Emission mechanism of monohalomethanes from marine organisms and its effect on ozone depletion

大气中的甲基溴被认为是可破坏平流层臭氧的气态溴的最大储存库，海洋中的甲基溴来源估计为3.5x10^<10>g/年。尽管如此，甲基溴的源和汇仍然没有得到协调。大部分问题在于量化和绘制海洋来源。最近对海洋大型藻类和微型藻类的调查显示，甲基溴和甲基碘直接由海洋浮游植物Pavlova gyrans产生，而甲基碘和微量甲基溴则由大型藻类Papenfusiella kuromo和Sargassum horneri释放。浮游植物直接产生甲基溴的证据支持了微藻在海洋甲基溴排放中的作用。从S-腺苷-L-甲硫氨酸（SAM）的无细胞提取物中合成卤代甲烷的P.gyrans，P.kuromo和S. horneri。这一机制对应于三种藻类体内卤代甲烷的释放。我们已经揭示了一些新的酶从P. gyrans的特性。

Atmospheric methyl bromide is considered to be the largest reservoir of gaseous bromine that can destroy stratospheric ozone, and the ocean source of methyl bromide has been estimated at 3.5x10^<10> g/year. Nonetheless, the sources and sinks of methyl bromide are not still reconciled. Much of the problem lies in quantifying and mapping the oceanic source. A recent survey of marine macro- and microalgae has revealed that methyl bromide and methyl iodide are directly produced by the marine phytoplankton, Pavlova gyrans, and that methyl iodide and a trace amount of methyl bromide are released by the macroalgae Papenfusiella kuromo and Sargassum horneri. The evidence of direct production of methyl bromide from a phytoplankton supports the microalgae role in oceanic methyl bromide emission. Methyl halides were synthesized from S-adenosyl-L-methionine (SAM) in cell-free extracts of P.gyrans, P.kuromo and S.horneri. This mechanism corresponded to the emission of methyl halides from the three algae in vivo. We have revealed some properties of the novel enzyme from P.gyrans.