Characterization of ATP-stimulated guanylate cyclase activation in rat lung membranes

Abstract

Many of the effects of ANP are mediated through the elevation of cellular cGMP levels by the activation of particulate guanylate cyclase. While the stimulation of this enzyme is receptor-mediated, the molecular mechanism of activation remains unknown. In this study we present evidence that ATP as well as its analogues adenosine-5′- O-(3-thiotriphosphate) (ATPγS) and adenylylimidophosphate (AMPPNP) activates guanylate cyclase from rat lung membranes and markedly potentiates the effect of ANP on the enzyme. The order of potency is ATP γS > ATP > AMPPNP. The enzyme activation by adenine nucleotide and ANP together is much more than the sum of the individual activations, suggesting that ATP may be the physiological component essential for the ANP-stimulated guanylate cyclase activation. The ATPγS-stimulated guanylate cyclase activity diminishes in the presence of various kinds of detergents, suggesting either that the conformation of an ATP binding site in guanylate cyclase is altered by detergents or that protein-protein interaction may be involved in the activation of guanylate cyclase by ATP. Guanylate cyclase from rat lung membranes is poorly activated by ANP and/or ATPγS after removing the cytosolic and weakly membrane-associated proteins or factors by centrifugation. Pre-incubation of the membranes with ATPγS retains enzyme activation after membrane washing. These results suggest either that ATPγS stabilizes the conformation of nucleotide binding site in guanylate cyclase from denaturation by membrane washing, or that the stimulatory effect of ATP on guanylate cyclase activity may be mediated by accessory proteins or non-protein cofactors which are lost during membrane washing, but remain bound to membranes by ATPγS pretreatment.