海水中のアミノ酸・タンパク質の分布と挙動 (1994年度日本海洋学会賞受賞記念講演)

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In this paper, my recent works on the organic nitrogen compounds, i.e. distribution and behavior of protein and DON in seawater and the amino acid sequence of metal binding peptide induced in marine diatom are described. The vertical profiles of dissolved protein and free amino acid show higher values at surface productive layer than those at deeper layer, as well as particulate protein. The protein is constituted of relatively low molecular weight fraction in the range of 10^3〜10^4 at surface layer. The concentration gradually decreases with depth and keep nearly a constant level, in which high molecular weight fractions above 10^5 is enriched at the layer below 1000m depth. The changes of molecular nature are interpreted from the origin of protein and the alteration during vertical transport of sinking particles. The vertical profiles of DON are almost similar tendency in the samples collected from 33 stations in the north Pacific Ocean. The regional variation of DON is also small. The average DON concentration is in the range from 6.4±1.9 μ M at the surface to 2.9±1.9 μ M below 200m, decreasing with depth. The DON concentrations are nearly constant below 200m depth. In the upper water, DON exists as labile nitrogen compounds which can easily be decomposed by oceanic bacteria. In the middle and the deep waters, however, DON exists more as biologically refractive compounds. This suggests that a significant source of DIN is not DON, though about 25% of DIN depends upon DON above 200m depth, estimating from correlation between AOU and DON. Many studies conducted to date have shown that heavy metals have detrimental effects on organisms. However, many of them are resistant to certain amounts of those metals. It is known that a metallothionein containing high amount of sulfur amino acid is induced in animal tissues. In the case of marine diatom, Phaeodactylum tricornutum, a different kind of small peptide is induced in the cytosol of cells under the presence of cadminm in seawater medium. The peptide is consisted of three kinds of amino acid, i.e. γ-Glutamic acid, Cystein and Glycine. The sequence of the amino acid is (γ-Glu-Cys)n-Gly, where n=4 to 5. This peptide is named as phytochelatine, which is also found in a terrestrial plant (Grill et al., 1985). The behavior at various cadmium concentration and the possibility of induction under the natural cadmium concentration levels are also discussed.
日本海洋学会の論文

海水中のアミノ酸・タンパク質の分布と挙動 (1994年度日本海洋学会賞受賞記念講演)

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