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  • Title: Metabolism of delta24-sterols by yeast mutants blocked in removal of the C-14 methyl group.
    Author: Pierce AM, Mueller RB, Unrau AM, Oehlschlager AC.
    Journal: Can J Biochem; 1978 Aug; 56(8):794-800. PubMed ID: 356938.
    Abstract:
    We have investigated the metabolism of exogenously provided delta24-sterols by whole cell cultures of a polyene-resistant mutant (D10) of Candida albicans blocked at removal of the C-14 methyl group. Comparison of the relative efficiencies of transmethylation at C-24 of selected sterol substrates revealed the following substrate preferences of the Candida delta24-sterol methyltransferase (EC 2.1.1.41): zymosterol greater than 4alpha-methylzymosterol greater than 14alpha-methylzymosterol. Exogenous 4,4-dimethylzymosterol was not transmethylated by mutant D10. Incorporation of the 14C-labelled methyl group of S-adenosyl-L-[methyl-14C]methionine into the sterols of a D10 culture preloaded with zymosterol indicated that zymosterol was a better (40 X) substrate than endogenous lanosterolmfeeding zymosterol to D10 and a polyene-resistant strain of Saccharomyces cerevisiae (Nys-P100) that was also blocked at removal of the C-14 methyl group gave 24-methyl sterols possessing delta22 and ring B unsaturation. Mutant D10 was able to produce ergosterol from zymosterol whereas Nys-P100 produced ergosta-7,22-dienol. When grown in the presence of 3 micrometer 25-aza-24,25-dihydrozymosterol, a known inhibitor of the delta24-sterol methyltransferase, Nys-P100 accumulated 14alpha-methylzymosterol, a minor metabolite in this mutant under normal growth conditions and hitherto unidentified as a yeast sterol.
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