S‐Adenosyl‐L‐homocysteine hydrolase from Dictyostelium discoideum is inactivated by cAMP and reactivated by NAD⁺

Purified S-adenosyl-L-homocysteine hydrolase from Dictyostelium discoideum is inactivated when incubated at 25 degrees C with cAMP. Half maximal velocity of the inactivation process occurs at 10 microM cAMP. Catalytic activity is fully restored by further incubation with NAD+, but not with NADP+ or NADH. The enzyme must be preincubated with cAMP or NAD+ to induce inactivation or reactivation, respectively, since neither of these ligands has an effect on the active or inactive enzyme when added directly to the assay. These results suggest a role for cAMP and NAD+ in the regulation of cellular methylation reactions by altering the level of S-adenosyl-L-homocysteine via S-adenosyl-L-homocysteine hydrolase.