Vogt Ryan N, Steenkamp Daniel J
Division of Chemical Pathology, Department of Laboratory Medicine, University of Cape Town Medical School, Observatory, 7925, South Africa.
Biochem J. 2003 Apr 1;371(Pt 1):49-59. doi: 10.1042/BJ20021649.
It has recently been established that nitrosoglutathione is the preferred substrate of the glutathione-dependent formaldehyde dehydrogenase from divergent organisms. Trypanosomatids produce not only glutathione, but also glutathionylspermidine, trypanothione and ovothiol A. The formaldehyde dehydrogenase activity of Crithidia fasciculata was independent of these thiols and extracts possessed very low levels of nitrosothiol reductase activity with glutathione or its spermidine conjugates as the thiol component. Although ovothiol A did not form a stable nitrosothiol, it decomposed the S -nitroso groups of nitrosoglutathione (GSNO) and dinitrotrypanothione [T(SNO)(2)] with second-order rate constants of 19.12 M(-1) x s(-1) and 8.67 M(-1) x s(-1) respectively. The reaction of T(SNO)(2) with ovothiol A, however, accelerated to a rate similar to that seen with GSNO. Ovothiol A can act catalytically to decompose these nitrosothiols, although non-productive mechanisms exist. The catalytic phase of the reaction was dependent on the production of thiyl radicals, since it was abolished in the presence of 5,5-dimethyl-1-pyrroline- N -oxide and the formation of nitric oxide could be detected by means of the conversion of oxyhaemoglobin into methaemoglobin. The rate-limiting step in the catalytic process was the reduction of oxidized ovothiol species and, in this respect, T(SNO)(2) is a more efficient substrate than GSNO. Trypanothione decomposed GSNO with a second-order rate constant of 0.786 M(-1) x s(-1) and the major nitrogenous end product changed from nitrite to ammonia as the ratio of thiol to nitrosothiol increased. The results indicate that ovothiol A acts in synergy with trypanothione in the decomposition of T(SNO)(2).
最近已确定，亚硝基谷胱甘肽是来自不同生物体的谷胱甘肽依赖性甲醛脱氢酶的首选底物。锥虫不仅产生谷胱甘肽，还产生谷胱甘氨酰亚精胺、锥虫硫醇和卵硫醇A。克氏锥虫的甲醛脱氢酶活性与这些硫醇无关，提取物中以谷胱甘肽或其亚精胺共轭物作为硫醇成分时，亚硝基硫醇还原酶活性水平非常低。尽管卵硫醇A不会形成稳定的亚硝基硫醇，但它能分解亚硝基谷胱甘肽（GSNO）和二硝基锥虫硫醇[T(SNO)(2)]的S-亚硝基基团，二级速率常数分别为19.12 M(-1)×s(-1)和8.67 M(-1)×s(-1)。然而，T(SNO)(2)与卵硫醇A的反应加速至与GSNO反应时相似的速率。卵硫醇A可催化分解这些亚硝基硫醇，尽管存在非生产性机制。反应的催化阶段依赖于硫自由基的产生，因为在5,5-二甲基-1-吡咯啉-N-氧化物存在下该阶段被消除，并且一氧化氮的形成可通过氧合血红蛋白转化为高铁血红蛋白来检测。催化过程中的限速步骤是氧化型卵硫醇物种的还原，在这方面，T(SNO)(2)是比GSNO更有效的底物。锥虫硫醇以0.786 M(-1)×s(-1)的二级速率常数分解GSNO，随着硫醇与亚硝基硫醇的比例增加，主要含氮终产物从亚硝酸盐变为氨。结果表明，卵硫醇A与锥虫硫醇在分解T(SNO)(2)中协同作用。
