The oxidative metabolism of Ascaris suis

Abstract

The oxidative metabolism of A. suis has been studied manometrically on whole worms and muscle pulp. Ascaris is considered to be an aerobic organism with small O2 requirement. The O2 uptake rises with increasing O2 tension. Prolonged anaerobiosis causes an O2 debt. The low O2 requirement and uptake seem to be conditioned by, or to have conditioned, a system particularly adapted to allow low rates of oxidation only. To this end the following factors contribute in addition to the low O2 tension in the intestine of the host:[long dash]1) a low conc. of cytochrome in spite of the presence of succinic dehydrogenase, 2) a low conc. of catalase, 3) the apparent inability of the worm to deal with accumulated oxaloacetic acid, which decreases the activity of succinic dehydrogenase. Every rise of the O2 uptake, whether caused by the addition of methylene blue or by an increase of the O2 tension, is accompanied by the formation of H2O2 which is not rapidly decomposed, owing to the very low conc. of catalase. Worms brought into an atmosphere of 100% O2 develop a strong spasm and die within 1/2-1 hr. H2O2 is formed and assumed to be the cause of death. In O2 hypertension, oxyhemoglobin is oxidized by H2O2 to methemoglobin. This can act as a weak peroxidase. It is thought possible that small amts. of H2O2, if formed even at low oxidation rates and low O2 tension, may be eliminated by secondary peroxidatic oxidation reactions catalyzed by methemoglobin.