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The catecholamine-responsive adenylate cyclase system and its modification by 5'guanylylimidodiphosphate
Advances in Cyclic Nucleotide Research
|January 1, 1975
Summary
Frog erythrocyte adenylate cyclase activity is enhanced by isoproterenol and Gpp(NH)p, forming a persistent active state. This hormone-facilitated activation suggests the hormone may not be continuously required for the non-hydrolyzable GTP analog.
Area of Science:
- Biochemistry
- Cellular Signaling
- Enzymology
Background:
- Adenylate cyclase systems mediate cellular responses to hormones.
- The frog erythrocyte system is a model for studying G protein-coupled receptor signaling.
Purpose of the Study:
- To investigate the role of phospholipids in frog erythrocyte adenylate cyclase activity.
- To elucidate the mechanism of activation of adenylate cyclase by catecholamines and guanine nucleotides.
Main Methods:
- Enzyme assays measuring adenylate cyclase activity in frog erythrocyte membranes.
- Preincubation experiments with agonists, nucleotides, and inhibitors.
- Effect of phospholipids and lipid extracts on enzyme activity.
Main Results:
- Acidic phospholipids inhibited adenylate cyclase.
- Isoproterenol plus Gpp(NH)p induced a persistent active state, independent of ATP and Mg++.
- Propranolol blocked Gpp(NH)p plus isoproterenol activation if added before, but not after, preincubation.
Conclusions:
- Hormone (isoproterenol) facilitates Gpp(NH)p action, potentially playing a transient role.
- Continuous hormone presence may be necessary for natural GTP activation to maintain the regulatory site.