Properties and characterization of low molecular weight inhibitor of calmodulin-dependent cAMP phosphodiesterase from rat liver

We have identified two different species of inhibitors of calmodulin-dependent cAMP phosphodiesterase: 1) a low molecular weight (LMW) and 2) a high molecular weight (HMW) form. These inhibitors are extracted from rat liver. Both LMW and HMW inhibitors are heat-stable, acidic in nature and lose activity with prolonged storage and/or repeated freezing and thawing. The low molecular weight inhibitor has been purified to about 7,000-fold with 300% recovery. LMW inhibits calmodulin-dependent cAMP phosphodiesterase regardless of the source of calmodulin (e.g. fat, brain, heart, erythrocytes). LMW appears to be lipid in nature with a molecular weight of 1,500-5,000. The role of these inhibitors in diabetes and mechanism of action of insulin is presented.