Tobacco Nectarin III is a bifunctional enzyme with monodehydroascorbate reductase and carbonic anhydrase activities
Tobacco Nectarin III is a bifunctional enzyme with monodehydroascorbate reductase and carbonic anhydrase activities
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DOI：
10.1023/b:plan.0000036373.84579.13
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发表时间：
2004-02-01
影响因子：
5.1
通讯作者：
Thornburg, RW
中科院分区：
文献类型：
--
作者：
Carter, CJ;Thornburg, RW
烟草植物分泌一系列有限的蛋白质（花蜜）到它们的花蜜中。Nectarin II（NEC 2; 35 kD）和Nectarin III（NEC 3; 40 kD）蛋白的N-末端测序显示，它们都与薯蓣皂苷（薯蓣块茎的主要可溶性蛋白）具有同一性。这些序列还揭示了NEC 2是NEC 3的分解产物。使用这些N-末端肽序列，简并寡核苷酸的设计，允许部分NEC 3 cDNA的分离。然后将该cDNA用于探测蜜腺特异性cDNA文库，并分离出全长NEC 3 cDNA克隆。全序列分析证实NEC 3是薯蓣皂苷样蛋白。MALDI-TOF质谱指纹的胰蛋白酶肽从纯化的NEC 3证实，这种蛋白质是由分离的cDNA编码。NEC 3同时具有碳酸酐酶和单脱氢抗坏血酸还原酶活性。基于RT-PCR的表达分析表明，NEC 3转录本在整个蜜腺发育以及其他花器官中表达。建议在花蜜的pH值和氧化平衡的维护功能进行了讨论。
Tobacco plants secrete a limited array of proteins (nectarins) into their floral nectar. N-terminal sequencing of the Nectarin II (NEC2; 35 kD) and the Nectarin III (NEC3; 40 kD) proteins revealed that they both share identity with dioscorin, the major soluble protein of yam tubers. These sequences also revealed that NEC2 is a breakdown product of NEC3. Using these N-terminal peptide sequences, degenerate oligonucleotides were designed that permitted the isolation of a partial NEC3 cDNA. This cDNA was then used to probe a nectary specific cDNA library and a full-length NEC3 cDNA clone was isolated. Complete sequence analysis confirmed the identity of NEC3 as a dioscorin-like protein. MALDI-TOF mass spectrometric fingerprinting of tryptic peptides derived from the purified NEC3 confirmed that this protein was encoded by the isolated cDNA. NEC3 was shown to possess both carbonic anhydrase and monodehydroascorbate reductase activities. RT-PCR based expression analyses demonstrated that NEC3 transcript is expressed throughout nectary development as well as in other floral organs. A proposed function in the maintenance of pH and oxidative balance in nectar is discussed.