Han Qian, Beerntsen Brenda T, Li Jianyong
Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
J Insect Physiol. 2007 Mar;53(3):254-63. doi: 10.1016/j.jinsphys.2006.09.004. Epub 2006 Sep 17.
Oxidation of tryptophan to kynurenine and 3-hydroxykynurenine (3-HK) is the major catabolic pathway in mosquitoes. However, 3-HK is oxidized easily under physiological conditions, resulting in the production of reactive radical species. To overcome this problem, mosquitoes have developed an efficient mechanism to prevent 3-HK from accumulating by converting this chemically reactive compound to the chemically stable xanthurenic acid. Interestingly, 3-HK is a precursor for the production of compound eye pigments during the pupal and early adult stages; consequently, mosquitoes need to preserve and transport 3-HK for compound eye pigmentation in pupae and adults. This review summarizes the tryptophan oxidation pathway, compares and contrasts the mosquito tryptophan oxidation pathway with other model species, and discusses possible driving forces leading to the functional adaptation and evolution of enzymes involved in the mosquito tryptophan oxidation pathway.
色氨酸氧化生成犬尿氨酸和3-羟基犬尿氨酸（3-HK）是蚊子主要的分解代谢途径。然而，3-HK在生理条件下很容易被氧化，从而产生活性自由基。为克服这一问题，蚊子已进化出一种有效机制，通过将这种化学反应性化合物转化为化学性质稳定的黄尿酸来防止3-HK积累。有趣的是，3-HK是蛹期和成虫早期复眼色素生成的前体；因此，蚊子需要保存并运输3-HK用于蛹期和成虫的复眼色素沉着。本综述总结了色氨酸氧化途径，将蚊子的色氨酸氧化途径与其他模式物种进行了比较和对比，并讨论了导致蚊子色氨酸氧化途径中相关酶功能适应和进化的可能驱动力。
