Calponin phosphatase from smooth muscle: a possible role of type 1 protein phosphatase in smooth muscle relaxation.
Smooth muscle myosin bound phosphatase (MBP) purified from chicken gizzard, which is a holoenzyme of type 1 delta protein phosphatase and dephosphorylated intact myosin, catalyzed the dephosphorylation of calponin phosphorylated by protein kinase C (PK-C). The Km of MBP for calponin was 0.6 microM and the Vmax was 350 nmol/min/mg. All of the multiple sites of phosphorylation by PK-C of calponin were completely dephosphorylated by MBP. Functionally, calponin dephosphorylated by MBP recovered its inhibitory effect on the actin-activated Mg(2+)-ATPase activity of myosin. Therefore, these results suggest that a type 1 delta protein phosphatase causes relaxation of smooth muscle by the dephosphorylation not only of myosin but also of calponin.
1st Department of Internal Medicine, Mie University School of Medicine, Japan.
K
K
Ichikawa
M
M
Ito
S
S
Okubo
T
T
Konishi
T
T
Nakano
T
T
Mino
F
F
Nakamura
M
M
Naka
T
T
Tanaka
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002645:Chickens; D005895:Gizzard, Avian; D007700:Kinetics; D008840:Microfilament Proteins; D009124:Muscle Proteins / Q000378:metabolism*; D009126:Muscle Relaxation; D009130:Muscle, Smooth / Q000201:enzymology*; D043263:Myosin-Light-Chain Phosphatase; D010748:Phosphopeptides / Q000302:isolation & purification; D010749:Phosphoprotein Phosphatases / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation; D014357:Trypsin; D000096985:Calponins
D017301:Ca(2+) Mg(2+)-ATPase; D002135:Calcium-Binding Proteins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D043263:Myosin-Light-Chain Phosphatase; D010748:Phosphopeptides; D010749:Phosphoprotein Phosphatases; D014357:Trypsin; D000096985:Calponins