Everard J D, Cantini C, Grumet R, Plummer J, Loescher W H
Department of Horticulture, Michigan State University, East Lansing 48824-1325, USA.
Plant Physiol. 1997 Apr;113(4):1427-35. doi: 10.1104/pp.113.4.1427.
Compared with other primary photosynthetic products (e.g. sucrose and starch), little is known about sugar alcohol metabolism, its regulation, and the manner in which it is integrated with other pathways. Mannose-6-phosphate reductase (M6PR) is a key enzyme that is involved in mannitol biosynthesis in celery (Apium graveolens L.). The M6PR gene was cloned from a leaf cDNA library, and clonal authenticity was established by assays of M6PR activity, western blots, and comparisons of the deduced amino acid sequence with a celery M6PR tryptic digestion product. Recombinant M6PR, purified from Escherichia coli, had specific activity, molecular mass, and kinetic characteristics indistinguishable from those of authentic celery M6PR. Sequence analyses showed M6PR to be a member of the aldo-keto reductase superfamily, which includes both animal and plant enzymes. The greatest sequence similarity was with aldose-6-phosphate reductase (EC 1.1.1.200), a key enzyme in sorbitol synthesis in Rosaceae. Developmental studies showed M6PR to be limited to green tissues and to be under tight transcriptional regulation during leaf initiation, expansion, and maturation. These data confirmed a close relationship between the development of photosynthetic capacity, mannitol synthesis, and M6PR activity.
与其他主要光合产物（如蔗糖和淀粉）相比，人们对糖醇代谢、其调控以及它与其他途径整合的方式了解甚少。甘露糖-6-磷酸还原酶（M6PR）是芹菜（Apium graveolens L.）中参与甘露醇生物合成的关键酶。从叶片cDNA文库中克隆了M6PR基因，并通过M6PR活性测定、蛋白质免疫印迹以及将推导的氨基酸序列与芹菜M6PR胰蛋白酶消化产物进行比较来确定克隆的真实性。从大肠杆菌中纯化的重组M6PR具有与天然芹菜M6PR无法区分的比活性、分子量和动力学特性。序列分析表明M6PR是醛酮还原酶超家族的成员，该超家族包括动物和植物酶。与醛糖-6-磷酸还原酶（EC 1.1.1.200）序列相似性最高，醛糖-6-磷酸还原酶是蔷薇科山梨醇合成中的关键酶。发育研究表明M6PR仅限于绿色组织，并且在叶片起始、扩展和成熟过程中受到严格的转录调控。这些数据证实了光合能力的发育、甘露醇合成和M6PR活性之间的密切关系。
