Phosphorylation and dephosphorylation of Mg2+-independent Ca2+-ATPase from goat spermatozoa
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Dephosphorylation
Dephosphorylation
Response regulator
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The phosphorylation and dephosphorylation reactions of the proteins of isolated rat liver nuclei were examined in the presence of ATP. It was shown that the plateau value of the phosphorus incorporation at high concentrations of ATP is the result of an equilibrium of phosphorylation and dephosphorylation. The data of 32P-labelling experiments and those of chemical determination of net change of phosphorus content were compared. The activity of an efficient protein phosphatase in rat liver nuclei is demonstrated. It was shown that the pool of protein-phosphorus in the nuclei is heterogeneous as regards its turnover rate. A protein-phosphorus fraction of high turnover dominates the picture of phosphorylation and dephosphorylation reactions when studied with [gamma-32P] ATP in vitro.
Dephosphorylation
Phosphorus-32
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To study rhodopsin (Rho) phosphorylation and dephosphorylation in Royal College of Surgeons (RCS) rat retina, specific antibodies toward major Rho phosphorylation sites in vivo, 334Ser or 338Ser, were prepared by immunization of authentic phosphorylated peptides in rabbit. Enzyme-linked immunosorbent assay identified that the raised antibodies exclusively recognized either the phosphorylated 334Ser or 338Ser site. In immunofluorescence labeling, both antibodies recognized photoreceptor outer segments in light-adapted retinas from Sprague-Dawley (SD), Brown-Norway (BN) and RCS rat. During dark adaptation, immunoreactivities toward phosphorylated 338Ser and 334Ser sites were diminished within several hours (0.2-2 h) in SD and BN rat retinas. However, those toward phosphorylated 338Ser and 334Ser sites were diminished within 4 to 7 days in RCS rat retinas. In vitro studies demonstrated decreased levels of both Rho phosphorylation and dephosphorylation reactions in RCS retinas. However, the dephosphorylation reaction was much more greatly affected than the phosphorylation reaction. Extremely prolonged survival of phosphorylated forms of Rho may contribute to persistent misregulation of phototransduction processes in retinal degeneration in RCS rat.
Dephosphorylation
Visual phototransduction
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Dephosphorylation
Hyperphosphorylation
Tau protein
Autophagy-related protein 13
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The deinhibitor protein, responsible for the decreased sensitivity of the ATP, Mg‐dependent protein phosphatase to inhibitor‐1 and the modulator protein, is inactivated by cyclic AMP‐dependent protein kinase and reactivated by dephosphorylation. The specificity of this reaction was tested with the ATP, Mg‐dependent phosphatase in its activated or spontaneously active form, four different forms of polycation‐stimulated phosphatases (PCS H , PCS M , PCS L and PCS C ) and calcineurin. Only the high ‐ M r , polycation‐stimulated protein phosphatase (PCS H ), but not its catalytic subunit (PCS C ), shows a high degree of specificity for the deinhibitor protein. Deinhibitor phosphatase activity of PCS H is affected neither by polycations nor by Mn ions.
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Protein phosphatase 1
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Enzymatic phosphorylation and dephosphorylation reactions were used to modify a genetically engineered variant of spider dragline silk. The ∼25 kDa protein was phosphorylated with cyclic AMP-dependent kinase and dephosphorylated with calf intestinal alkaline phosphatase. Phosphorylation inhibited β-sheet assembly of the protein and enhanced solubility to about 5 mg/mL in water, compared to about 20% of this level upon enzymatic dephosphorylation. The cyclability of the phosphorylation−dephosphorylation system was confirmed by MALDI with a model peptide. Kinetic studies conducted with [γ-32P]ATP illustrate that the phosphorylation reaction proceeds over 6 h. Secondary structure of the phosphorylated and dephosphorylated proteins was determined by CD and FTIR. The results illustrate that an enzymatic phosphorylation event can be used to control the solution structure of a protein like silk, which has a tendency to prematurely precipitate due to the formation of β-sheets.
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Dephosphorylation
Imidazole
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Inhibitor-2, purified by an improved procedure, was used to identify protein phosphatases capable of catalysing its dephosphorylation. The results showed that, under our experimental conditions, protein phosphatases-1, 2A and 2B were the only significant protein phosphatases in rabbit skeletal muscle extracts acting on this substrate. Protein phosphatases-1 and 2A accounted for all the inhibitor-2 phosphatase activity in the absence of Ca2+ (resting muscle), and the potential importance of these enzymes in vivo is discussed. Protein phosphatase-2B, a Ca2+-calmodulin-dependent enzyme, could account for up to 30% of the inhibitor-2 phosphatase activity in contracting muscle. The Km of protein phosphatase-1 for inhibitor-2 (40 nM) was 100-fold lower than the Km for phosphorylase a (4.8 microM). This finding, coupled with the failure of inhibitor-2 to inhibit its own dephosphorylation, suggests that inhibitor-2 is dephosphorylated at one of the two sites on protein phosphatase-1 involved in preventing the dephosphorylation of other substrates. The dephosphorylation of inhibitor-2 by protein phosphatase-1 was also unaffected by inhibitor-1, suggesting that the phosphorylation state of inhibitor-2 is unlikely to be controlled by cyclic AMP in vivo.
Dephosphorylation
Protein phosphatase 1
DUSP6
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Dephosphorylation
Phosphorylation cascade
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It has been reported that heparin coexists with the hyperphosphorylated tau in the brain of the patients of Alzheimer’s disease [7] . The effect of heparin on phosphorylation by NCLK and dephosphorylation by PP2B of tau protein has been studied. Heparin was observed to improve the phosphorylation of tau, to increase the formation of tau dimers and decrease tau monomers. The first order rate constants of dimer increasing and monomer decreasing were 2 88×10 -3 s -1 and 1 74×10 -3 s -1 respectively. PP2B catalyzed dephosphorylation of the phosphorylated tau by NCLK and heparin improved such dephosphorylation. It suggests that heparin may regulate the phosphorylation and dephosphorylation of tau.
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Tau protein
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