Enzymes involved in the last steps of the biosynthesis of mannitol in brown algae |
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Authors: | Ikawa Tomoyoshi; Watanabe Tsuneo; Nisizawa Kazutosi |
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Institution: | Department of Botany, Faculty of Science, Tokyo Kyoiku University Otsuka, Tokyo, Japan |
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Abstract: | Mannitol-1-phosphate dehydrogenase (EC 1.1.1.17
EC]
) and mannitol-1-phosphatase(EC number yet unassigned) were detected in the brown algae,Spatoglossum pacificum and Dictyota dichotoma. The enzymes wereextracted from algal fronds and their properties were investigatedusing partially purified preparations. Mannitol-1-phosphatase shows maximum activity at pH 7. The enzymehad a narrow substrate specificity. The Km value for mannitol-1-phosphateis 8.3x104 M (30°C, pH 7.0). The enzyme is activatedby Mg++ and Mn++and is strongly inhibited by PCMB, Hg++and NaF. Mannitol-1-phosphate dehydrogenase showed maximum activitiesat pH values 6.5 and 10.2 in reductive and oxidative reactions,respectively. The dehydrogenase also showed narrow substratespecificity; mannitol-1-phosphate and NAD or fructose-6-phosphateand NADH2 are utilized, respectively, in oxidative and reductivereactions by the enzyme. Km values for these substrates andthe coenzymes are 2.5x104 M and 7.1x105 M forthe first pair and 2.8x104 M and 1.3x105 M forthe latter pair. This enzyme was strongly inhibited by PCMBand Hg++, but was only slightly affected by adenosine phosphates. Possible roles of these enzymes in the biosynthesis of mannitolin brown algae are discussed.
1 Contributions from the Shimoda Marine Biological Station ofTokyo Kyoiku University, No. 233. This work was supported inpart by a Grant-in-Aid for Co-operative Research from the Ministryof Education, Japan and in part by a grant to one of us (T.Ikawa) from the Matsunaga Science Foundation.
2 Present address: Chemical and Physical Laboratory, HoechstJapan Research Laboratory, Minamidai, Kawagoe, Japan. (Received February 22, 1972; ) |
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