Functional modulation of ANF-sensitive particulate guanylate cyclase by redox mechanisms

We examined the effects of sulfhydryl-reactive redox agents and of the apparent oxidation-reduction (redox) potential of the assay medium on enzyme activity and atrial natriuretic factor (ANF) binding properties of particulate cyclase from bovine adrenal cortex. Redox potential was varied by addition of redox-reactive agents and quantified by electrochemical measurement. The modification of free SH groups by thiol-reactive agents had only a minor effect on ANF binding or on the extent of ANF-dependent enzyme stimulation whereas free thiol groups were essential for basal enzyme activity on ANF-sensitive particulate guanylate cyclase. Basal and ANF-stimulated particulate guanylate cyclase activity was modulated by exposure to different redox potential states. This modulation was different for the substrates Mg · GTP and Mn · GTP. The apparent redox potential had no influence on the extent of guanylate cyclase activation by ANF. Our results suggest that critical free thiol groups, which are sensitive to thiol-reactive redo agents, are involved in the catalytic, but not in the receptor function of ANF-sensitive particulate guanylate cyclase. These thiol groups could be the structural basis for the effects of redox events which modulate basal enzyme activity, but not activation by ANF.