Noordermeer M A, Veldink G A, Vliegenthart J F
Bijvoet Center for Biomolecular Research, Department of Bio-Organic Chemistry, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
Chembiochem. 2001 Aug 3;2(7-8):494-504. doi: 10.1002/1439-7633(20010803)2:7/8<494::AID-CBIC494>3.0.CO;2-1.
Plants continuously have to defend themselves against life-threatening events such as drought, mechanical damage, temperature stress, and potential pathogens. Nowadays, more and more similarities between the defense mechanism of plants and that of animals are being discovered. In both cases, the lipoxygenase pathway plays an important role. In plants, products of this pathway are involved in wound healing, pest resistance, and signaling, or they have antimicrobial and antifungal activity. The first step in the lipoxygenase pathway is the reaction of linoleic or linolenic acids with molecular oxygen, catalyzed by the enzyme lipoxygenase. The hydroperoxy fatty acids thus formed are highly reactive and dangerous for the plant and therefore further metabolized by other enzymes such as allene oxide synthase, hydroperoxide lyase, peroxygenase, or divinyl ether synthase. Recently, these enzymes have been characterized as a special class of cytochrome P450 enzymes. Hydroperoxide lyases cleave the lipoxygenase products, resulting in the formation of omega-oxo acids and volatile C6- and C9-aldehydes and -alcohols. These compounds are major contributors to the characteristic "fresh green" odor of fruit and vegetables. They are widely used as food flavors, for example, to restore the freshness of food after sterilization processes. The low abundance of these compounds in nature and the high demand make it necessary to synthesize them on a large scale. Lipoxygenase and hydroperoxide lyase are suitable biocatalysts for the production of "natural" food flavors. In contrast to lipoxygenase, which has been extensively studied, little is yet known about hydroperoxide lyase. Hydroperoxide lyases from different organisms have been isolated, and a few genes have been published lately. However, the structure and reaction mechanism of this enzyme are still unclear. The identification of this enzyme as a cytochrome P450 sheds new light on its structure and possible reaction mechanism, whereas recombinant expression brings a biocatalytic application into sight.
植物必须不断抵御诸如干旱、机械损伤、温度胁迫和潜在病原体等危及生命的事件。如今，植物和动物的防御机制之间越来越多的相似之处被发现。在这两种情况下，脂氧合酶途径都起着重要作用。在植物中，该途径的产物参与伤口愈合、抗虫性和信号传导，或者它们具有抗菌和抗真菌活性。脂氧合酶途径的第一步是亚油酸或亚麻酸与分子氧的反应，由脂氧合酶催化。由此形成的氢过氧脂肪酸具有高反应性，对植物来说是危险的，因此会被其他酶进一步代谢，如丙二烯氧化物合酶、氢过氧化物裂解酶、过氧合酶或二乙烯醚合酶。最近，这些酶被归类为一类特殊的细胞色素P450酶。氢过氧化物裂解酶裂解脂氧合酶产物，导致形成ω-氧代酸以及挥发性C6和C9醛类和醇类。这些化合物是水果和蔬菜特有的“清新绿色”气味的主要贡献者。它们被广泛用作食品香料，例如，用于恢复杀菌处理后食品的新鲜度。这些化合物在自然界中的低丰度和高需求使得大规模合成它们成为必要。脂氧合酶和氢过氧化物裂解酶是生产“天然”食品香料的合适生物催化剂。与已被广泛研究的脂氧合酶相比，人们对氢过氧化物裂解酶的了解还很少。来自不同生物体的氢过氧化物裂解酶已被分离出来，最近也有一些基因被公布。然而，这种酶的结构和反应机制仍然不清楚。将这种酶鉴定为细胞色素P450为其结构和可能的反应机制提供了新的线索，而重组表达则为其生物催化应用带来了曙光。
