Studies on the metabolism of the protozoa. 4. Metabolism of the parasitic flagellate Strigomonas oncopelti

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Abstract
The parasitic flagellate Strigomonas oncopelti can respire and maintain motility under aerobic conditions for several hours in the absence of extracellular substrates. This respiration takes place with a qO2 of about 146 at 30[degree] and an R.Q. of 0.9. Respiration of the flagellate is considerably stimulated by glucose, fructose, mannose, L-glutamate, glutamine, succinate, alpha-oxoglutarate, DL-aspartate, asparagine and lactate while DL - alanine, ethanol, glycerol, galactose, lactose, sucrose and maltose stimulate respiration to a lesser extent. Citrate, pyruvate and short-chain fatty acids either have no effect or produce a small inhibition of respiration. Respiration of S. oncopelti is mediated to a large extent by the cytochrome system. Cytochromes a,b and c have been demonstrated spectroscopically, and cytochrome oxidase and succinic oxidase activity has been shown in cell homogenates. Respiration, and to a lesser extent motility, is quite sensitive to cyanide, azide and 2:4-dinitrophenol. Under anaerobic conditions, metabolism and motility depend on the availability of utilizable extracellular carbohydrate: in a Ringer-bicarbonate medium in the presence of glucose, qN2 values CO2 of up to 800 have been observed. This fermentation is appreciably inhibited by 2:2''-dipyridyl. Under both aerobic and anaerobic conditions, glucose is degraded to a mixture of ethanol, glycerol, succinic and pyruvic acids and CO2. Using homogenates of S. oncopelti, the flagellate has been shown to contain hexokinase, phosphoglucomutase and ketoisomerase, aldolase, a triose phos-phate oxidizing system, carboxylase, succinic, lactic and malic dehydrogenases and fumarase.
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