Phytosterol biosynthesis pathway in Mortierella alpina

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 H-1 NMR spectroscopy, The principal sterol of the mycelium was cholesta-5, 24-dienol (desmosterol) (83%), with lesser amounts of 24 beta-methyl-cholesta-5,25(27)-dienol (codisterol) (2%), 24-methyl-desmosterol (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-H-2(3) for 6 days, generated 3 H-2-24-methyl(ene) sterols, [C28-H-2(2)]24(28)-methylenecholesterol, [C28-H-2(3)]24-methylcholesta-5,24-dienol and [C28-H-2(3)]24 beta-methyl-cholesta-5,25(27)-dienol. The formation of the 24-methyl sterols seems to be catalyzed by the direct methylation of a common Delta(24)-acceptor sterol thereby bypassing the intermediacy of an isomerization step for rearrangement of the Delta(24(28))-bond to Delta(25(25))-position as operates in Asco-mycetes fungi and all plants. (c) 2006 Elsevier Ltd. All rights reserved.