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Pathway and the enzymes for biosynthesis of mugineic acid family in iron-deficient barley roots.

缺铁大麦根中麦根酸家族生物合成的途径和酶。

基本信息

批准号：
07660075
负责人：
KAWAI Shigenao
金额：
$ 0.45万
依托单位：
Iwate University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07660075/
关键词：
Mugineic acid Biosynthesis Glucose Methionine Homoserine Glycerol Sulfur Metabolism Iron Deficiency SH基プロパジルグリシン

项目摘要

The aim of this research project was to clarify the biosynthetic pathway of mugineic acid family of phytosiderophores (MAs), which is secreted by the roots of grasses and solubilizes iron in rhizosphere under iron-deficient condition.At first, the experiment was conducted to investigate the pathway of MAs biosynthesis which is derived from glucose. In the experiment, it was indicated that ^<14>C of glucose was converted to MAs rapidly. The rate for conversion of glucose into MAs was as high as that into organic acids in TCA cycle or amino acids in protein. The feeding experiments of excised barley roots was conducted using glucose whose carbons were specifically labeled by stable isotope ^<13>C or radio isotope ^<14>C.The results suggested that all of 6 carbons in a glucose molecule were incorporated specifically into a MAs molecule.The feeding experiment with ^<14>C-homoserine suggested that homoserine may not be a precursor of MAs. In the subsequent experiment about the relationship between sulfur metabolism and MAs biosynthesis, glucose was suggested to be converted to MAs by way of methionine bypassing homoserine. In addition, the valuable result was obtained which shows that glycerol is converted to MAs rapidly.In the experiments using inhibitors of metabolism, it was noted that DTNB,PCBA and beta-cyanoalanine increase the incorporation of ^<14>C of methionine into MAs.As a preliminary step for purification of enzymes catalyzing MAs biosynthesis, cell free system derived from roots of iron-deficient barley was prepared and used for feeding experiments with ^<14>C-labeled compounds. The results showed that homocysteine strongly inhibited the incorporation of ^<14>C of methionine into MAs. It was suggested that homocysteine may competitively inhibit MAs biosynthesis as an analogue of methionine. It may be a useful information for the succeeding experiment to purify the enzymes of MAs biosynthesis.

本研究旨在阐明缺铁条件下禾本科植物根系分泌的植物铁载体mugineic acid（MAs）的生物合成途径。实验结果表明，<14>葡萄糖的~（13）C迅速转化为甲基丙烯酸甲酯。葡萄糖转化为甲基丙烯酸的速率与转化为TCA循环中的有机酸或蛋白质中的氨基酸的速率一样高。用稳定性同位素~（13）C或放射性同位素~（13）C标记的葡萄糖对离体大麦根进行了摄食实验<13><14>，结果表明，葡萄糖分子中的6个碳都被特异性地掺入到MAs分子中，~（13）<14>C-高丝氨酸的摄食实验表明，高丝氨酸可能不是MAs的前体。在随后的硫代谢与MAs生物合成之间的关系的实验中，建议葡萄糖通过甲硫氨酸绕过高丝氨酸的方式转化为MAs。在代谢抑制剂的作用下，DTNB、PCBA和β-氰基丙氨酸能促进蛋氨酸的~（13）<14>C掺入到MAs中。作为纯化催化MAs生物合成的酶的初步步骤，制备了缺铁大麦根的无细胞系统，并用于~（13）<14>C标记化合物的饲养实验。结果表明，同型半胱氨酸强烈抑制<14>甲硫氨酸的^ C掺入MA。结果表明，同型半胱氨酸可能作为蛋氨酸的类似物竞争性抑制MAs的生物合成。这为后续的MAs生物合成酶的纯化提供了有用的信息。