Characterization of calmodulin-mediated phosphorylation of cardiac muscle sarcoplasmic reticulum
| Autor: | Charles F. Louis, Mark Maffitt |
|---|---|
| Rok vydání: | 1982 |
| Předmět: |
inorganic chemicals
Calmodulin ATPase Biophysics Biochemistry Ryanodine receptor 2 Dephosphorylation Adenosine Triphosphate Dogs Cations Cyclic AMP medicine Animals Phosphorylation Protein kinase A Molecular Biology biology Chemistry Myocardium Endoplasmic reticulum Calcium-Binding Proteins Cardiac muscle Hydrogen-Ion Concentration musculoskeletal system Trifluoperazine Sarcoplasmic Reticulum medicine.anatomical_structure biology.protein Calcium Protein Kinases |
| Zdroj: | Archives of Biochemistry and Biophysics. 218:109-118 |
| ISSN: | 0003-9861 |
| DOI: | 10.1016/0003-9861(82)90326-5 |
| Popis: | Sarcoplasmic reticulum, isolated from canine cardiac muscle, was phosphorylated in the presence of exogenous cAMP-dependent protein kinase or calmodulin. This phosphorylation has been shown previously to activate sarcoplasmic reticulum calcium uptake (LePeuch et al. (1979) Biochemistry 18 , 5150–5157). Calmodulin appeared to activate an endogenous protein kinase present in sarcoplasmic reticulum membranes. The incorporation of phosphate increased with time. However, once all the ATP was consumed, the level of phosphorylated protein started to decrease due to the action of an endogenous protein phosphatase. Dephosphorylation occurred even when the level of phosphorylated sarcoplasmic reticulum remained constant at high ATP concentrations. The phosphorylation of sarcoplasmic reticulum in the presence of calmodulin, increased as the pH was increased from pH 5.5 to 8.5. This phosphorylation was only inhibited by KCl concentrations greater than 100 m m . The apparent K m of cAMP-dependent protein kinase for ATP was 5.2 ± 0.2 × 10 −5 m , and of the calmodulin-dependent protein kinase for ATP was 3.67 ± 0.29 × 10 −5 m . Phosphorylation was maximally activated by 5–10 m m MgCl 2 ; higher MgCl 2 concentrations inhibited this phosphorylation. Thus the calmodulin-dependent phosphorylation of cardiac sarcoplasmic reticulum could be maximally activated at sarcoplasmic concentrations of K + , Mg 2+ , and ATP. The calmodulindependent phosphorylation was half-maximally activated at Ca 2+ concentrations that were significantly greater than those required to promote the formation of the sarcoplasmic reticulum Ca-activated ATPase phosphoprotein intermediate. Thus at sarcoplasmic Ca 2+ concentrations that might be expected during systole, the sarcoplasmic reticulum calcium pump would be fully activated before any significant calmodul-independent sarcoplasmic reticulum phosphorylation occurred. However, under certain pathological conditions when the sarcoplasmic Ca 2+ becomes elevated (e.g., in ischemia) the kinase could be activated so that the sarcoplasmic reticulum would be phosphorylated and calcium uptake augmented. Thus, the calmodulin-dependent protein kinase may only function when the heart needs to rescue itself from a possibly fatal calcium overload. |
| Databáze: | OpenAIRE |
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