Accumulation and Utilization of Dissolved Inorganic Carbon by a Marine Unicellular Coccolithophorid, Emiliania huxleyi : MEMBRANES AND BIOENERGETICS : STRUCTURE AND FUNCTION OF CELLS
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概要
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The mechanism for utilization of dissolved inorganic carbon (DIC) was investigated in the marine unicellular calcareous alga Emiliania huxleyi, grown with constant aeration. The apparent K_<0.5> (DIC), the concentration of DIC which attains one-half of the maximum velocity of apparent photosynthesis, for photosynthetic evolution of O_2, measured under saturating light, was 5.5 mM (55 /μM for CO_2) at pH 8.0 and 25℃. The value of K_<0.5> was not affected by inhibitors of carbonic anhydrase (CA), and an electrometric assay of CA showed that the enzyme was not involved in photosynthesis in this alga. The rate of photosynthetic fixation of ^<14>C-DIC into acid-stable products was about 20 times higher than that into CaCO_3, irrespective of the external concentration of DIC. In short-term experiments, ^<14>C-DIC was usually incorporated into the internal pool of DIC (IIC) to concentrations up to 13 to 16 times higher than that of the external DIC. CO_2 added externally was utilized mainly for fixation of CO_2 and accumulation of IIC. By contrast, HCO_3^- was utilized mainly for production of CaCO_3 and accumulation of IIC. Incorporation of ^<14>C into IIC was partially suppressed by DCMU or in darkness but its transfer to CaCO_3 was unaffected. These results suggest that accumulation of IIC in this alga, even under ordinary circumstances, is only partially responsible for increasing the efficiency of utilization of DIC by photosynthetic fixation but may be most useful for the production of CaCO_3. (Hydroxyethylidene) bisphosphonic acid, an inhibitor of the growth of CaCO_3 crystals, completely suppressed production of CaCO_3. The accumulation of IIC was also partially sup-pressed, but photosynthetic fixation of CO_2 was enhanced. In a pulse-chase experiment with ^<14>C-DIC, ^<14>C incorporated into IIC and CaCO_3 in darkness was transferred to acid-stable products of photosynthesis in the light. These results suggest that ^<14>C-DIC in IIC and pre-formed CaCO_3 may be useful sources of carbon for fixation of CO_2-
- 日本植物生理学会の論文
著者
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Sekino Keisuke
Department of Biology, Faculty of Science, Niigata University
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Shiraiwa Yoshihiro
Department of Biology, Faculty of Science, Niigata University
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Sekino K
Niigata Univ. Niigata Jpn
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Sekino Keisuke
Department Of Biology Faculty Of Science Niigata University
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Shiraiwa Yoshihiro
Department Of Biochemistry Michigan State University:(present)department Of Biology Faculty Of Scien
関連論文
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