The stereochemistry of hexahydroprenol, ubiquinone and ergosterol biosynthesis in the mycelium of Aspergillus fumigatus Fresenius |
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Authors: | K. J. Stone and F. W. Hemming |
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Affiliation: | Department of Biochemistry, University of Liverpool |
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Abstract: | 1. The mycelium of Aspergillus fumigatus has been shown to incorporate mevalonate into squalene, ubiquinone, ergosterol and hexahydroprenol. 2. The 3H/14C ratio in ubiquinone, biosynthesized from [2-14C-(4R)-4-3H1]mevalonate, is the same as in the squalene; essentially no 3H was incorporated from [2-14C-(4S)-4-3H1]mevalonate, indicating the biosynthesis of biogenetically trans-isoprene units. 3. The 3H/14C ratio for ergosterol (from `4R-mevalonate') was 3:5, showing that the proton at C-24 is not lost during alkylation of the side chain; it probably migrates to C-25. 4. As 3H from both mevalonates was incorporated into the hexahydroprenols the biosynthesis of both cis- and trans-isoprene units must occur. 5. The saturated ω- and ψ-isoprene units are shown to be biogenetically trans, as are two of the unsaturated residues. 6. The saturated α- and unsaturated β-isoprene residues are both biogenetically cis. 7. An inexplicable loss of approximately half of the olefinic protons from the cis-portion of hexahydroprenol occurs; possible reasons for this loss are discussed. 8. Increase in chain length of the hexahydroprenols is by a cis addition. 9. A biosynthesis of hexahydroprenols by addition of cis-isoprene units to all-trans-geranylgeranyl pyrophosphate, or a dihydro or tetrahydro derivative thereof, is suggested. |
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