Washburn M P, Wells W W
Department of Biochemistry, Michigan State University, East Lansing 48824, USA.
Free Radic Biol Med. 1997;23(4):563-70. doi: 10.1016/s0891-5849(97)00001-4.
Recombinant pig liver thioltransferase (rPLTT) catalyzes the reduction of alloxan to dialuric acid by glutathione (GSH). This is the second non-disulfide substrate, after dehydroascorbic acid, described for thioltransferase. The reaction kinetics, measured by a coupled assay including glutathione disulfide reductase and NADPH yielded a Km = 82 microM for alloxan, a k(cat) = 37 s(-1), and a k(cat)/Km = 4.5 x 10(5) M(-1) s(-1). The presence of rPLTT suppressed the competitive formation of compound 305, an alloxan-GSH conjugate of unknown structure, and at GSH concentrations between 0.05 mM and 1.5 mM, oxygen consumption was greater than that recorded in the uncatalyzed reaction. Both superoxide dismutase and catalase inhibited oxygen consumption in 1.0 mM GSH and 0.2 mM alloxan in the presence of rPLTT. This study suggests that thioltransferase (glutaredoxin) plays a significant role in the cytotoxicity of alloxan in vulnerable tissues.
重组猪肝硫醇转移酶（rPLTT）催化谷胱甘肽（GSH）将四氧嘧啶还原为二脲酸。这是继脱氢抗坏血酸之后，硫醇转移酶所作用的第二种非二硫键底物。通过包括谷胱甘肽二硫化物还原酶和NADPH的偶联测定法测得的反应动力学结果显示，四氧嘧啶的Km值为82微摩尔，k(cat)为37秒⁻¹，k(cat)/Km为4.5×10⁵M⁻¹秒⁻¹。rPLTT的存在抑制了化合物305（一种结构未知的四氧嘧啶 - GSH共轭物）的竞争性形成，并且在GSH浓度介于0.05毫摩尔和1.5毫摩尔之间时，耗氧量大于未催化反应中的记录值。在rPLTT存在的情况下，超氧化物歧化酶和过氧化氢酶均抑制了1.0毫摩尔GSH和0.2毫摩尔四氧嘧啶体系中的耗氧量。这项研究表明硫醇转移酶（谷氧还蛋白）在四氧嘧啶对脆弱组织的细胞毒性中起重要作用。
