Kletzin A, Adams M W
Department of Biochemistry and Molecular Biology, University of Georgia, Athens 30602-7229, USA.
FEMS Microbiol Rev. 1996 Mar;18(1):5-63. doi: 10.1016/0168-6445(95)00025-9.
Tungsten (atomic number 74) and the chemically analogous and very similar metal molybdenum (atomic number 42) are minor yet equally abundant elements on this planet. The essential role of molybdenum in biology has been known for decades and molybdoenzymes are ubiquitous. Yet, it is only recently that a biological role for tungsten has been established in prokaryotes, although not as yet in eukaryotes. The best characterized organisms with regard to their metabolism of tungsten are certain species of hyperthermophilic archaea (Pyrococcus furiosus and Thermococcus litoralis), methanogens (Methanobacterium thermoautotrophicum and Mb. wolfei), Gram-positive bacteria (Clostridium thermoaceticum, C. formicoaceticum and Eubacterium acidaminophilum), Gram-negative anaerobes (Desulfovibrio gigas and Pelobacter acetylenicus) and Gram-negative aerobes (Methylobacterium sp. RXM). Of these, only the hyperthermophilic archaea appear to be obligately tungsten-dependent. Four different types of tungstoenzyme have been purified: formate dehydrogenase, formyl methanufuran dehydrogenase, acetylene hydratase, and a class of phylogenetically related oxidoreductases that catalyze the reversible oxidation of aldehydes. These are carboxylic reductase, and three ferredoxin-dependent oxidoreductases which oxidize various aldehydes, formaldehyde and glyceraldehyde 3-phosphate. All tungstoenzymes catalyze redox tungsten in these enzymes is bound by a pterin moiety similar to that found in molybdoenzymes. The first crystal structure of a tungsten- or pterin-containing enzyme, that of aldehyde ferredoxin oxidoreductase from P. furiosus, has revealed a catalytic site with one W atom coordinated to two pterin molecules which are themselves bridged by a magnesium ion. The geochemical, ecological, biochemical and phylogenetic basis for W- vs. Mo-dependent organisms is discussed.
钨（原子序数74）以及化学性质类似且极为相似的金属钼（原子序数42）是地球上含量较少但同样丰富的元素。钼在生物学中的重要作用已为人所知数十年，含钼酶普遍存在。然而，直到最近才确定钨在原核生物中具有生物学作用，而在真核生物中尚未确定。在钨代谢方面研究最充分的生物是某些嗜热古菌（激烈火球菌和嗜热栖热菌）、产甲烷菌（嗜热自养甲烷杆菌和沃氏甲烷杆菌）、革兰氏阳性菌（热醋酸梭菌、甲酸醋酸梭菌和嗜酸真杆菌）、革兰氏阴性厌氧菌（巨大脱硫弧菌和乙炔还原菌）以及革兰氏阴性需氧菌（甲基杆菌属RXM菌株）。其中，只有嗜热古菌似乎绝对依赖钨。已纯化出四种不同类型的钨酶：甲酸脱氢酶、甲酰基甲烷呋喃脱氢酶、乙炔水合酶，以及一类在系统发育上相关的氧化还原酶，它们催化醛的可逆氧化。这些酶包括羧基还原酶，以及三种氧化各种醛、甲醛和3-磷酸甘油醛的铁氧化还原蛋白依赖性氧化还原酶。所有钨酶都催化氧化还原反应，这些酶中的钨与一个蝶呤部分结合，该蝶呤部分类似于在含钼酶中发现的蝶呤部分。来自激烈火球菌的醛铁氧化还原蛋白氧化还原酶是首个含钨或含蝶呤酶的晶体结构，它揭示了一个催化位点，其中一个钨原子与两个蝶呤分子配位，这两个蝶呤分子本身由一个镁离子桥接。本文讨论了依赖钨与依赖钼的生物的地球化学、生态学、生物化学和系统发育基础。
