This work discusses the regulation of glycogen metabolism in Dictyostelium discoideum during its developmental cycle. Specifically, the possible cAMP dependent regulation of glycogen phosphorylase and glycogen synthase was examined. In other systems, cAMP can regulate at the level of the gene (procaryotes, CAP protein) or at the level of covalent, reversible modification of the enzyme activity (eucaryotes, cAMP-dependent protein kinase-cAMPdPK). In Dictyostelium, glycogen phosphorylase and glycogen synthase have each been found to occur in two forms; one regulated allosterically and the other independent of allosteric regulation.
The regulation of the two forms of glycogen phosphorylase was examined in single-cell suspensions to which cAMP or one of several cAMP analogs were added to mimic differentiative conditions. The allosterically regulated form of glycogen phosphorylase, phosphorylase b, decreased in the presence of cAMP while a corresponding increase in phosphorylase a, the non-allosterically regulated form of glycogen phosphorylase, was observed over an 8 hr period in the same cultures. In the presence of cAMP analogs, a similar time course of regulation for the two forms of glycogen phosphorylase occurred but only 2’deoxy-cAMP gave an effect comparable to cAMP. Under these same conditions, northern blot analysis of three developmentally regulated mRNAs--PL3, D11, and D3--revealed that normal gene regulation was occurring. Under conditions where elevation of intracellular cAMP was inhibited, neither regulation of phosphorylase enzyme activity nor of the 3 genes was observed. This indicated that under these conditions intracellular elevation of cAMP was necessary for the observed effects on enzyme and gene activity. This requirement for intracellular cAMP may indicate the involvement of a cAMPdPK.
The properties of a phosphorylase b kinase found in amoebal extracts are described. The kinase activity coeluted with the phosphorylase b activity on a DE·52 anion exchange column. Under the conditions described conversion of the phosphorylase b activity to the phosphorylase a activity was observed. However, an increase in molecular weight to 104 kd (as seen for purified phosphorylase a) was not observed.
The characterization of a partially purified glycogen synthase I and its developmental regulation are described. Also described are in vitro attempts to convert the I form to the allosterically regulated, D form, under conditions conducive to phosphorylation. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/53916 |
| Date | January 1988 |
| Creators | Brickey, Debra A. |
| Contributors | Biology, Rutherford, Charles L., Krieg, Noel R., Esen, Asim, Benoit, Robert E., Ebel, Richard E. |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | x, 101 leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 19730856 |
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