Lipid Metabolism in Helminth Parasites III. Biosynthesis and Interconversion of Fatty Acids by Hymenolepis diminuta (Cestoda)

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Abstract
The in vitro rate of incorporation of l-14c-acetate into the lipids of H. diminuta was significant, but lower than that of 1-14C-stearate. Palmitate, oleate, and linoleate were incorporated more rapidly than stearate. Most of the absorbed fatty acids appeared in the triglycerides, in which their relative abundance paralleled their rate of incorporation. No conversion of oleic and linoleic acids to other acids was observed. Most of the palmitic and stearic acids were also unchanged, but small amounts were converted to higher (C20, 22, 24, 26) saturated acids. In contrast to the fatty acids, acetate was incorporated primarily into saturated and unsaturated acids of the phospho- and glycolipids. No evidence was obtained for de novo synthesis, as stearic was the lowest molecular weight acid containing appreciable amounts of the acetate carbon, which was also present, in higher relative specific activities, in C20, 22, 24, and 26 saturated acids. Analysis of the carbon dioxide collected during decarboxylation of each of these acids supported the conclusion that acetate carbon was incorporated via chain-lengthening rather than by de novo synthesis. Although conclusive evidence was not obtained, it is also improbable that H. diminuta can synthesize unsaturated fatty acids. The results are interpreted in terms of biochemical adaptations of the adult parasite to its essentially anaerobic existence in the rat intestine.