A novel carbon dioxide fixation step to form oxaloacetate with subsequent reduction to malate. 36 moles of ATP formed per mol of glucose. There has been much debate about the relative importance of the three PEP- starting options in parasitic helminths. A low level of functional TCA cycle activity will contribute significantly to overall ATP production e.g. as evident in schistosomes and filarial worms. Under more aerobic conditions the same helminths may even employ a functional TCA cycle i.e. some helminths may have both aerobic and anaerobic mitochondria for flexibility.
Parasitic protozoa have many adaptations in energy metabolism.
For example, bloodstream forms of trypanosomes have an aerobic glycolytic pathway involving a specialised organelle called the glycosome, while trichomonads can synthesis ATP in a unique hydrogenosome organelle. The anaerobic protozoa, Entamoeba utilises novel thiol compounds in glucose metabolism. Anaerobic protozoa do not have mitochondria and do not contain the usual electron transport proteins found in parasites but low redox potential iron-sulphur compounds. In conclusion it is apparent parasites have diverse and sometimes unique adaptations in energy metabolism.