Abstract
Adenylate cyclase activity in isolated rat liver plasma membranes was inhibited by NADH in a concentration-dependent manner. Half-maximal inhibition of adenylate cyclase was observed at 120 μM concentration of NADH. The effect of NADH was specific since adenylate cyclase activity was not altered by NAD +, NADP +, NADPH, and nicotinic acid. The ability of NADH to inhibit adenylate cyclase was not altered when the enzyme was stimulated by activating the G s regulatory element with either glucagon or cholera toxin. Similarly, inhibition of G i function by pertussis toxin treatment of membrane did not attenuate the ability of NADH to inhibit adenylate cyclase activity. Inhibition of adenylate cyclase activity to the same extent in the presence and absence of the Gpp(NH)p suggested that NADH directly affects the catalytic subunit. This notion was confirmed by the finding that NADH also inhibited solubilized adenylate cyclase in the absence of Gpp(NH)p. Kinetic analysis of the NADH-mediated inhibition suggested that NADH competes with ATP to inhibit adenylate cyclase; in the presence of NADH (1 mM) the K m ATP was increased from 0.24 ± 0.02 mM to 0.44 ± 0.08 mM high NADH concentrations to completely inhibit the enzyme suggest that NADH interacts at a site(s) on the enzyme to increase the K m for ATP by 2-fold and this inhibitory effect is overcome at high ATP concentrations.
Published Version
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