Phosphoenolpyruvate carboxylase in cucumber (Cucumis sativus L.) roots under iron deficiency:: activity and kinetic characterization
Phosphoenolpyruvate carboxylase in cucumber (Cucumis sativus L.) roots under iron deficiency:: activity and kinetic characterization
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DOI：
10.1093/jexbot/51.352.1903
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发表时间：
2000-11-01
影响因子：
6.9
通讯作者：
Zocchi, G
中科院分区：
文献类型：
--
作者：
De Nisi, P;Zocchi, G
研究了铁饥饿条件下黄瓜根系磷酸烯醇式丙酮酸羧化酶（PEPCase）活性的变化。从植物中提取的酶的存在和不存在的Fe的特征在于动力学和生化。在不存在Fe的情况下，可提取的PEPC酶活性增加了4倍。这种增加开始约5天后，铁饥饿。蛋白质印迹分析表明，存在两个多肽的表观分子量为103和108 kDa。在开始时，这两种多肽同样存在于对照和缺铁根中。铁饥饿10天后，增加是明显的和关注的，特别是，103 kDa的多肽，其增强约3倍，相对于对照。再供应铁的Fe饥饿的根降低了酶的活性和浓度的控制值。动力学参数测定表明，从缺铁根中提取的酶的底物Km值相同，而Vmax增加了4倍。此外，pH值的变化和别构调节剂苹果酸和葡萄糖-6-磷酸的反应是不同的。动力学数据，PEPCase比活性和PEPCase多肽浓度的增加似乎表明，在铁缺乏的酶调节可能是，在部分，在转录水平上施加。
Phosphoenolpyruvate carboxylase (PEPCase) activity was investigated in cucumber roots grown under iron starvation. The enzyme extracted from plants grown in the presence and in the absence of Fe was characterized both kinetically and biochemically. Extractable PEPCase activity was increased by 4-fold in the absence of Fe. This increase began about 5 d after Fe starvation. Western blot analysis revealed the presence of two polypeptides with apparent molecular masses of 103 and 108 kDa. At the beginning both the polypeptides were equally present in the control and in the Fe-deficient roots. After 10 d of Fe starvation the increase was clearly evident and concerned, in particular, the polypeptide of 103 kDa whose enhancement was around 3-fold with respect to the control. Re-supply of iron to Fe-starved roots decreased both the activity and the concentration of the enzyme to the control values. Determination of kinetic parameters revealed that the K-m values for the substrates were the same, while the V-max was increased by four times for the enzyme extracted from Fe-deficient roots. Also the responses to pH changes and to the allosteric modulators malate and glucose-6-phosphate were different. The kinetic data, the increase in PEPCase specific activity and in the PEPCase polypeptides concentration seem to indicate that under Fe deficiency the enzyme regulation might be, in part, exerted at the transcriptional level.