Studies on the metabolism of the Protozoa. 1. Metabolism of the parasitic flagellate, Trypanosoma lewisi

Abstract

The motility and metabolism of T. lewisi can be maintained in vitro both aerobically and anaerobically in the presence of suitable extracellular nutrients. Its respiration depends on the cytochrome system. It is very sensitive to cyanide and is also inhibited by CO, the latter reaction being light-reversible. In the absence of extracellular nutrients. T. lewisi takes up O2 at a rate of 40 [mu]l. of O2 per mg. of cellular N (or about 109 cells) in 1 hr. at 37[degree]. In the presence of added glucose, mannose, fructose or glutamine, the qO2 value increases from 40 to 600 or more. Glycerol, asparagine and glutamic acid increase the O2 uptake to a smaller extent. Glucose is oxidized with an R.Q. of 0.97. For each molecule utilized aerobically, 3-4 mol. O2 are taken up, and 1 mol. equivalent of organic acid is produced, half of this being acetic acid, and the rest mainly succinic and lactic acids. Substances not utilized aerobically include: galactose, sorbose, xylose, sucrose, lactose, maltose, lactate, pyruvate, succinate, citrate, alpha-ketoglutarate, acetate, formate, glycine, alanine and aspartic acid. Added lactate and succinate were not oxidized by intact cells, but lactic and succinic dehydrogenases could be demonstrated in cell homogenates. Anaerobically, T. lewisi ferments glucose, the reaction being accelerated 3-fold by 0.02 [image] pyruvate, and 12-fold by 0.016 [image] bicarbonate. The max. rate observed in the presence of CO2 was [image] For each mol. of glucose utilized anaerobically, 0.74 mol. of CO2 are fixed, and 2.5 mol. equivalents of organic acid are produced. The bulk of the acid accumulating anaerobically is succinic acid (70%) and lactic acid (15%); the rest is pyruvic and acetic acid. Anaerobic fermentation is very sensitive to metal-binding substances, being inhibited by about 75% by 0.0003 [image] 2,2[image]-dipyridyl and 8-hydroxyquinoline.