title: Phosphorylation of smooth muscle myosin light chain kinase by Ca2+-activated, phospholipid-dependent protein kinase.
abstract: Protein kinase C incorporates phosphate into two sites of myosin light chain kinase (MLC-kinase) in the absence of calmodulin. Phosphorylation is all but abolished in the presence of Ca2+ and calmodulin, suggesting that both sites of phosphorylation are close to the calmodulin binding site. The phosphorylation of MLC-kinase results in an approximately 10-fold increase in the dissociation constant of MLC-kinase for calmodulin. Following phosphorylation (2 mol/mol of enzyme) of MLC-kinase by protein kinase C, an additional 2 mol of phosphate can be incorporated into the MLC-kinase apoenzyme by the cAMP-dependent protein kinase. Different maps of phosphopeptides were obtained by tryptic hydrolysis from MLC-kinase preparations phosphorylated by each kinase. The phosphorylation sites for the cAMP-dependent kinase were located in a fragment of approximately 25,000 daltons. In contrast the phosphorylation sites for protein kinase C are found in a much smaller tryptic peptide. These results suggest that the phosphorylation sites on MLC-kinase are different for protein kinase C and for cAMP-dependent protein kinase. However, phosphorylation in both regions results in a reduced affinity for calmodulin.
authors.forename: M
authors.initials: M
authors.lastname: Ikebe
authors.forename: M
authors.initials: M
authors.lastname: Inagaki
authors.forename: K
authors.initials: K
authors.lastname: Kanamaru
authors.forename: H
authors.initials: H
authors.lastname: Hidaka
mesh_terms: D000818:Animals; D001665:Binding Sites; D002147:Calmodulin / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005895:Gizzard, Avian / Q000201:enzymology; D009130:Muscle, Smooth / Q000201:enzymology*; D009219:Myosin-Light-Chain Kinase; D010446:Peptide Fragments / Q000032:analysis; D010766:Phosphorylation; D011493:Protein Kinase C; D011494:Protein Kinases / Q000378:metabolism*; D013997:Time Factors; D014357:Trypsin / Q000378:metabolism; D014422:Turkeys
chemical_list: D002147:Calmodulin; D010446:Peptide Fragments; D011494:Protein Kinases; D011493:Protein Kinase C; D009219:Myosin-Light-Chain Kinase; D014357:Trypsin