Studies on the metabolism of the protozoa. 5. Metabolism of the parasitic flagellate Trichomonas foetus

Abstract

The parasitic flagellate Trichomonas foetus can maintain metabolism and motility in the absence of extra-cellular nutrients for considerable periods at 37[degree] under both aerobic and anaerobic conditions; this endogenous metabolism depends on the fermentation of intracellular glycogen. Under aerobic conditions, the parasite respires with a qo2 of about 176 at 37[degree]. This O2 uptake is doubled in the presence of either glucose, fructose or mannose, and is considerably stimulated by both galactose and lactose, while maltose, sucrose, glutamate and glutamine give small respiratory stimulations. Respiration of the flagellate is probably independent of cytochrome pigments; no evidence for the presence of cytochromes could be obtained by spectroscopic examination, by the use of respiratory inhibitors, or by the use of cell homogenates with p-phenylenediamine. T. foetus shows vigorous catalatic activity; T. vaginalis and T. gallinae do not contain catalase. At pH 5.5 0.04 [image] arsenite or 0.01 [image] azide appreciably stimulate the endogenous respiration of T. foetus, but at the same time abolish cellular motility. Under anaerobic conditions, endogenous metabolism takes place with a qN2 of 325; this fermentation is 88% inhibited by CO200003 [image] iodo-acetate, but is relatively insensitive to other inhibitors tested. Intracellular glycogen disappears on incubation under aerobic or anaerobic conditions in the absence of extracellular substrate; in the presence of glucose, fructose, lactose or galactose, although 02 uptake or CO2 output is considerably increased, there is a net synthesis of glycogen; maltose exerts a slight sparing action on the utilization of intracellular glycogen. Under aerobic or anaerobic conditions, glycogen is fermented to a mixture of succinic and acetic acids; there is a net formation or assimilation of CO2 depending on the conditions, and a gas other than CO2 is produced. Glycogen breakdown and succinic acid production are favored by anaerobic conditions and the presence of CO2 in the gas phase. Cell-free preparations contain amylase, maltase, phosphorylase, hexokinase, phosphoglucomutase and ketoisomerase, aldolase and a triose phosphate oxidizing system. The activity of aldolase can be inhibited by as much as 75% in the presence of 0.005 [image] 2:2''-dipyridyl.