CO(2)-fixing enzymes during moulting from third larval to fourth larval stage of Anisakis simplex and Hysterothylacium aduncum (Nematoda: Anisakidae).

The fixing of CO(2) is an important metabolic process for many organisms. In the anisakid nematodes, CO(2) has been shown to be necessary for their development, at least in vitro. The presence of CO(2) stimulates the moulting (M3) of the larvae from the third (L3) to the fourth (L4) stage and prolongs the survival, at least, in vitro. We determined the activity of CO(2)-fixing enzymes, common to many organisms, in two anisakids: Anisakis simplex, a parasite of cetaceans, and Hysterothylacium aduncum, a parasite of fish. Although no activity was detected for pyruvate carboxylase or carboxylating-malic enzyme, we detected phosphoenolpyruvate carboxykinase (PEPCK) and phosphoenolpyruvate carboxylase (PEPC) activity. In A. simplex, PEPCK was clearly higher than that of PEPC throughout the moulting process studied. In H. aduncum, although the activity of both enzymes was of similar magnitude, they showed different behaviour; PEPCK activity decreased after the moulting to L4, PEPC activity increased so that the ratio PEPCK/PEPC activity decreased from 1.90 before moulting to 0.59 after.