The Anaerobic Incorporation of ³²P into Adenosine Triphosphate by Hymenolepis diminuta

Abstract

The anaerobic incorporation of ³²P into ATP by the tapeworm Hymenolepis diminuta was studied in the presence and absence of uncouplers of oxidative phosphorylation and anticestodal agents. Low concentrations of all compounds tested inhibited this incorporation. Under the anaerobic conditions employed, internal ATP concentrations remained constant in spite of the inhibition of the incorporation of exogenous ³²P into ATP. On the other hand, removal of carbon dioxide, which is required by the helminths for optimal anaerobic carbohydrate utilization, produced a marked decrease in both ³²P incorporation and ATP levels. These findings indicate the presence of an anaerobic phosphorylation site associated with electron transport. Mitochondrial preparations obtained from H. diminuta rapidly exchange ³²P into ATP upon incubation in the absence of exogenous substrates. This exchange reaction is inhibited also by uncouplers and anticestodal agents. In addition, fumarate was reduced by NADH in aged or partially disrupted mitochondria of the worm, and no cytochrome oxidase activity was demonstrable.