Journal of Lipid Research, Vol 28, 1424-1433, Copyright © 1987 by Lipid Research, Inc.
Metabolism of saturated fatty acids by Paramecium tetraurelia
DE Rhoads, O Honer-Schmid and ES Kaneshiro
Department of Biological Sciences, University of Cincinnati, OH 45221.
Paramecium requires oleate for growth. The phospholipids of the ciliate
contain high concentrations of palmitate and 18- and 20-carbon unsaturated
fatty acids. We previously showed that radiolabeled oleate is desaturated
and elongated to provide these 18- and 20-carbon unsaturated acids. We now
report on saturated fatty acid (SFA) metabolism in Paramecium. Radiolabeled
palmitate and stearate were incorporated directly into cellular
phospholipids with little or no desaturation and/or elongation.
Radiolabeled acetate, malonate, pyruvate, citrate, or glucose added to
cultures were not incorporated into cellular phospholipid fatty acids
indicating that these exogenously supplied putative precursors were not
utilized for fatty acid synthesis by Paramecium. Radiolabel from octanoate
or hexanoate appeared in fatty acyl groups of phospholipids, possibly by
partial beta-oxidation and reincorporation of the label. Under oleate-free
conditions in which cultures do not grow, radiolabel from these shorter
chain SFA were beta-oxidized and preferentially used for the formation of
arachidonate, the major end-product of fatty acid synthesis in Paramecium.
Cerulenin inhibited culture growth apparently by inhibiting de novo fatty
acid synthesis. Cerulenin-treated cells did not incorporate radioactivity
from [1-14C]octanoate into esterified palmitate. However, total
saponifiable phospholipid fatty acids, including SFA, per cell increased
under these conditions.
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