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Log-phase Tetrahymena were washed and resuspended in a dilute salt solution supplemented with glucose, acetate, pyruvate, or carmine, as desired, and then incubated for 5 h. Intra- and extracellular activities of acid phosphatase, alpha-glucosidase, and ribonuclease were assayed. Extracellular activities were corrected for proteolytic degradation. The three nutritive substrates affected both the amount and pattern of extracellular enzyme release, but carmine had no effect. Intracellular activities declined early in the starvation period, but partially recovered with time, particularly alpha-glucosidase activity. Acetate reduced the decline in acid phosphatase activity; acetate and glucose enhanced the recovery of alpha-glucosidase activity; carmine had no effect on intracellular enzyme activities. Protein content changed little and was unaffected by the addition of substrates. Glycogen content increased during incubation; acetate and glucose enhanced the increase.

When a bleached strain of Euglena is maintained in a medium containing very low con centrations of phosphate, the acid phosphatase activity increases. The increase in acid phosphatase activity is prevented by Actinomycin D and by p-fluorophenylalanine (PFA), indicating that the increased activity is due to de novo synthesis of acid phosphatase. When phosphate is replenished, the acid phosphatase activity decreases to the level characteristic of uninduced cells before there is any appreciable cell division. When cell division resumes in the presence of PFA, the level of acid phosphatase activity remains approximately constant. This indicates that there are two different phosphatases: a constitutive enzyme, whose synthesis is insensitive to the presence of PFA, and an induced enzyme, whose synthesis is sensitive to PFA. These enzymes are not equally sensitive to changes in pH and in fluoride concentration, thus permitting them to be assayed individually in whole toluene-treated cells. Induced cells also acquire the ability to remove phosphate from the medium very rapidly.

The localization of induced and constitutive acid phosphatase activity in Euglena was studied by light and electron microscopy, using two different cytochemical methods. Cells grown in high phosphate medium have constitutive acid phosphatase activity in three regions: in the Golgi complex, around the paramylum bodies, and in the peri-reservoir vesicles. Cells that have formed an induced acid phosphatase by exposure to a phosphate-deficient medium have, in addition to the constitutive activity localized exactly as in the uninduced cell, a strong activity in the pellicle. The induced activity is not uniformly distributed over the pellicle, but is localized at the notch of each pellicle complex, near a group of about four fibrils and near a characteristic vesicle of the endoplasmic reticulum. In the cytostome, where fission begins during division, there is an alternation of large and small pellicle complexes, both of which have induced phosphatase activity. A similar alternation is seen over the entire pellicle of dividing cells.

1. Exposure of Astasia longa to oxygen+carbon dioxide (95:5) at atmospheric pressure leads to an inhibition of growth rate and of respiration. Growth resumes at the normal rate as soon as the oxygenation is discontinued, but respiration recovers more slowly. 2. Mitochondria prepared from cells exposed to oxygen+carbon dioxide (95:5) during growth have considerably decreased activities of succinate-cytochrome c oxidoreductase, NADH-cytochrome c oxidoreductase, succinate dehydrogenase and succinate oxidase activities as compared with mitochondria obtained from cells exposed to air+carbon dioxide (95:5). Cytochrome oxidase activity is not appreciably inhibited by exposure of the cells to 95% oxygen. 3. The mitochondrial fraction of Astasia contains rhodoquinone. The rhodoquinone concentration increases in cells exposed to 95% oxygen. The content of ergosterol-containing compounds also increases in the mitochondria of cells exposed to 95% oxygen. There is little change in the ubiquinone content of the mitochondrial fraction. The ubiquinone of Astasia appears to be ubiquinone-45.

1. Euglena cells were grown in culture media containing either 20mm-phosphate or 20mum-phosphate, with ethanol or glucose as the sole source of carbon, and gassed with either air+carbon dioxide (95:5) or oxygen+carbon dioxide (95:5) at atmospheric pressure. 2. After growth in low-phosphate medium with ethanol as substrate, the cells developed signs of oxygen toxicity, as indicated by a decreased rate of respiration, a decreased net synthesis of paramylum and a failure to resume growth on replenishment of phosphate. 3. After growth in low-phosphate medium with glucose as substrate, the signs of oxygen toxicity were less apparent. 4. During phosphate deprivation the carotenoid content of Euglena increased more than threefold. This increase was largely prevented by exposure of the cells to oxygen+carbon dioxide (95:5) during growth. Oxygenation appears to interfere with ring closure of the common carotenoid precursor. 5. Mitochondria obtained from Euglena exposed to oxygen during phosphate deprivation, i.e. when signs of oxygen toxicity were evident, had greatly decreased activities of succinate dehydrogenase, succinate-cytochrome c oxidoreductase and NADH-cytochrome c oxidoreductase, compared with mitochondria obtained from Euglena exposed to oxygen in medium containing 20mm-phosphate.