Changes in Beta-Oxidation and Related Enzymes during the Life Cycle of Strongyloides ratti (Nematoda)

Specific activities of β-oxidation and tricarboxylic acid cycle enzymes, and enzymes related to glycolysis and glycogenesis, were determined in parasitic females of Strongyloides ratti, the first-stage larvae produced by these females, free-living adults, and free-living infective larvae. All β-oxidation and tricarboxylic acid cycle enzymes were present in infective larvae and free-living adults, which actively metabolized absorbed U-14C-palmitic acid. Palmityl-CoA synthase and NAD-dependent isocitrate dehydrogenase were not detectable in parasitic females, which oxidized palmitic acid at a low rate, if at all. NAD-dependent isocitrate dehydrogenase was not found in first-stage larvae. The ratios, phosphoenolpyruvate carboxykinase:pyruvate kinase, and phosphoenolpyruvate carboxykinase:lactate dehydrogenase were high in parasitic females, and low in other stages of the life cycle. The results suggest that the energy metabolism of the parasitic females is anaerobic. The enzymatic constitution of first-stage larvae resembles that of the parasitic females in important respects. This first stage seems to be one of enzymatic and metabolic transition between the parasitic and free-living stages.