(myosin-light-chain) phosphatase

The myosin light chain phosphatase ( MLCP also or myosin light chain phosphatase ) is an enzyme that is present in the cells of smooth muscles. You dephosphorylated regulatory light chain of myosin. This usually leads to a relaxation of the smooth muscles. MLCP is a dimer of the catalytic subunit PPP1CB ( EC 3.1.3.53 ) and the regulatory subunit (one of PPP1R12A/B/C ) for determining the substrate. Binding of PPP1CB other subunits leads to different substrate specificities.

MLCP has an antagonistic effect on the enzyme of the myosin light chain kinase.

The catalyzed reaction is:

Mechanism of action

Increase the relaxant signaling cascades with the second messenger cAMP or cGMP the activity of protein kinase A (PKA ) and protein kinase G (PKG ). This in turn leads to an increased activity of myosin light chain phosphatase. In effect it cleaves a phosphate from the light chain of myosin, which lowers the calcium sensitivity of myofilaments. It is now compels higher Ca2 - concentrations, to induce a contraction. In sum, thus increasing the relative proportion of relaxed muscle in smooth muscle. About what mechanism PKA and PKG increase the activity of MLCP is not yet precisely known. It is believed to interact with the Rho / Rho kinase pathway.

Regulation together with the myosin light chain kinase

Phosphorylation of the myosin is also regulated by the myosin light chain kinase MLCK. The two enzymes MLCK and MLCP with antagonistic action hold the muscle in a specific phosphorylation and tension. This is a high activity of the MLCK contraction and a high activity of MLCP relaxation of smooth muscle, for example, of vessels and bronchi. Therefore, the activities of MLCK and MLCP the diverse neurohumoral regulated by the autonomic nervous system, the paths should be antagonistic to activate the enzyme and inhibit the other. Examples:

  • α1 -adrenoceptor: ( Gq - coupled ) [ IP3 ] ↑, [ Ca2 ] ↑, [ Ca2 calmodulin complex ] ↑, ↑ MLCK activity
  • α1 -adrenoceptor: ( Gq - coupled ) [ DAG ] ↑, ↑ PKC activity, MLCP activity ↓
  • β2 - adrenergic receptor ( Gs - coupled ) [ cAMP ] ↑, ↑ PKA activity, MLCK activity ↓
  • β2 - adrenergic receptor ( Gs - coupled ) [ cAMP ] ↑, ↑ PKA activity, MLCP activity ↑
  • Guanylate cyclase ( soluble): ( by binding of NO ) [ cGMP ] ↑, ↑ PKG activity, MLCP activity ↑
Smooth muscle tissue Proteinkinase A Proteinkinase C
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