Phytosterol biosynthesis pathway in Mortierella alpina

• Published in: Phytochemistry (Oxford) 2006-08, Vol.67 (16), p.1716-1721
• Main Authors: David Nes, W., Nichols, Shawn D.
• Format: Article
• Language: English
• Subjects: biochemical pathways; Biological and medical sciences; biosynthesis; Cholesterol; Ergosterol biosynthesis; Fundamental and applied biological sciences. Psychology; Fungal evolution; Gas Chromatography-Mass Spectrometry; Isotope labeling; Magnetic Resonance Spectroscopy; Metabolism; Metabolism. Physicochemical requirements; Mortierella; Mortierella - metabolism; Mortierella alpina; oleaginous fungi; Phytosterols - biosynthesis; Plant physiology and development; Sterol methyltransferase; sterol methyltransferases; sterols; Zygomycota
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2006.02.023

The construction of three 24-methyl sterol side chains by the action of a common sterol methyltransferase was suggested by chemical identification studies and incubation of Mortierella alpina mycelium with methionine- methyl- 2H 3. The Zygomycetes fungus Mortierella alpina was cultured to growth arrest to assess the phytosterol biosynthesis pathway in a less-advanced fungus. The mycelium was found to produce 13 sterols, but no ergosterol. The sterol fractions were purified to homogeneity by HPLC and their identifies determined by a combination of GC–MS and 1H NMR spectroscopy. The principal sterol of the mycelium was cholesta-5, 24-dienol (desmosterol) (83%), with lesser amounts of 24β-methyl-cholesta-5,25(27)-dienol (codisterol) (2%), 24-methyldesmosterol (6%), 24(28)-methylene cholesterol (3%) and lanosterol (3%) and several other minor compounds (3%). The total sterol accounted for approximately 0.07% of the mycelial dry wt. Mycelium fed methionine- methyl- 2H 3 for 6 days, generated 3 2H-24-methyl(ene) sterols, [C28- 2H 2]24(28)-methylenecholesterol, [C28- 2H 3]24-methylcholesta-5,24-dienol and [C28- 2H 3]24β-methyl-cholesta-5,25(27)-dienol. The formation of the 24-methyl sterols seems to be catalyzed by the direct methylation of a common Δ 24-acceptor sterol thereby bypassing the intermediacy of an isomerization step for rearrangement of the Δ 24(28)-bond to Δ 25(25)-position as operates in Ascomycetes fungi and all plants.