Myosin light chain kinase phosphorylation: regulation of the Ca2+ sensitivity of contractile elements.
Purified myosin light chain kinase from smooth muscle is phosphorylated by cyclic AMP-dependent protein kinase, protein kinase C and the multifunctional calmodulin-dependent protein kinase II. Since phosphorylation in a specific site (site A) by any one of these kinases desensitizes myosin light chain kinase to activation by Ca2+/calmodulin, kinase phosphorylation could play an important role in regulating smooth muscle contractility. This possibility was investigated in 32P-labelled bovine tracheal smooth muscle. Treatment of tissues with carbachol, KCl, isoproterenol, or phorbol 12,13-dibutyrate increased the extent of kinase phosphorylation. Six primary phosphopeptides (A-F) of myosin light chain kinase were identified. Site A was phosphorylated to an appreciable extent only with carbachol or KCl, agents which contract tracheal smooth muscle. The extent of site A phosphorylation correlated to increases in the concentration of Ca2+/calmodulin required for activation. These results show that cyclic AMP-dependent protein kinase and protein kinase C do not affect smooth muscle contractility by phosphorylating site A in myosin light chain kinase. It is proposed that phosphorylation of myosin light chain kinase in site A, perhaps by calmodulin-dependent protein kinase II, may play a role in reported desensitization of contractile elements in smooth muscle to activation by Ca2+.
Stull
J T
JT
University of Texas Southwestern Medical Center, Department of Physiology, Dallas 75235.
Tansey
M G
MG
Word
R A
RA
Kubota
Y
Y
Kamm
K E
KE
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000502:physiology*; D006801:Humans; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000201:enzymology / Q000502:physiology*; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism*; D010766:Phosphorylation
D009219:Myosin-Light-Chain Kinase; D002118:Calcium