ABSTRACT
20Parasitic helminths are a very heterogeneous group of organisms, but they all have a large capacity for anaerobic functioning at some stage of their development. In the various stages of their life cycle, parasites have to adapt to different environments; the availability of external food and oxygen varies widely. These variations in the external conditions influence the energy metabolism of parasitic helminths.
In general, free-living stages have an aerobic energy metabolism, whereas parasitic stages have an anaerobic one. The transitions from aerobic to anaerobic energy metabolism are rather unique because, unlike the temporary anaerobiosis occurring in other animals, in parasitic helminths the resulting anaerobic energy metabolism is permanent. The same organism will never switch back to its previous aerobic metabolism; only its offspring will. In this respect the metabolic transition from aerobic to anaerobic is different from that occurring in any other organism discussed in this book, although the anaerobic pathways themselves are comparable. Details on cytosolic and mitochondrial processes in the energy metabolism of various parasitic helminths will be reviewed. Furthermore, possible mechanisms of the aerobic/anaerobic transitions and short-term changes as well as long-term adaptations to anoxic functioning will be discussed.
