title: Comparison of calmodulin binding to brain synaptic and coated vesicles.
abstract: Several characteristics of calmodulin association with brain synaptic and coated vesicles wer analyzed and compared. Radioimmunoassay revealed that both classes of vesicles contain approx. 1 microgram of calmodulin per mg of vesicle protein. Discontinuous sucrose gradients revealed that coated and synaptic vesicles preparations were homogeneous and had different sedimentation properties. Binding of 125I-labeled calmodulin to sympatic and coated vesicles was Ca2+ dependent and displaced by unlabeled calmodulin but not by troponin-C. Scatchard analysis revealed the presence of two binding sites. In both vesicle types there was one high-affinity, low-binding-capacity site (Kd = 1-39 nM and Bmax = 4-16 pmol/mg) and one low-affinity, high-binding-capacity site (Kd = 102-177 nM and Bmax = 151-202 pmol/mg). (Ca2+ +Mg2+)-ATPase activity was stimulated in both synaptic and coated vesicles by calmodulin. Thus synaptic and coated vesicles may possess similar calmodulin binding sites.
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D002417:Cattle; D002499:Centrifugation, Density Gradient; D008854:Microscopy, Electron; D009940:Organoids / Q000378:metabolism*; D011863:Radioimmunoassay; D013572:Synaptic Vesicles / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium