸酐酶同工酶CA I和CA II以及次要的CA I CA I(+1)同工酶进行了热失活研究。此外,还有人同工酶CA I,CA Id密歇根州(100 Thr→Lys)和CA If London(102 Glu→Lys)的两个遗传变异体和同工酶CA II,CA IIh(251 Asn→Asp)的同工酶变异体。类似地进行了分析。这六种酶形式的一级速率常数和Arrhenius图表明(1)同功酶CA II比CA I更热稳定;(2)同功酶CA I(+1)比CA I更不耐热; (3)变体CA IIh和CA如果伦敦的热稳定性低于正常酶,并且(4)同功酶CA Id密歇根州的耐热性高于正常CAI。从阿伦尼乌斯曲线的斜率值可以看出,确定每种同功酶和同功酶变体的激活能( E i> a sub>),并在55°C下计算以下热力学激活参数:激活的自由能( Δ G i> ? sup>),激活焓(Δ H i> ? sup>)和激活熵(Δ S i> ? sup>)。酶的Δ G i> ? sup>显示相对恒定性,且Δ H i> ? sup>和Δ S i> ? sup>。当将Δ H i> ? sup>的值相对于Δ S i> ? sup>绘制时,Δ H的增加 i> ? sup>伴随Δ S i> ? sup>的增加。 p>
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