The enzyme system for the entrance of ^<14>CO_2 in the dark CO_2-fixation of brown algae

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概要

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• High activity of phosphoenolpyruvate (PEP)-carboxykinase, or ADP : oxalacetate (OAA) carboxy-lyase activity (a kind of EC 4. 1. 1. 32) was discovered in enzyme extracts or partially purified preparations obtained from the brown algae, Eisenia bicyclis, Dictyota dichotoma. Spatoglossum pacificum; and Hizikia fusiformis. Enzyme activities were determined by measuring the radioactivity incorporated in the products of dark ^<14>CO_2-fixation and by spectrophotometric determinations. Except for the low activity of "malic enzyme" (EC 1, 1. 1. 40), no activities of other carboxylases, i.e. PEP-carboxylase, PEP-carboxytransphosphorylase, and pyruvate carboxylase could be detected in algal extracts prepared under various conditions. Malate dehydrogenase (EC 1. 1. 1. 37), fumarase (EC 4. 2. 1. 2), and glutamic : oxalacetic transaminase (EC 2. 6. 1. 1) were also detected. The algal PEP-carboxykinase required ADP and Mn^<2+> for maximum activity in the carboxylation reaction; and ATP and Mn^<2+>, but not GTP, for maximum activity in both the decarboxylation and OAA-^<14>CO_2-exchange reactions. The optimum pH of purified PEP-carboxykinase was in the region of 7.0 to 7.3 in both the carboxylation and decarboxylation reactions, and its Km values for HCO_3^-, PEP, and ADP were 10 mM, 0.3 mM, and 0.07 mM, respectively, in the carboxylation reaction, and values for OAA and ATP were 0.05 mM and 0.4 mM, respectively, in the decarboxylation reaction. Furthermore, the decarboxylation reaction was markedly inhibited by 20 mM HCO_3^-. The physiological role of PEP-carboxykinase as the enzyme responsible for the entrance reaction of the dark CO_2-fixation is discussed.

• 日本植物生理学会の論文

著者

• Nisizawa Kazutosi

  Department Of Botany Faculty Of Science Tokyo Kyoiku University

• Akagawa Hisayoshi

  Department Of Botany Faculty Of Science Tokyo Kyoiku University:(present)department Of Antibiotics T

• Akagawa Hisayoshi

  Department Of Bioactive Molecules National Institute Of Infectious Diseases

• Ikawa Tomoyoshi

  Department Of Botany Faculty Of Science Tokyo Kyoiku University

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