Morita Tomotake, Takegawa Kaoru, Yagi Toshiharu
Department of Bioresources Science, Faculty of Agriculture, Kochi University, Nankoku, Kochi 783-8502.
J Biochem. 2004 Feb;135(2):225-30. doi: 10.1093/jb/mvh026.
Pyridoxal (PL) reductase encoded by the plr1(+) gene practically catalyzes the irreversible reduction of PL by NADPH to form pyridoxine (PN). The enzyme has been suggested to be involved in the salvage synthesis of pyridoxal 5'-phosphate (PLP), a coenzyme form of vitamin B(6), or the excretion of PL as PN from yeast cells. In this study, a PL reductase-disrupted (plr1 Delta) strain was constructed and its phenotype was examined. The plr1 Delta cells showed almost the same growth curve as that of wild-type cells in YNB and EMM media. In EMM, the plr1 Delta strain became flocculent at the late stationary phase for an unknown reason. The plr1 Delta cells showed low but measurable PL reductase activity catalyzed by some other protein(s) than the enzyme encoded by the plr1(+) gene, which maintained the flow of "PL --> PN --> PNP --> PLP" in the salvage synthesis of PLP. The total vitamin B(6) and pyridoxamine 5'-phosphate contents in the plr1 Delta cells were significantly lower than those in the wild-type ones. The percentages of the PLP amount as to the other vitamin B(6) compounds were similar in the two cell types. The amount of PL in the culture medium of the disruptant was significantly higher than that in the wild-type. In contrast, PN was much higher in the latter than the former. The plr1 Delta cells accumulated a 6.1-fold higher amount of PL than the wild-type ones when they were incubated with PL. The results showed that PL reductase encoded by the plr1(+ )gene is involved in the excretion of PL after reducing it to PN, and may not participate in the salvage pathway for PLP synthesis.
由plr1(+)基因编码的吡哆醛（PL）还原酶实际上催化NADPH对PL进行不可逆还原，形成吡哆醇（PN）。有人认为该酶参与维生素B6的辅酶形式——磷酸吡哆醛（PLP）的补救合成，或者参与酵母细胞将PL以PN形式排出。在本研究中，构建了PL还原酶缺失（plr1Δ）菌株并检测其表型。在YNB和EMM培养基中，plr1Δ细胞的生长曲线与野生型细胞几乎相同。在EMM中，plr1Δ菌株在稳定期末期不知为何变得絮凝。plr1Δ细胞显示出较低但可测量的PL还原酶活性，该活性由plr1(+)基因编码的酶以外的其他一些蛋白质催化，这在PLP的补救合成中维持了“PL→PN→PNP→PLP”的流程。plr1Δ细胞中的总维生素B6和磷酸吡哆胺含量显著低于野生型细胞。两种细胞类型中PLP量相对于其他维生素B6化合物的百分比相似。缺失突变体培养基中的PL量显著高于野生型。相反，PN在野生型中比在缺失突变体中高得多。当plr1Δ细胞与PL一起孵育时，它们积累的PL量比野生型细胞高6.1倍。结果表明，由plr1(+)基因编码的PL还原酶参与将PL还原为PN后PL的排出，可能不参与PLP合成的补救途径。
