The tricarboxylic acid cycle in L3 Teladorsagia circumcincta: metabolism of acetyl CoA to succinyl CoA

Nematodes, like other species, derive much of the energy for cellular processes from mitochondrial pathways including the TCA cycle. Previously, we have shown L-3 Teladorsagia circumcincta consume oxygen and so may utilise a full TCA cycle for aerobic energy metabolism. We have assessed the relative activity levels and substrate affinities of citrate synthase, aconitase, isocitrate dehydrogenase (both NAD(+) and NADP(+) specific) and alpha-ketoglutarate dehydrogenase in homogenates of L-3 T. circumcincta. All of these enzymes were present in homogenates. Compared with citrate synthase, low levels of enzyme activity and low catalytic efficiency was observed for NAD(+) isocitrate dehydrogenase and especially alpha-ketoglutarate dehydrogenase. Therefore, it is likely that the activity of these to enzymes regulate overall metabolite flow through the TCA cycle, especially when [NAD(+)] limits enzyme activity. Of the enzymes tested, only citrate synthase had substrate affinities which were markedly different from values obtained from mammalian species. Overall, the results are consistent with the suggestion that a full TCA cycle exists within L3 T. circumcincta. While there may subtle variations in enzyme properties, particularly for citrate synthase, the control points for the TCA cycle in L-3 T. circumcincta are probably similar to those in the tissues of their host species. (C) 2011 Elsevier Inc. All rights reserved.