TRANSFERRIN AND FERRITIN MODULATE THE ACTIVITY OF BRAIN CALCIUM-CALMODULIN-DEPENDENT PHOSPHODIESTERASE

The effect of the key iron homeostasis proteins transferrin and ferrit in on the activity of partially purified brain calcium-calmodulin-depe ndent phosphodiesterase (CaM-PDE, EC 3.4.1.17) were studied. Transferr in and ferritin were found to be potent natural activators of CaM-PDE. The key factor determining the degree of activation by these proteins is their saturation with iron: apotransferrin activated CaM-PDE 6-7-f old; iron-poor brain ferritin and liver apoferritin (taken for compari son) activated the enzyme 4-5- and 2-fold, respectively. Diferric tran sferrin and iron-rich liver ferritin had no effects on the enzyme acti vity. Transferrin and ferritin (both in apo- and iron-saturated forms) did not change the activity of calmodulin-phosphodiesterase complex. The data suggest that apotransferrin and iron-poor transferrin are inv olved in the regulation of cyclic nucleotide content in nervous tissue .