Calmodulin-dependent high-affinity cyclic AMP phosphodiesterase in liver membranes

Plasma membranes from hamster liver were prepared by differential and continuous sucrose gradient centrifugation. The membranes contained a low K_m cyclic AMP phosphodiesterase (EC 3.5. lc) and calmodulin. The activity of the membrane phospho-diesterase was reduced with EGTA and LaCl₃. The membrane low K_m cyclic AMP phosphodiesterase was solubilized with Triton X-100 and then chromatographed on DEAE-cellulose to remove calmodulin. After elution, phosphodiesterase was stimulated with exogenous calmodulin; this activation was blocked with EGTA. Thus a low K_m cyclic AMP phosphodiesterase has been shown to be dependent on calmodulin for “maximal” activity.