PROPERTIES OF CYTOCHROME-B5 AND METHEMOGLOBIN REDUCTION IN HUMAN-ERYTHROCYTES
PROPERTIES OF CYTOCHROME-B5 AND METHEMOGLOBIN REDUCTION IN HUMAN-ERYTHROCYTES
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DOI：
10.1111/j.1432-1033.1979.tb19735.x
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发表时间：
1979-01-01
期刊：
影响因子：
--
通讯作者：
SUGITA, Y
中科院分区：
文献类型：
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作者：
ABE, K;SUGITA, Y
人红细胞细胞色素b5的中点氧化还原电位为-2 mV，等电点为4.3，Km值为7微米。红细胞细胞色素b5为可溶性组分，相对分子质量小于肝细胞色素b5，与兔肝细胞色素b5相近。用改进的方法测定正常人红细胞中细胞色素b5的浓度，结果为0.22+-。获得0.02微米。人红细胞还原酶还原细胞色素b5的最适pH为5.5，在中性pH下约为最大酶活的一半。作为电子供体，α-NADH和NADPH的效率分别为β-NADH的56%和1%。用荧光法测得β-NADH的Km为22 nm。利用体内底物浓度计算出正常人红细胞细胞色素b5还原速率为1.4 mm/h。测定了细胞色素b5还原高铁血红蛋白的速率常数为6.2倍。103M-1 S-1。这些值解释了之前提出的假设(Hultquist，Sugita)下的高铁血红蛋白还原速率，即高铁血红蛋白被细胞色素b5非酶还原，细胞色素b5被NADH-toChrome b5还原酶还原。
Cytochrome b5 of human erythrocytes showed a midpoint redox potential of -2 mV, and isoelectric point of 4.3 and a Km of 7 .mu.M for erythrocyte cytochrome b5 reductase. These values were close to those of rabbit liver cytochrome b5, though cytochrome b5 of erythrocytes is in the soluble fraction and its relative molecular mass was smaller than that of liver cytochrome b5. The concentration of cytochrome b5 in normal human erythrocytes was determined by an improved method and a value of 0.22 .+-. 0.02 .mu.M was obtained. The optimum pH of the cytochrome b5 reduction by the reductase from human erythrocytes was 5.5, and about half of the maximum activity was observed at neutral pH. As electron donors, .alpha.-NADH and NADPH were 56% and 1% as effective as .beta.-NADH, respectively. A Km of 22 nM for .beta.-NADH was obtained by fluorometric assay method. The rate of cytochrome b5 reduction in normal human erythrocytes was calculated to be 1.4 mM/h by the use of substrate concentrations in vivo. The rate constant of the nonenzymatic methemoglobin reduction by reduced cytochrome b5 was determined to be 6.2 .times. 103 M-1 S-1. These values account for the methemoglobin reduction rate in human erythrocytes on the hypothesis proposed previously (Hultquist, Sugita), i.e, methemoglobin is reduced nonenzymatically by cytochrome b5 which was reduced by NADH-tochrome b5 reductase.