Platelet and leucocyte calmodulins: isolation and characterisation.

The calcium-dependent regulatory proteins, calmodulins, have been isolated from human blood platelets and guinea pig peritoneal polymorphonuclear leucocytes using the urea methanol procedure of Grand et al. [Biochem. J. 177, 521-529 (1978)]. The calmodulins were purified to homogeneity as indicated by polyacrylamide gel electrophoresis and both proteins comigrated with bovine brain calmodulin with mobilities corresponding to molecular weights of 16 000-17 000. The yield of calmodulin from platelets was higher on a wet weight basis than the yield from leucocytes but the former compared favourably with yields reported for brain and other tissues. Both calmodulin preparations significantly stimulated brain cyclic nucleotide phosphodiesterase, erythrocyte ghost Ca2+ ATPase and platelet phosphorylase kinase activities at the microgram level. Stimulation of Lubrol-solubilised brain adenylate cyclase was only marginally significant with platelet calmodulin and rarely demonstrable with the leucocyte preparations. Although biological activities of both proteins were retained during storage at -20 degrees C, higher-molecular-weight aggregates slowly formed which could not be dissociated during dodecylsulphate/mercaptoethanol denaturation.