Functional Characterization of D-Galacturonic Acid Reductase, a Key Enzyme of the Ascorbate Biosynthesis Pathway, from Euglena gracilis
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<small>D</small>-Galacturonic acid reductase, a key enzyme in ascorbate biosynthesis, was purified to homogeneity from <I>Euglena gracilis</I>. The enzyme was a monomer with a molecular mass of 38–39 kDa, as judged by SDS–PAGE and gel filtration. Apparently it utilized NADPH with a <I>K</I>m value of 62.5±4.5 μ<small>M</small> and uronic acids, such as <small>D</small>-galacturonic acid (<I>K</I>m=3.79±0.5 m<small>M</small>) and <small>D</small>-glucuronic acid (<I>K</I>m=4.67±0.6 m<small>M</small>). It failed to catalyze the reverse reaction with <small>L</small>-galactonic acid and NADP<SUP>+</SUP>. The optimal pH for the reduction of <small>D</small>-galacturonic acid was 7.2. The enzyme was activated 45.6% by 0.1 m<small>M</small> H<SUB>2</SUB>O<SUB>2</SUB>, suggesting that enzyme activity is regulated by cellular redox status. No feedback regulation of the enzyme activity by <small>L</small>-galactono-1,4-lactone or ascorbate was observed. N-terminal amino acid sequence analysis revealed that the enzyme is closely related to the malate dehydrogenase families.
- Agricultural and Biological Chemistry
Agricultural and Biological Chemistry 70(11), 2720-2726, 2006-11-23
Japan Society for Bioscience, Biotechnology, and Agrochemistry