Enzymatic Phosphate Transfer in Plant Systems

Citation

Saltman, Paul David (1953) Enzymatic Phosphate Transfer in Plant Systems. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/P4DK-FW41. https://resolver.caltech.edu/CaltechETD:etd-05092003-152156

Abstract

The experiments described in this thesis have established that the same phosphorylated intermediates of carbohydrate metabolism known to occur during the course of glycolysis in yeast and muscle tissue are involved in the carbohydrate metabolism of the pea seed. In the identification of these glycolytic intermediates use has been made of chromatographic and other techniques developed for the purpose. Two enzymes of the glycolytic sequence not previously characterized in higher plants have been separated and studied. These are phosphofructokinase and hexokinase. Both of the enzymes are concerned with the direct phosphorylation of substrate with adenosine triphosphate (ATP) - a key compound in the energy metabolism of the cell. Phosphofructokinase, which catalyzes the reaction fructose-6-phosphate + ATP <-> fructose-1, 6-diphosphate + ADP has been partially purified from pea seed meal and characterized with respect to its pH optimum, inhibitors, stability, substrate affinities, and substrate specificity. A method for the assay of the enzymatic activity has bean developed in which aldolase is employed for the direct determination of fructose diphosphate formed. Hexokinase, which catalyzes the reaction hexose + ATP <-> hexose-6-phosphate + ADP has, likewise, been partially purified and characterized with respect to several of its properties. Both enzymes have been found in a variety of higher plants, indicating the ubiquity of the glycolytic sequence. Although phosphofructokinase is a soluble cytoplasmic constituent, hexokinase appears to occur both in an insoluble and in an soluble form, the distribution being dependent upon the tissue studied and the method of preparation used. The fact that the insoluble or mitochondrial fraction seems to contain the major fraction of the hexokinase activity is of interest in light of the fundamental role of the mitochondria in the generation of ATP via oxidative phosphorylation.

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