Developmental regulation of sterol biosynthesis inZea mays
| Autor: | Mylavarapu Venkatramesh, De-An Guo, W. D. Nes |
|---|---|
| Rok vydání: | 1995 |
| Předmět: |
Alkylation
Campesterol Mevalonic Acid Mevalonic acid Acetates Biology Models Biological Plant Roots Zea mays Biochemistry Mass Spectrometry Hypocotyl chemistry.chemical_compound polycyclic compounds Tissue Distribution Carbon Radioisotopes Chromatography High Pressure Liquid chemistry.chemical_classification Stigmasterol Phytosterol Organic Chemistry Phytosterols food and beverages Cell Biology Sitosterols Sterol Coleoptile Enzyme chemistry Seeds Hydroxymethylglutaryl CoA Reductases lipids (amino acids peptides and proteins) Oxidation-Reduction Plant Shoots |
| Zdroj: | Lipids. 30:203-219 |
| ISSN: | 1558-9307 0024-4201 |
| DOI: | 10.1007/bf02537823 |
| Popis: | 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-(14)C]mevalonic acid, [2-(14)C]acetate, and [2-(3)H]acetate), and stable isotopes (D2O), we discovered that hydroxymethylgutaryl 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 1H 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. |
| Databáze: | OpenAIRE |
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