CYCLIC NUCLEOTIDE METABOLISM IN ELECTROPLAX OF ELECTROPHORUS ELECTRICUS |
| |
Authors: | S. R. Childers F. L. Siegel |
| |
Affiliation: | Departments of Physiological Chemistry and Pediatrics, University of Wisconsin Center for Health Sciences, Madison, WI 53706, U.S.A. |
| |
Abstract: | Abstract— In order to describe the regulation of cyclic nucleotide metabolism in a cholinergic tissue, the properties of cyclic nucleotide phosphodiesterase were determined in electroplax of Electrophorus electricus and compared to those of mammalian brain. Electroplax phosphodiesterase was Mg2+ -dependent. localized in the soluble fraction and displayed normal linear Lineweaver-Burk kinetics ( K m: cyclic AMP. 1.4 μ m ; cyclic GMP, 0.54 μ m ). No low affinity (i.e. high K m) activity was detected. These results were correlated with comparatively low tissue levels of cyclic AMP (67 pmol/g) and cyclic GMP (3.2 pmol/g). Attempts were made to detect calcium-dependent phosphodiesterase because of the presence of large amounts of the calcium-dependent regulator protein (CDR) in electroplax, as this protein has been shown to activate brain phosphodiesterase. Assay with EGTA under a variety of conditions revealed that no calcium-dependent activity could be detected. Preparation of CDR-deficient phosphodiesterase also failed to produce calcium-dependent activity. Assay of phosphodiesterase in other cholinergic tissues revealed calcium-dependent activity in Electrophorus muscle and rat diaphragm but not in Torpedo electroplax. The results suggest that calcium-dependent activity is not a significant portion of phosphodiesterase in electroplax and indicate alternate roles for CDR in electric tissue. |
| |
Keywords: | |
|
|