Calmodulin acts by -

Ans. is 'b' i.e., Phosphorylation of myosine by protein kinaseo In smooth muscle there is no troponin.o Therefore calcium initiates contraction through a mechanism different from that employed by skeletal muscle.o Smooth muscle contains a calcium binding protein called calmodulin.o Increase in cytoplasmic (sarcoplasmic) calcium leads to its binding to calmodulin.o The calcium-calmodulin complex activates myosin kinase, also called myosin light chain kinase(MLCK).o MLCK is a phosphorylase whichphosphorylates a light chain belonging to myosin chain, often called cross-bridge phosphorylation.o The phosphorylated myosin head interact with actin, i.e., cross-bridging of myosin with actin.o The cross-bridging leads to contraction.Binding of acetylcholine to muscarinic receptors|Increased influx of Ca2+ into the cell|Activation of calmodulin-dependent myosin light chain kinase|Phosphorylation of myosin|Increased myosin ATPase activity and binding of myosin to actin|Contraction|Dephosphorylation of myosin by myosin light chain phosphatase|Relaxation, or sustained contraction due to latch bridge and other mechanisms