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

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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.