d-Mannitol dehydrogenase and d-mannitol-1-phosphate dehydrogenase in Platymonas subcordiformis: some characteristics and their role in osmotic adaptation |
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Authors: | D F E Richter G O Kirst |
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Institution: | (1) Fachbereich Biologie, Universität Bremen, NW 2, Leobener Strasse, D-2800 Bremen 33, Federal Republic of Germany |
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Abstract: | d-Mannitol-1-phosphate dehydrogenase (EC 1.1.1.17) and d-mannitol dehydrogenase (EC 1.1.1.67) were estimated in a cell-free extract of the unicellular alga Platymonas subcordiformis Hazen (Prasinophyceae), d-Mannitol dehydrogenase had two activity maxima at pH 7.0 and 9.5, and a substrate specifity for d-fructose and NADH or for d-mannitol and NAD+. The K
m values were 43 mM for d-fructose and 10 mM for d-mannitol. d-Mannitol-1-phosphate dehydrogenase had a maximum activity at pH 7.5 and was specific for d-fructose 6-phosphate and NADH. The K
m value for d-fructose 6-phosphate was 5.5 mM. The reverse reaction with d-mannitol 1-phosphate as substrate could not be detected in the extract. After the addition of NaCl (up to 800 mM) to the enzyme assay, the activity of d-mannitol dehydrogenase was strongly inhibited while the activity of d-mannitol-1-phosphate dehydrogenase was enhanced. Under salt stress the K
m values of the d-mannitol dehydrogenase were shifted to higher values. The K
m value for d-fructose 6-phosphate as substrate for d-mannitol-1-phosphate dehydrogenase remained constant. Hence, it is concluded that in Platymonas the d-mannitol pool is derectly regulated via alternative pathways with different activities dependent on the osmotic pressure.Abbreviations Fru6P
d-fructose 6-phosphate
- Mes
2-(N-morpholino)ethanesulfonic acid
- MT-DH
d-mannitol-dehydrogenase
- MT1P-DH
d-mannitol-1-phosphate dehydrogenase
- Pipes
1,4-piperazinediethanesulfonic acid
- Tris
2-amino-2-(hydroxymethyl)-1,3-propanediol |
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Keywords: | d-Mannitol dehydrogenase" target="_blank">d-Mannitol dehydrogenase d-Mannitol-1-phosphate dehydrogenase" target="_blank">d-Mannitol-1-phosphate dehydrogenase Osmotic adaptation Platymonas |
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