Differences in intermediary energy metabolism between juvenile and adult Fasciola hepatica

Abstract

A comparison of glucose catabolism by juvenile and adult liver flukes, Fasciola hepatica, showed that in the adult the cytosolic degradation of glucose via phosphoenolpyruvate carboxykinase (PEPCK) was the most important route, whereas in the freshly excysted juvenile a large part was degraded via pyruvate kinase (PK). However, it was also shown that the adult did not exclusively use the PEPCK pathway, nor did the juvenile exclusively use the PK pathway. When the juvenile was forced to anaerobic functioning it produced propionate and acetate just like the adult, but this did not imply that it switched to the pathways of the adult: the pathway via PK remained important. Malic enzyme (NADP(H)-dependent) was demonstrated to be present in the cytosol and in the mitochondria of both juveniles and adults. These enzyme activities enable the parasite to use a mixture of maiate and pyruvate in any ratio as substrate for the mitochondrial production of propionate and acetate. Pyruvate dismutation was important in the anaerobically functioning juvenile, whereas in the adult malate was the major, but not the only mitochondrial substrate. The pH profiles of PK and PEPCK showed that the pathway of PEP metabolism at the PK/PEPCK branchpoint can be regulated by the pH. However, the end products of glucose breakdown were not dependent on the pH. During its development, the liver fluke will gradually be forced to anaerobic functioning. At first, the acidic end product will favour a partitioning of PEP at the PK/PEPCK branchpoint towards malate formation. Later, a lasting predominance of the PEPCK pathway occurs as PK activity almost completely disappears. During the development of F. hepatica also a transition in the mitochondria occurs: at the acetyl-coenzyme A branchpoint a switch from citrate to acetate formation could be demonstrated. The most likely mechanism of this change is discussed.

Purification and characterization of phosphoenolpyruvate carboxykinase fromRaillietina echinobothrida, a cestode parasite of the domestic fowl

“…multilocularis (McManus and Smyth, 1982). Also, in the adult liver fluke Fasciola hepatica and the nematode Dipetalonema viteae , PEPCK takes part in degradation of glucose rather than in gluconeogenesis (Christie et al 1987; Tielens et al 1987) although, in contrast, the involvement of PEPCK in glycolysis was not conclusive in the blood fluke, Schistosoma mansoni (Tielens et al 1991). PEPCK was first identified in the chicken liver where it catalyses the decarboxylation of oxaloacetate (Utter and Kurahashi, 1954), and since then the enzyme has been purified and characterized from various vertebrate sources (Ballard and Hanson, 1969; Noce and Utter, 1975; Hebda and Nowak, 1982 a ).…”

Molecular identification, immunolocalization, and characterization of Clonorchis sinensis triosephosphate isomerase

“…sinensis invade the definitive host and then transform into juvenile flukes and adults, they also need abundant energy through glycometabolism. Other research studies have shown that most of the glucose was degraded in the freshly excysted metacercariae of F. hepatica (Tielens et al 1987). CsTIM was also expressed in vesicle, eggs, and testicle of adult worm (Fig.…”

The enigmatic presence of all gluconeogenic enzymes inSchistosoma mansoniadults

“…This could indicate a strong preference of the PK over the PEPCK pathway in the degradation of glucose. It should be noted, however, that the absolute PEPCK activity is only 5 times higher in a comparable homogenate of adult Fasciola hepatica, a trematode that is well known for the extensive use of the PEPCK pathway (Tielens, Van den Heuvel & Van den Bergh, 1987).…”