Oba K, Ishikawa S, Nishikawa M, Mizuno H, Yamamoto T
Department of Food Biochemistry, Nagoya Women's University.
J Biochem. 1995 Jan;117(1):120-4. doi: 10.1093/oxfordjournals.jbchem.a124697.
L-Galactono-gamma-lactone dehydrogenase (L-galactono-gamma-lactone:ferricytochrome c oxidoreductase [EC 1.3.2.3], GLDHase) which catalyzes the terminal step in the biosynthesis of L-ascorbic acid (AsA) has been purified from roots of sweet potato (Ipomoea batatas L., cv. Kintoki). Highly purified preparation of the GLDHase was obtained by three column chromatography steps with a recovery of ca. 1%, after solubilization from mitochondria in sweet potato roots. SDS-PAGE exhibited a single band at 56 kDa. In the native state, the apparent molecular mass of the enzyme was 56 kDa, based on a Sephadex G-100 gel filtration. The pI and optimum pH values were 5.8 and 7.9, respectively. The Km value for L-galactono-gamma-lactone was 0.12 mM. Substrate inhibition was obtained at concentrations greater than 4.2 mM. The enzyme was inhibited by p-chloromercuribenzoate (PCMB) and acriflavine, and the inhibition of acriflavine was diminished by the addition of FAD or FMN. The only effective substrate for the GLDHase was L-galactono-gamma-lactone.
L-半乳糖酸-γ-内酯脱氢酶（L-半乳糖酸-γ-内酯：铁细胞色素c氧化还原酶[EC 1.3.2.3]，GLDHase）催化L-抗坏血酸（AsA）生物合成的最后一步，已从甘薯（Ipomoea batatas L.，品种锦光）根中纯化得到。从甘薯根中的线粒体溶解后，通过三步柱色谱法获得了高度纯化的GLDHase制剂，回收率约为1%。SDS-PAGE显示在56 kDa处有一条单一的条带。在天然状态下，根据Sephadex G-100凝胶过滤，该酶的表观分子量为56 kDa。pI和最适pH值分别为5.8和7.9。L-半乳糖酸-γ-内酯的Km值为0.12 mM。在浓度大于4.2 mM时出现底物抑制。该酶被对氯汞苯甲酸（PCMB）和吖啶黄素抑制，加入FAD或FMN可减弱吖啶黄素的抑制作用。GLDHase唯一有效的底物是L-半乳糖酸-γ-内酯。
