title: In vitro enzyme activation with calbindin-D28k, the vitamin D-dependent 28 kDa calcium binding protein.
abstract: Purified porcine erythrocyte membrane Ca(2+)-ATPase and 3':5'-cyclic nucleotide phosphodiesterase were stimulated in a dose-dependent, saturable manner with the vitamin D-dependent calcium binding protein from rat kidney, calbindin-D28k (CaBP-D28k). The concentration of CaBP-D28k required for half-maximal activation (K0.5 act.) of the Ca(2+)-ATPase was 28 nM compared to 2.2 nM for calmodulin (CaM), with maximal activation equivalent upon addition of either excess CaM or CaBP-D28k. 3':5'-Cyclic nucleotide phosphodiesterase (PDE) also showed equivalent maximum saturable activation by calbindin (K0.5 act. = 90 nM) or calmodulin (K0.5 act. = 1.2 nM). CaBP-D28k was shown to effectively compete with CaM-Sepharose for PDE binding. Immunoprecipitation with CaBP-D28k antiserum completely inhibited calbindin-mediated activation of PDE but had no effect on calmodulin's ability to activate PDE. While the physiological significance of these results remains to be established, they do suggest that CaBP-D28k can activate enzymes and may be a regulator of yet to be identified target enzymes in certain tissues.
authors.affiliation: Department of Biochemistry, University of Kentucky College of Medicine, Lexington.
authors.forename: P D
authors.initials: PD
authors.lastname: Reisner
authors.forename: S
authors.initials: S
authors.lastname: Christakos
authors.forename: T C
authors.initials: TC
authors.lastname: Vanaman
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism*; D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology; D064092:Calbindin 1; D064026:Calbindins; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D002417:Cattle; D004789:Enzyme Activation; D004910:Erythrocyte Membrane / Q000201:enzymology; D007668:Kidney / Q000378:metabolism; D011233:Precipitin Tests; D051381:Rats; D064030:S100 Calcium Binding Protein G / Q000378:metabolism*
chemical_list: C576500:Calb1 protein, rat; D064092:Calbindin 1; D064026:Calbindins; D002147:Calmodulin; D064030:S100 Calcium Binding Protein G; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D000252:Calcium-Transporting ATPases