title: Nuclear demethylation and C-24 alkylation during ergosterol biosynthesis in Saccharomyces cerevisiae.
abstract: The role of 4,4-dimethylzymosterol (3), 4,4-dimethylfecosterol (4) and 31-norlanosterol (5) in the biosynthesis of ergosterol in Saccharomyces cerevisiae has been investigated. The synthesis of 4 and 5 coupled with the availability of 3 facilitated a search for these sterols in commercial yeast sterol concentrates, fresh laboratory grown yeast and fresh brewery grown yeast. Sterol 4 was not detected in any of these mixtures whereas 5 was found in the first and last and 3 was present in all three sources investigated. Investigation of incorporation of [2-3H]lanosterol into 3, 4 and 5 revealed significant incorporation into 3 but neither 4 nor 5. This observation suggests the principle pathway for ergosterol biosynthesis initially involved 1 leads to 3 leads to 7. Incubation of a mixture of [2,4-3H]zymosterol and [26,27-14C]lanosterol with S. cerevisiae revealed that during the initial phases of aerobic growth the major route from 7 to ergosterol involves zymosterol (11) but as 11 accumulates 4 alpha-methyl-24-methylenezymosterol (8) assumes equal importance.
mesh_terms: D002849:Chromatography, Gas; D002855:Chromatography, Thin Layer; D004875:Ergosterol / Q000096:biosynthesis*; D007810:Lanosterol / Q000378:metabolism; D013058:Mass Spectrometry; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D013055:Spectrophotometry, Infrared; D013261:Sterols / Q000378:metabolism; D013997:Time Factors
chemical_list: D013261:Sterols; D007810:Lanosterol; D004875:Ergosterol