DEVELOPMENTAL REGULATION OF STEROL BIOSYNTHESIS IN ZEA-MAYS
DEVELOPMENTAL REGULATION OF STEROL BIOSYNTHESIS IN ZEA-MAYS
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作者：
GUO, DA;VENKATRAMESH, M;NES, WD
从玉米(Zea Mays)中分离得到了61个甾醇和五环三萜类化合物，并用层析和光谱方法进行了表征。检查了几个植物部分：种子、花粉、培养的下胚轴细胞、根、胚芽鞘(鞘)和叶片。通过研究放射性示踪剂([2-C-14]甲戊酸、[2-C-14]乙酸酯和[2-H-3]乙酸酯)和稳定同位素(D2O)在植物上的反应途径和机理，我们发现羟甲基戊二酰辅酶A还原酶不是谷甾醇产生的限速酶。此外，我们观察到与甾醇侧链的C-24烷基化有关的个体发育位移和甾醇生物合成中的动力学同位素效应。叶片主要合成24α-乙基甾醇，鞘主要合成24-甲基甾醇，花粉具有中断的甾醇途径，积累24(28)-亚甲基甾醇，萌发种子缺乏活跃的从头途径。正常合成(Z)-24(28)-亚乙基-胆固醇的菜芽，在氚水中孵育后，合成重排的双键异构体--豆甾醇-5，23-二烯-3-β-醇。对24-乙基甾醇的质谱学和H-1核磁共振波谱的研究表明，在发育的这一阶段，起源于乙酰辅酶A并通过甲伐他酸合成甾醇的布洛赫-康福斯路线是不可行的。提出了一种产生类固醇的替代途径，
Sixty-one sterols and pentacyclic triterpenes have been isolated and characterized by chromatographic and spectral methods from Zea mays (corn). Several plant parts were examined; seed, pollen, cultured hypocotyl cells, roots, coleoptiles (sheaths), and blades. By studying reaction pathways and mechanisms on plants fed radiotracers ([2-C-14]mevalonic acid, [2-C-14]acetate, and [2-H-3]acetate), and stable isotopes (D2O), we discovered that hydroxymethylglutaryl CoA reductase is not ''the'' rate-limiting enzyme of sitosterol production. Additionally, we observed an ontogenetic shift and kinetic isotope effect in sterol biosynthesis that was associated with the C-24 alkylation of the sterol side chain. Blades synthesized mainly 24 alpha-ethyl-sterols, sheaths synthesized mainly 24-methyl-sterols, pollen possessed an interrupted sterol pathway, accumulating 24(28)-methylene-sterols, and germinating seeds were found to lack an active de novo pathway. Shoots, normally synthesizing (Z)-24(28)-ethylidine-cholesterol, after incubation with deuterated water, synthesized the rearranged double-bond isomer, stigmasta-5,23-dien-3 beta-ol. Examination of the mass spectrum and H-1 nuclear magnetic resonance spectrum of the deuterated 24-ethyl-sterol indicated the Bloch-Cornforth route originating with acetyl-CoA and passing through mevalonic acid to sterol was not operative at this stage of development. An alternate pathway giving rise to sterols is proposed,