A soluble factor and GTP gamma S are required for Dictyostelium discoideum guanylate cyclase activity. |
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Authors: | C C Schulkes C D Schoen J C Arents R Van Driel |
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Institution: | E.C. Slater Institute for Biochemical Research, University of Amsterdam, Netherlands. |
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Abstract: | Amoeba of Dictyostelium discoideum show a rapid, transient cGMP synthesis in response to chemotactic stimulation. Using Mg(2+)-GTP as a substrate, guanylate cyclase (E.C. 4.6.1.2.) activity is found exclusively in the particulate fraction of Dictyostelium cells. Here we show that the activity is dependent on the presence of the non-hydrolysable GTP-analogue GTP gamma S, which itself is only a poor substrate for the enzyme under the prevailing conditions. Evidence is presented that a transient exposure of the enzyme to GTP gamma S is sufficient to constitutively activate the enzyme. GTP gamma S-dependent activity is found to require a factor that can be separated from the enzyme by washing the particulate fraction with low salt buffer. Addition of the soluble cell fraction to these washed membranes restores enzyme activity. |
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