Studies of regulatory metabolism in Moniezia expansa: the role of phosphoenolpyruvate carboxykinase. |
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Authors: | C A Behm C Bryant |
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Affiliation: | Department of Zoology, Australian National University, Canberra 2600, A.C.T., Australia. |
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Abstract: | Phosphoenolpyruvate carboxykinase (PEPCK) from M. expansa has been partially purified and its behaviour in a range of different assay conditions has been determined. Different PEPCK's were found in the cytosol and mitochondria. Some kinetic parameters for each are presented. Both enzymes are activated by Mn2+; cytosolic PEPCK is also activated by Mg2+. The enzymes have pH optima in the range 6·4–7·0. They do not differ with respect to their apparent affinities for inosine and guanosine diphosphates, but the latter allows higher maximal activity. Little activity is observed with adenosine diphosphate. Adenosine and inosine triphosphates exert weak inhibitory effects on the Mn2+ activated enzymes; a much strongsr inhibition is exerted on the cytosolic enzyme when activated by Mg2+. A number of non-nucleotide compounds were tested for possible inhibitory effects with no success. The forward and back reactions catalyzed by PEPCK proceed at similar rates, suggesting that the enzyme may be readily raversible in vivo. |
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Keywords: | Cestoda metabolic regulation phosphoenolpyruvate carboxykinase Malate carbon dioxide fixation |
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