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Phosphorylation of paramyosin
S Watabe1, T Tsuchiya, D J Hartshorne
1Laboratory of Marine Biochemistry, Faculty of Agriculture, University of Tokyo, Japan.
Abstract:
1. Myofibrils isolated from Mercenaria mercenaria were phosphorylated by endogenous kinase. Over a range of ionic strengths only paramyosin was phosphorylated. 2. Thiophosphorylation of paramyosin caused an inhibition of steady-state actin-activated ATPase activity of the myofibrils. 3. It is proposed that the endogenous kinase is the catalytic subunit of the cAMP-dependent protein kinase. 4. The sequence around the phosphorylation site was determined. 5. The phosphorylation site probably is close to the C-terminus of the paramyosin molecule.
Insights
The study found that phosphorylating paramyosin in Mercenaria mercenaria myofibrils inhibits ATPase activity. This suggests a role for cAMP-dependent protein kinase in muscle contraction regulation.
Area of Science:
- Muscle physiology
- Biochemistry
- Marine biology
Background:
- Myofibrils are the basic contractile units of muscle cells.
- Paramyosin is a myosin-associated protein found in invertebrate muscles.
- Protein phosphorylation plays a crucial role in regulating muscle function.
Purpose of the Study:
- To investigate the endogenous phosphorylation of myofibrils from Mercenaria mercenaria.
- To determine the effect of paramyosin phosphorylation on myofibril ATPase activity.
- To identify the kinase responsible for paramyosin phosphorylation.
Main Methods:
- Isolation of myofibrils from Mercenaria mercenaria.
- In vitro phosphorylation assays using endogenous kinase.
- Measurement of actin-activated ATPase activity.
- Amino acid sequencing around the phosphorylation site.
Main Results:
- Only paramyosin was phosphorylated by the endogenous kinase across various ionic strengths.
- Thiophosphorylation of paramyosin inhibited steady-state actin-activated ATPase activity.
- The endogenous kinase is proposed to be the catalytic subunit of cAMP-dependent protein kinase.
- The phosphorylation site was localized near the C-terminus of paramyosin.
Conclusions:
- Endogenous phosphorylation of paramyosin in Mercenaria mercenaria myofibrils modulates muscle activity.
- The findings suggest a regulatory mechanism involving cAMP-dependent protein kinase in invertebrate muscle contraction.
- Paramyosin phosphorylation near the C-terminus may influence interactions critical for ATPase activity.