Planta

, Volume 201, Issue 2, pp 173–178

Characterization of mannitol metabolism in the mangrove red algaCaloglossa leprieurii (Montagne) J.Agardh

  • Ulf Karsten
  • Kevin D. Barrow
  • Oliver Nixdorf
  • John A. West
  • Robert J. King
Article

DOI: 10.1007/BF01007701

Cite this article as:
Karsten, U., Barrow, K.D., Nixdorf, O. et al. Planta (1997) 201: 173. doi:10.1007/BF01007701

Abstract

A metabolic pathway, known as the mannitol cycle in fungi, has been identified as a new entity in the eulittoral mangrove red algaCaloglossa leprieurii (Montagne) J. Agardh. Three specific enzymes, mannitol-1-phosphate dehydrogenase (Mt1PDH; EC 1.1.1.17), mannitol-1-phosphatase (MtlPase; EC 3.1.3.22), mannitol dehydrogenase (MtDH; EC 1.1.1.67) and one nonspecific hexokinase (HK; EC 2.7.1.1) were determined and biochemically characterized in cell-free extracts. Mannitol-1-phosphate dehydrogenase showed activity maxima at pH 7.0 [fructose-6-phosphate (F6P) reduction] and pH 8.5 [oxidation of mannitol-1-phosphate (Mt1P)], and a very high specificity for both carbohydrate substrates. TheKm values were 1.4 mM for F6P, 0.09 mM for MOP, 0.020 mM for NADH and 0.023 mM for NAD+. For the dephosphorylation of MOP, MtlPase exhibited a pH optimum at 7.2, aKm value of 1.2 mM and a high requirement of Mg2+ for activation. Mannitol dehydrogenase had activity maxima at pH 7.0 (fructose reduction) and pH 9.8 (mannitol oxidation), and was less substrate-specific than Mt1PDH and MtlPase, i.e. it also catalyzed reactions in the oxidative direction with arabitol (64.9%), sorbitol (31%) and xylitol (24.8%). This enzyme showedKm values of 39 mM for fructose, 7.9 mM for mannitol, 0.14 mM for NADH and 0.075 mM for NAD+. For the non-specific HK, only theKm values for fructose (0.19 mM) and glucose (7.5 mM) were determined. The activities of the anabolic enzymes Mt1PDH and MtlPase were always at least two orders of magnitude higher than those of the degradative enzymes, indicating a net carbon flow towards a high intracellular mannitol pool. The function of mannitol metabolism inC. leprieurii as a biochemical adaptation to the environmental extremes in the mangrove habitat is discussed.

Key words

CaloglossaHexokinaseMannitol-1-phosphate dehydrogenaseMannitol-1-phosphataseMannitol dehydrogenaseOsmolyte metabolism

Abbreviations

F6P

fructose-6-phosphate

HK

hexokinase

Mt1P

mannitol-1-phosphate

Mt1PDH

mannitol-1-phosphate dehydrogenase

Mt1Pase

mannitol-1-phosphatase

MtDH

mannitol dehydrogenase

Copyright information

© Springer-Verlag 1997

Authors and Affiliations

  • Ulf Karsten
    • 1
  • Kevin D. Barrow
    • 2
  • Oliver Nixdorf
    • 3
  • John A. West
    • 4
  • Robert J. King
    • 1
  1. 1.School of Biological ScienceUniversity of New South WalesSydneyAustralia
  2. 2.School of Biochemistry and Molecular GeneticsUniversity of New South WalesSydneyAustralia
  3. 3.Department of Biology, Marine BotanyUniversity of BremenBremenGermany
  4. 4.School of BotanyUniversity of MelbourneParkvilleAustralia
  5. 5.Alfred-Wegener-Institute for Polar and Marine ResearchBremerhavenGermany