| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1993: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1992: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Research Abstract |
The concentration of biogenic dimethylsulphide(DMS) in the sea water in Maizuru Bay in one year ranged from 0.04 tO 18.0 mug DMS/l. Although these concentrations of DMS coincide slightly with the incidence of the concentration of chlorophyll a, a good correlation was obtained between concentration of DMS and chlorophyll a in red tide waters of dinoflagellates such as Prorocentrum micans and Gymnodinium nagasakiense. Rough estimates for the average flux of DMS from coastal water to the atmosphere during the summer are of the order of 10^3 mg S/m^<2.>d, a 100-fold increse over th winter flux. DMS in surface seawater and vertical hydrographic profiles were also determined in the western, subtropical Pacific Ocean during the cruises of the Seisui-maru and Hakuho-maru. The vertical distribution of DMS in the euphotic zone follows that of primary production, with a maximum at or near the ocean surfce and a decrease with depth. Below the level of 1% light penetration, DMS levels decline gradu
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ally. The mean DMS concentrations in the surface water of the sea off Japan and the tropical and subtropical Pacific Ocean were 611 and 265 ng DMS/l, respectively. Since DMS is the major volatile sulphur compound in the ocean, it is suggested that estimated DMS transfer across the sea-air interface contributes significantly to the atmospheric sulphur budget.
The tertiary sulphonium compound dimethylthiopropanoic acid(DMTP, = dimethylpropiothetine) is a precursor of DMS.Methionine is an efficient precursor for the biosynthesis of DMTP in the dinoflagellate Crypthecodinium cohnii. The methyl group, C-3 and C-4 carbons, and sulphur atoms of methionine were incorporated into DMTP, whereas C-1 carbon of methionine was not incorporated into DMTP.The results indicate that methionine is converted to DMTP by decarboxylation, deamination, oxidation, and methylation.
Methionine decarboxylase was completely purified from C.cohnii and characterized. The molecular weight of this enzyme is about 240 KDa, consit of 2 subunits. Km value is 16.3 mM.The enzyme requires pyridoxalphosphate. The N-terminal amino acid sequence of the enzyme is Ala-Leu-X-Trp-Ser-Asp-lle-Ser-Arg-----. Less
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