PLANT PHYSIOLOGY , Vol 114, Issue 1 231-236, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Characterization and Purification of an Aldose Reductase from the Acidophilic and Thermophilic Red Alga Galdieria sulphuraria
W. Gross, P. Seipold and C. Schnarrenberger
Institut fur Pflanzenphysiologie und Mikrobiologie, Freie Universitat Berlin, Konigin-Luise-Strasse 12-16, D-14195 Berlin, Germany
The acidophilic and thermophilic red alga Galdieria sulphuraria is able to
grow heterotrophically on at least six different pentoses. These pentoses
are reduced in the cell to pentiols by an NADP-dependent aldose reductase.
The pentiols are then introduced into the oxidative pentose phosphate
pathway via NAD-dependent polyol dehydrogenases and pentulokinases. The
aldose reductase was purified 130-fold to apparent homogeneity by column
chromatography. The enzyme is a homodimer of about 80 kD, as estimated by
size-exclusion chromatography and from the sedimentation behavior. The
Michaelis constant values for D-xylose (27 mM), D-ribose (29 mM), D-lyxose
(30 mM), and D-arabinose (38 mM) were about three to five times lower than
for the L-forms of the sugars. The activity of the enzyme with hexoses,
deoxysugars, and sugar phosphates was only about 5 to 10% of the rate with
pentoses. In the reverse reaction the activity was low and only detectable
with pentiols. No activity was measured with NAD(H) as the cosubstrate in
either direction.