二价阳离子对NADH：细胞色素b5还原酶和NADPH：细胞色素c还原酶还原细胞色素b5的相反作用。
The opposite effect of bivalent cations on cytochrome b5 reduction by NADH:cytochrome b5 reductase and NADPH:cytochrome c reductase.
作者信息
Tamura M, Yubisui T, Takeshita M
机构信息
Department of Biochemistry, Oita Medical College, Japan.
出版信息
Biochem J. 1988 May 1;251(3):711-5. doi: 10.1042/bj2510711.
The effects of bivalent cations on cytochrome b5 reduction by NADH:cytochrome b5 reductase and NADPH:cytochrome c reductase were studied with the proteinase-solubilized enzymes. Cytochrome b5 reduction by NADH:cytochrome b5 reductase was strongly inhibited by CaCl2 or MgCl2. When 1.2 microM-cytochrome b5 was used, the concentrations of CaCl2 and MgCl2 required for 50% inhibition (I50) were 8 and 18 mM respectively. The inhibition was competitive with respect to cytochrome b5. The extent of inhibition by CaCl2 or MgCl2 was much higher than that by KCl or other alkali halides. In contrast, cytochrome b5 reduction by NADPH:cytochrome c reductase was extremely activated by CaCl2 or MgCl2. In the presence of 5 mM-CaCl2, the activity was 24-fold higher than control when 4.4 microM-cytochrome b5 was used. The magnitude of activation by CaCl2 was 2-3-fold higher than that by MgCl2. The activation by these salts was much higher than that by KCl, indicating that bivalent cations play an important role in this activation. The mechanisms of inhibition and activation by bivalent cations of cytochrome b5 reduction by these two microsomal reductases are discussed.
利用蛋白酶增溶的酶研究了二价阳离子对NADH：细胞色素b5还原酶和NADPH：细胞色素c还原酶还原细胞色素b5的影响。NADH：细胞色素b5还原酶还原细胞色素b5的过程受到CaCl2或MgCl2的强烈抑制。当使用1.2微摩尔的细胞色素b5时，50%抑制率（I50）所需的CaCl2和MgCl2浓度分别为8毫摩尔和18毫摩尔。这种抑制作用相对于细胞色素b5具有竞争性。CaCl2或MgCl2的抑制程度远高于KCl或其他碱金属卤化物。相反，NADPH：细胞色素c还原酶还原细胞色素b5的过程受到CaCl2或MgCl2的极大激活。在存在5毫摩尔CaCl2的情况下，当使用4.4微摩尔细胞色素b5时，活性比对照高24倍。CaCl2的激活幅度比MgCl2高2至3倍。这些盐类的激活作用远高于KCl，表明二价阳离子在这种激活中起重要作用。本文讨论了这两种微粒体还原酶中二价阳离子对细胞色素b5还原的抑制和激活机制。
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