Simcock, D.C., Walker, L.R., Pedley, K.C., Simpson, H.V., and Brown, S. (2007) The glyoxylate cycle in Ostertagia (Teladorsagia) circumcincta. New Zealand Journal of Zoology, 34 (2). pp. 153-154.

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Abstract

Ostertagia (Teladorsagia) circumcincta is a nematode parasite which infects the abomasum of sheep and goats. The utilisation of substrates for energy production in O. circumcincta is largely unknown. This parasite has been shown to consume oxygen, and have a full glycolytic and TCA cycle in both L3 and adult stages, although the metabolism of carbohydrates in adults appears to be more geared towards an anaerobic pathway. As well as glycogen, O. circumcincta also contains high levels of stored lipid in both L3 and adult stages, which could also be utilised to provide energy. However, the relative importance of glycogen and lipid for energy production is unknown: in the L3, in which nutrient intake is thought to be restricted by the presence of the sheath; or the adult, in which lipid metabolism may be restricted by oxygen supply. The key enzymes of the glyoxylate cycle, malate synthase and isocitrate would allow this parasite to convert lipid to glucose for metabolism via glycolysis. The enzyme phosphoenolpyruvate carboxykinase (PEPCK) has also been detected in both L3 and adult O. circumcincta. Although this enzyme is typically associated with anaerobic metabolism in nematode parasites, it is also central to gluconeogenesis. As the O. circumcincta has a full TCA cycle and consumes oxygen, gluconeogenesis may be the key function of PEPCK in this parasite species, particularly in L3s. The activity of the glyoxylate cycle along relative levels of glycogen and lipid in L3 and adults of different ages will be discussed.

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