title: Calmodulin inhibits the phosphorylation of spectrin in vitro.
abstract: In vitro phosphorylation of purified spectrin dimer was studied in the presence of Ca2+-calmodulin (CaM). CaM inhibited autophosphorylation of the beta subunit of spectrin. The inhibitory effect (65% at a 32-fold molar excess) appeared to be due to a weak interaction of CaM with spectrin. CaM was similarly effective in a phosphatase-stimulated autothiophosphorylation of the beta subunit with [gamma-35S]ATP. Hence, its inhibitory effect was not due to stimulation of a spectrin-associated phosphatase activity. Phosphorylation of spectrin by the catalytic subunit of a cAMP-dependent protein kinase occurred in both subunits (1984, FEBS Lett. 169, 323). CaM selectively inhibited a cAMP-dependent phosphorylation of the alpha subunit of spectrin to 30% at two CaM per spectrin. It was ineffective on the cAMP-dependent phosphorylation of the beta subunit up to a 32-fold molar excess. These results yield functional evidence for a CaM-spectrin interaction. They further suggest that CaM can regulate the extent of a cAMP-dependent phosphorylation of the alpha subunit of spectrin.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000469:Alkaline Phosphatase / Q000097:blood; D002147:Calmodulin / Q000378:metabolism*; D002384:Catalysis; D000242:Cyclic AMP / Q000502:physiology; D004591:Electrophoresis, Polyacrylamide Gel; D004910:Erythrocyte Membrane / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D010766:Phosphorylation; D011494:Protein Kinases / Q000097:blood; D013049:Spectrin / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D013049:Spectrin; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D011494:Protein Kinases; D000469:Alkaline Phosphatase