title: Dephosphorylation of distinct sites in myosin light chain by two types of phosphatase in aortic smooth muscle.
abstract: Two types of myosin light chain phosphatase from aortic smooth muscle extract were separated by chromatography on heparin-agarose. The phosphatase which appeared in the flow-through fractions had low activity on actomyosin, its apparent molecular mass was 260 kDa and upon ethanol treatment it generated a catalytic subunit with an apparent molecular mass of 36-39 kDa as determined by gel filtration. This phosphatase preferentially dephosphorylated the alpha-subunit of phosphorylase kinase and its phosphorylase phosphatase activity was not inhibited by heparin, inhibitor-1 or inhibitor-2. The phosphatase retained by heparin-agarose had high activity on actomyosin, its apparent molecular mass was 150 kDa and upon ethanol treatment it generated a catalytic subunit with an apparent molecular mass of 39-42 kDa. It preferentially dephosphorylated the beta-subunit of phosphorylase kinase and its phosphorylase phosphatase activity was not inhibited by heparin, inhibitor-1 or inhibitor-2. Myosin light chain was phosphorylated by myosin light chain kinase in peptides AB (Ser-P) and CD (Thr-P), and/or by protein kinase C in peptides E (Ser-P) and F (Thr-P) as determined by one-dimensional phosphopeptide mapping. The catalytic subunit of heparin-agarose flow-through phosphatase preferentially dephosphorylated peptide F over peptides AB, CD and E in both isolated light chain and actomyosin. The catalytic subunit of heparin-agarose bound phosphatase could effectively dephosphorylate all sites in isolated light chain, whereas it was less effective on dephosphorylation of peptide E in actomyosin.
authors.affiliation: Department of Biological Chemistry, College of Medicine, University ofIllinois Chicago.
authors.forename: F
authors.initials: F
authors.lastname: Erdödi
authors.forename: A
authors.initials: A
authors.lastname: Rokolya
authors.forename: M
authors.initials: M
authors.lastname: Bárány
authors.forename: K
authors.initials: K
authors.lastname: Bárány
mesh_terms: D000818:Animals; D001011:Aorta / Q000201:enzymology; D002352:Carrier Proteins; D002845:Chromatography; D002850:Chromatography, Gel; D006493:Heparin / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D008970:Molecular Weight; D009131:Muscle, Smooth, Vascular / Q000201:enzymology*; D043263:Myosin-Light-Chain Phosphatase; D009218:Myosins / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D010764:Phosphorylase Kinase / Q000378:metabolism; D010766:Phosphorylation; D011506:Proteins / Q000494:pharmacology; D013552:Swine; D000097847:Protein Phosphatase Inhibitory Proteins
chemical_list: D002352:Carrier Proteins; D006493:Heparin; D047908:Intracellular Signaling Peptides and Proteins; D043263:Myosin-Light-Chain Phosphatase; D009218:Myosins; D010749:Phosphoprotein Phosphatases; D010764:Phosphorylase Kinase; D011506:Proteins; C021042:protein phosphatase inhibitor-1; C024833:protein phosphatase inhibitor-2; D000097847:Protein Phosphatase Inhibitory Proteins