Function of halogenating enzymes and a biogenic halogen cycle in nature

研究发现，一些海藻（包括Cortina）产生的溴仿是一种化感物质，能清除藻类表面的附生生物，尤其是硅藻;另一方面，一些大型和微型海藻（如Paviova sp.）也能释放出一卤甲烷，这些海藻产生一卤甲烷的分子特征表明，SAM：卤离子甲基转移酶反应参与了该反应。然而，这些酶非常不稳定，因此，进一步表征是困难的。最近，我们发现了一种具有相对稳定的SAM：卤离子甲基转移酶的海洋微生物，并建立了分离纯化方法，这是首次从海洋微生物中分离纯化SAM：卤离子甲基转移酶。海洋环境，特别是海洋微藻的溴甲烷排放可以解释大气中溴甲烷的含量。在本研究项目中，我们从土壤微生物恶臭假单胞菌中克隆了编码一种新的Co^2+激活的溴过氧化物酶的基因。重组酶催化苯乙烯和茚的溴化反应，得到相应的外消旋溴代醇化合物。同时发现该酶对D-乙酰硫代异丁酸甲酯具有酯酶活性，表明该酶是一种独特的双功能酶。

Bromoform produced by some marine algae including Corallina was found to be a kind of allelochemical eliminating the epiphytic organisms, especially, diatoms on the algal surface.On the other hand, monohalomethanes have been observed to emit from some marine macro- and microalgae such as Paviova sp. Molecular characterization to form monohalomethanes in these algae have revealed that SAM : halide ion methyltransferase reaction participates in the reaction. However, these enzymes were very unstable, therefaore, further characterization had been difficult. Recently, we have found a marine microalga having the relatively stable enzyme and established the purification procedures to isolate it. This is the first work to purify the SAM : halide ion methyltransferase from marine microalga. The emission of methyl bromide from marine environment, especially from marine microalgae, could explain the amount of methyl bromide in the atmosphere.In this research project, we have cloned the gene encoding a novel Co^<2+>-activating bromoperoxidase from a soil microorganism, Pseudomonas putida. The recombinant enzyme catalyzed the brominating reactions of styrene and indene giving the corresponding racemic bromohydrin compounds. It was also found that the enzyme has a esterase activity toward methyl D-acethylthioisobutyrate, suggesting that the enzyme is an unique bifunctional enzyme.