Nematodes biosynthesis

Next to fumarate reduction, some organisms use specific reactions in lipid biosynthesis as an electron sink to maintain redox balance in anaerobically functioning mitochondria. In anaerobic mitochondria two variants are known the production of branched-chain fatty acids and the production of wax esters. The parasitic nematode Ascaris suum reduces fumarate in its anaerobic mitochondria, but instead of only producing acetate and succinate or propionate, like most other parasitic helminths, this organism also use the intermediates acetyl-CoA and propionyl-CoA to form branched-chain fatty acids (Komuniecki et al. 1989). This pathway is similar to reversal of P-oxidation and a complex mixture of the end products acetate, propionate, succinate and branched-chain fatty acids is excreted. In this pathway, the... 

Metagenomic approaches have been used to study metabolites produced by bacterial symbionts of marine animals, insects, and nematodes. The literature now provides several examples where DNA-based strategies targeting specific genetic loci have enabled the isolation and cloning of biosynthetic gene clusters encoding for the biosynthesis of important symbiont-associated molecules such as pederin, onn amide A, bryostatins, trunkamide, theopalauamide, and the patellamides. These studies are the focus of another chapter in this series and therefore will not be discussed here. 

In the nematodes the five soluble enzymes of pyrimidine de novo biosynthesis were found in crude extracts of Nippostrongylus brasiliensis and Trichuris muris (81). The first enzyme of de novo synthesis, glutamine-dependent carbamoyl-phosphate synthetase, was deteeted in Ascaris ovary extracts (115), and aspartate transcarbamoylase activity, the second enzyme of de novo synthesis, was found in A. suum (113). 

Selkirk, M. E. (1991) Structure and biosynthesis of cuticular proteins of lymphatic fllarial parasites. In Parasitic Nematodes Antigens, Membranes, and Genes (ed. Kennedy, M. W.). Taylor amd Francis, Bristol, PA. 

Maduramicin (92), a polyether ionophore, has been found as a metabolite of Noccirdia and Actinomadura species [149]. Its structure was determined by X-ray crystallographic studies and an investigation of its biosynthesis revealed that it incorporated 8 acetate, 7 propionate units with 4 methoxy methyls derived from methionine. It displayed anti-malarial [150] and nematocidal activity (0.5-30 ppm) towards phyto- and animal-parasitic nematodes [151]. 

The symposium from which this book was developed was designed to review and present current research on the biosynthesis and metabolism of lipids in plants together with the chemistry and biochemistry of lipid interactions however, some presentations reported input from disciplines other than chemistry. This 22-chapter volume presents a loose classification of the papers presented at the symposium into four sections (1) Introduction, (2) Plant Lipid Metabolism and Plant-Plant Interactions, (3) Plant-Insect and Plant-Nematode Interactions, and (4) Plant-Microbial Interactions. 

Lack of De Novo Sterol Biosynthesis in Nematodes. The dietary requirement tor sterol results from the lack ofde novo sterol biosynthesis in nematodes. Species In which radiolabeled acetate or mevalonate are not converted to radiolabeled sterol Include T. aceti (14, 15), Caenorhabditls (15) and the animal parasites AscarTs (l6), Dirof aria immitis (17), and Brugia pahangi (17). On occasion, radiolabeled sterols Identified by thin-layer cRromatography have been detected from nematodes incubated with radiolabeled acetate in the lone case in which such compounds were further characterized by gas-liquid chromatography, the radiolabeled components possessed retention times much earlier than cholesterol (16). 

The composition and biosynthesis of chitin have been studied in insects such as mosquitoes, cockroaches, honeybees, silkworms. Drosophila melanogaster, Extatosoma tiaratum, Sipyloidea sipylus in terrestrial crustaceans such as Armadillidium vulgare, Porcellio scaber, and in nematodes (Anantaraman and Ravindranath 1976, Carlberg 1982, Veronico et al. 2001, Nemtsev et al. 2004, Moussian et al. 2005, Tauber 2005, Paulino et al. 2006, Hild et al. 2008). The composition and structure of their organic matrices are different from each other. 

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