The enigmatic presence of all gluconeogenic enzymes in Schistosoma mansoni adults.
The activities of glucose-6-phosphatase (G6Pase), fructose-1,6-bisphosphatase (FBPase), phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase (PC) were determined in homogenates of adult Schistosoma mansoni worms and compared with the activities in homogenates of rat liver and rat skeletal muscle, tissues with a high and a low gluconeogenic capacity, respectively. All four gluconeogenic enzymes were present in S. mansoni. The enzymes were less active than in rat liver, but the activities of G6Pase, PEPCK and PC were at least an order of magnitude higher than in rat skeletal muscle whereas FBPase was approximately equally active in S. mansoni and in rat muscle. Experiments with 14C-labelled substrates or [14C]NaHCO3 failed to demonstrate the actual occurrence of gluconeogenesis in S. mansoni. Some possible other functions of the gluconeogenic enzymes were investigated. Experiments with inhibitors of PEPCK gave no indications that this enzyme was involved in the degradation of glucose. This was confirmed by 13C-NMR experiments which indicated that lactate was formed from phosphoenolpyruvate via the actions of pyruvate kinase and lactate dehydrogenase, and that PEPCK did not participate in the formation of lactate. Substrate cycling between fructose-6-dehydrogenase, and fructose-1,6-bisphosphate was demonstrated to occur in adult S. mansoni. This shows that FBPase participates in the glucose metabolism of this parasite.
Tielens
A G
AG
Laboratory of Veterinary Biochemistry, Utrecht University, The Netherlands.
Van der Meer
P
P
van den Heuvel
J M
JM
van den Bergh
S G
SG
D000818:Animals; D006597:Fructose-Bisphosphatase / Q000032:analysis; D005943:Gluconeogenesis; D005952:Glucose-6-Phosphatase / Q000032:analysis; D008099:Liver / Q000201:enzymology; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009132:Muscles / Q000201:enzymology; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000032:analysis; D011766:Pyruvate Carboxylase / Q000032:analysis; D051381:Rats; D011919:Rats, Inbred Strains; D012550:Schistosoma mansoni / Q000201:enzymology*
D006597:Fructose-Bisphosphatase; D005952:Glucose-6-Phosphatase; D010729:Phosphoenolpyruvate Carboxykinase (GTP); D011766:Pyruvate Carboxylase