Kinase activity associated with caldesmon is Ca2+/calmodulin-dependent kinase II.
The relationship of the kinase which co-purifies with caldesmon to Ca2+/calmodulin-dependent protein kinase II (CaM-kinase II) was investigated by studying the phosphorylation of bovine brain synapsin I, as well-characterized substrate of CaM-kinase II. Synapsin I is a very good substrate (Km = 90 nM) of the co-purifying kinase, which phosphorylates two sites in synapsin I, both of which are distinct from the single site phosphorylated by cyclic-AMP-dependent protein kinase. Phosphorylation of synapsin I is Ca2(+)- and calmodulin-dependent: half-maximal activation occurs at 0.13 microM-Ca2+ and maximal activity at 0.4 microM-Ca2+. Phosphorylation of the co-purifying kinase slightly enhances the rate, but does not alter the stoichiometry, of subsequent synapsin I phosphorylation; it does, however, circumvent the requirement for Ca2+ and calmodulin. The properties of this kinase therefore closely resemble those of CaM-kinase II, and we conclude that it is probably a smooth-muscle isoenzyme of CaM-kinase II.
Scott-Woo
G C
GC
Department of Medical Biochemistry, Faculty of Medicine, University of Calgary, Alberta, Canada.
Sutherland
C
C
Walsh
M P
MP
D000818:Animals; D001921:Brain / Q000201:enzymology; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D002417:Cattle; D002645:Chickens; D005895:Gizzard, Avian / Q000201:enzymology; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010449:Peptide Mapping; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D016704:Synapsins
D002148:Calmodulin-Binding Proteins; D009419:Nerve Tissue Proteins; D016704:Synapsins; D010770:Phosphotransferases; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases