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首页> 外文期刊>Biochemistry >Steady-State Kinetics of Phytoglobin-Catalyzed Reduction of Hydroxylamine to Ammonium
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Steady-State Kinetics of Phytoglobin-Catalyzed Reduction of Hydroxylamine to Ammonium

机译：植物植物催化减少羟胺至铵的稳态动力学

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摘要

Phytoglobins are plant hexacoordinate hemoglobins with reversible coordination of a histidine side chain to the ligand binding site of the heme iron. They mediate electron transfer reactions such as nitric oxide scavenging and are particularly efficient at reducing nitrite and hydroxylamine. Previous work with phytoglobins has focused only on single turnovers of these reactions and has not revealed whether structural features, such as histidine hexacoordination, play a prominent role in the complete catalytic cycle. This work characterizes steady-state phytoglobin catalysis of reduction of hydroxylamine to ammonium using two different chemical reductants. K-m and k(cat) values were measured for rice phytoglobin, horse myoglobin, human neuroglobin, and a rice phytoglobin mutant protein in which the hexacoordinating histidine has been replaced with leucine (Phyt:H73L). The results demonstrate that phytoglobin catalysis driven by benzyl viologen is limited only by the dissociation rate constant for the distal histidine. This is consistent with the rate limit in single-turnover experiments and demonstrates that the kinetics of hydroxylamine binding, and not phytoglobin reduction, ultimately governs the reaction. Catalysis by the other proteins that either lack or have tighter hexacoordination is much slower, suggesting that facile reversibility of the bond between the distal histidine and the heme iron is needed to allow both substrate binding and heme iron reduction. On the other hand, catalysis driven by dithionite is limited by SO2 center dot-bold /boldconcentrations and is similar for all of these proteins, suggesting that dithionite is not a good reducing agent for evaluation of the catalytic properties of hemoglobins.
机译：植物植物是植物六环血红蛋白，具有可逆协调组氨酸侧链的血红素铁的配体结合位点。它们介导电子转移反应，例如一氧化氮清除，并且在还原亚硝酸盐和羟胺时特别有效。以前与植物植物的工作仅集中在这些反应的单一失误中，并且没有揭示是否在完全催化循环中起突出的作用。这项工作表征了使用两种不同的化学还原剂对氨基胺减少羟胺的稳态植物植物催化。测量K-M和K（猫）值针对水稻植物肽，马肌球蛋白，人类神经球蛋白和水稻植物霉蛋白突变蛋白，其中六丙烯酸己醛已被亮氨酸（PHYT：H73L）所取代。结果表明，苄基Viologen驱动的植物植物催化仅受到远端组氨酸的解离速率常数的限制。这与单周转实验中的速率限制一致，并证明羟胺结合的动力学，而不是植物植物的减少，最终得到了反应。通过缺乏或具有更紧密的六链六种的蛋白质的催化较慢，表明远端组氨酸和血红素铁之间的粘合的容易可逆性是允许衬底结合和血红素铁还原。另一方面，由DITHIONITE驱动的催化受到SO2中心点的限制为SO2中心点。 ＆ / bold＆浓度和对所有这些蛋白质相似，表明二硫代酮不是评估血红蛋白的催化性质的良好还原剂。

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  • 来源
    《Biochemistry》 |2018年第32期|共9页
  • 作者

    Alagurajan Jagannathan; Athwal Navjot Singh; Hargrove Mark S.;

  • 作者单位

    Iowa State Univ Roy J Carver Dept Biochem Biophys &

    Mol Biol Ames IA 50011 USA;

    Iowa State Univ Roy J Carver Dept Biochem Biophys &

    Mol Biol Ames IA 50011 USA;

    Iowa State Univ Roy J Carver Dept Biochem Biophys &

    Mol Biol Ames IA 50011 USA;

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  • 正文语种 eng
  • 中图分类 生物化学;
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