Effect of sterol replacement in vivo on the fatty acid composition of Tetrahymena
The addition of ergosterol to cultures of Tetrahymena pyriformis results in (a) the accumulation of the sterol by the cells; (b) the inhibition of the synthesis of the pentacyclic triterpenoid alcohol, tetrahymanol; (c) the replacement of tetrahymanol by ergosterol in the ciliate membranes. The dry...
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Veröffentlicht in: | The Journal of biological chemistry 1975-09, Vol.250 (17), p.6998-7005 |
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Zusammenfassung: | The addition of ergosterol to cultures of Tetrahymena pyriformis results in (a) the accumulation of the sterol by the cells;
(b) the inhibition of the synthesis of the pentacyclic triterpenoid alcohol, tetrahymanol; (c) the replacement of tetrahymanol
by ergosterol in the ciliate membranes. The dry weight and lipid content of sterol-supplemented ciliates did not differ from
the controls. Examination of the lipid classes revealed no change in composition except for a higher content of ergosterol
in supplemented cells than tetrahymanol in control cultures. The relative proportions of triglycerides, the major classes
of polar lipids, 1-alkyl phospholipids and phosphonolipids, appeared unaltered. A complex array of fatty acids is found in
this ciliate. Several acids not reported previously in this organism were isolated and identified, and the novel fatty acid
18:2 delta 6, 11, was found in substantial amounts. Ergosterol supplementation altered the proportions of the fatty acids,
although not all lipid classes were affected to the same extent. The changes noted were of three general types: (a) a shortening
of the fatty acyl chain length in the acids of the normal series; (b) a lowering in the degree of unsaturation; (c) a discrimination
between two isomers of lionoleate, 18:2 delta 6, 11 and 18:2 delta 9, 12. The former is elevated in the presence of ergosterol
while the latter is depressed. Each class of polar lipids has a distinctive fatty acid composition. Among the glycerophospholipids,
cardiolipin and phosphatidylcholine were least affected, while the mixture of 1-alkyl-2-acyl-sn-glycero-3-(2-aminoethyl)-phosphonate
and 1,2-diacyl-sn-glycero-3-(2-aminoethyl)-phosphonate was most markedly altered. Sphingolipid fatty acid composition was
influenced by ergosterol supplementation. Two changes were noted: (a) a reduction in the length of the hydrocarbon chain;
(b) an increase in the proportion of alpha-hydroxy acids. The impact of ergosterol on the fatty acid composition of the polar
lipids may be on fatty acid biosynthesis, on incorporation of fatty acids, or on the turnover rates of the fatty acyl groups.
Ergosterol is concentrated in the ciliary (limiting) membrane, as are the polar lipids most affected. This localization allows
the speculation that the change in fatty acid composition may be related to the maintenance of optimal membrane properties
upon the introduction of the sterol. |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1016/S0021-9258(19)41031-4 |