Studies on the metabolism of the Protozoa. 3. Metabolism of the ciliate Tetrahymena pyriformis (Glaucoma piriformis)

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Abstract
T. pyriformis maintains metabolism and motility in the absence of extracellular nutrients for considerable periods at room temp. or at 37[degree]. Under aerobic conditions at 37[degree] the ciliate respires with a g02 of 480 and an R. Q. of 0.85. This endogenous respiration is practically independent of the intracellular glycogen, only slightly stimulated by the addition of glucose and a number of dicarboxylic acids, but almost doubled by 0.01 [image]. acetate, propionate or butyrate. High concns. of azide or 2,4-dinitrophenol inhibit endogenous respiration, but low concns. stimulate it; in all cases they reduce motility. The cytochrome system of the ciliate is composed of cytochromes b, c and e, but very little a; homogenates display no cytochrome oxidase activity towards p-phenylenediamine. Respiration of the ciliate is comparatively resistant to cyanide and CO. T. pyriformis contains a heat-labile peroxidase (purpurogallin number, 0.033); in the presence of H2O2 it oxidizes phenolic compounds and reduced cytochrome c. Anaerobic metabolism and motility depend on the fermentation of the intracellular glycogen; in the absence of extraneous carbohydrate the ciliate produces large amts. of succinic acid, with smaller quantities of lactic and acetic acid, and assimilates some CO2. Cell-free, centrifuged homogenates contain enzymes capable of hydrolyzing starch, glycogen and maltose to glucose; they also phosphorylate glycogen and starch to form glucose -1 -phosphate and contain phosphoglucomutase and oxoisomerase. Cell-free prepns. convert fructose-l,6-diphosphate to triosephosphate, which is fermented to lactic acid. The process is stimulated by arsenate and inhibited by iodoacetate. Homogenates of the ciliate display both succinic and lactic dehydrogenase activity; in the presence of atmospheric O2, they oxidize lactic, but not succinic, acid.
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