A comparison of the membrane-bound and extracellular cyclic AMP phosphodiesterases of Dictyostelium discoideum |
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Authors: | Renée I. Shapiro Jakob Franke Elizabeth J. Luna Richard H. Kessin |
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Affiliation: | Department of Cellular and Development Biology, The Biological Laboratories, Harvard Universty, 16 Divinity Avenue, Cambridge, MA 02138 U.S.A. |
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Abstract: | The Dictyostelium discoideum membrane-bound and extracellular cyclic nucleotide phosphodiesterases (EC 3.1.4.17) shear several properties including the ability to react with a specific glycoprotein inhibitor and small inhibitory molecules. We have partialy purified the membrane-bound enzyme and compared its properties to those of the extracellular form. The kinetic properties of the two forms were similar except that, while associated with membrane particles, the membrane-bound form exhibited non-linear kinetics when assayed ove a broad substrate range. The isoelectric point of the membrane-bound phosphodiesterase was identical to that of the extracellular enzyme when isoelectrofocusing was done in the presence of 6 M urea. The molecular weights of membrane-bound and extracellular enzyme, determined by gel filtration, were the same following isoelectrofocusing in the presence of 6 M urea. When precipitated with an antiserum prepared against purified extracellular phosphodiesterase, the partially purified membrane-bound enzyme preparation was shown to contain a Mr 50 000 polypeptide comigrating with the extracellular enzyme during SDS polyacrylamide gel electrophoresis. When the iodinated extracellular enzyme and the iodinated Mr 50 000 polypeptide from membrane-bound enzyme were subjected to partial proteolytic digestion, similar profiles were obtained indicating extensive regions of homology. |
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Keywords: | cyclic AMP Phosphodiesterase (D. discoideum) |
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