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Properties of phosphorylated myofibrils from gizzard smooth muscle
Abstract:
Phosphorylation of chicken gizzard myosin light chain in myofibril and its effect on myofibrillar ATPase activity were investigated in the contracted state of myofibrils. When myofibrils were incubated for two hours at 30 degreeds C with ATP, magnesium and calcium, the myosin light chain was phosphorylated by endogenous light-chain kinase. Standing overnight, the phosphorylated light chain was dephosphorylated by endogenous light-chain phosphatase. Control myofibril had much higher ATPase activity than phosphorylated and phosphorylated-dephosphorylated myofibrils. It was very interesting that the phosphorylated and phosphorylated-dephosphorylated myofibrils were quite similar in ATPase activity. However, phosphorylated myofibril differed from phosphorylated-dephosphorylated myofibril in Ca2+ dependency of Mg2+-ATPase activity. The phosphorylated-dephosphorylated myofibril was not affected by the presence or absence of Ca2+. In contrast, phosphorylated myofibril apparently showed a negative Ca2+-sensitivity. On the other hand, the results indicating that the superprecipitation gel formed by phosphorylated-dephosphorylated myosin could not be dissolved in 0.6 M NaCl, suggest that the phosphorylation-dephosphorylation process of the actomyosin system in gizzard myofibril results in stronger actin-myosin interaction.
Insights
Chicken gizzard myosin light chain phosphorylation affects myofibrillar ATPase activity. This process influences actin-myosin interactions, impacting muscle contraction dynamics.
Area of Science:
- Muscle Physiology
- Biochemistry
Background:
- Myosin light chain (MLC) phosphorylation is a key regulatory mechanism in muscle contraction.
- Understanding MLC phosphorylation in smooth muscle, like chicken gizzard, is crucial for elucidating contractile functions.
Purpose of the Study:
- To investigate the effects of MLC phosphorylation and dephosphorylation on chicken gizzard myofibrillar ATPase activity.
- To examine the Ca2+ dependency of Mg2+-ATPase activity in phosphorylated and dephosphorylated myofibrils.
- To assess the impact of the phosphorylation-dephosphorylation cycle on actin-myosin interactions.
Main Methods:
- Incubation of chicken gizzard myofibrils with ATP, magnesium, and calcium to induce phosphorylation by endogenous light-chain kinase.
- Allowing myofibrils to stand overnight for dephosphorylation by endogenous light-chain phosphatase.
- Measurement of myofibrillar ATPase activity and Ca2+ dependency.
- Assessment of superprecipitation gel formation and solubility in 0.6 M NaCl.
Main Results:
- Phosphorylated and phosphorylated-dephosphorylated myofibrils exhibited lower ATPase activity compared to control myofibrils.
- Phosphorylated-dephosphorylated myofibrils showed no Ca2+ dependency in Mg2+-ATPase activity.
- Phosphorylated myofibrils displayed negative Ca2+-sensitivity.
- Superprecipitation gels formed by phosphorylated-dephosphorylated myosin were insoluble in 0.6 M NaCl, indicating stronger actin-myosin interactions.
Conclusions:
- MLC phosphorylation and dephosphorylation significantly modulate chicken gizzard myofibrillar ATPase activity.
- The phosphorylation-dephosphorylation cycle alters the Ca2+ sensitivity of Mg2+-ATPase activity.
- This process enhances actin-myosin interaction strength in the gizzard actomyosin system.