Glyconeogenesis in Tetrahymena pyriformis

• Published in: The Journal of biological chemistry 1967-09, Vol.242 (18), p.4060-4066
• Main Authors: Shrago, Earl, Brech, Wolfgang, Templeton, Karen
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)95778-9

Phosphoenolpyruvate carboxykinase in the cytosol of Tetrahymena pyriformis is closely related to the high rate of glyconeogenesis in that organism, while the enzyme in the mitochondria does not show such a correlation. This finding, together with the observation of depression of phosphoenolpyruvate carboxykinase and malate dehydrogenase activities by glucose in the cytosol, indicates an extramitochondrial pathway for phosphoenolpyruvate synthesis from dicarboxylic acids which is similar to that postulated for rat liver and may, therefore, be of general metabolic significance. A change of oxygen tension which influences glyconeogenesis in Tetrahymena also has an effect on phosphoenolpyruvate carboxykinase and possibly other glyconeogenic enzymes. One factor in the repression and derepression of phosphoenolpyruvate carboxykinase was found to be related to oxygen tension and to occur independently of any carbohydrate in the growth medium. A phosphoenolpyruvate carboxylase has been identified in this organism. Although its exact metabolic significance is somewhat unclear, the enzyme may function as the primary CO 2 fixation mechanism in Tetrahymena .