Proteins phosphorylase

It is instructive to note that the biochemistry of the reactions that initiate the visual cascade and the glycogenolytic cascade is similar. The cyclic AMP-dependent protein kinase complex comprises the regulatory and catalytic components (R and C) for which the regulatory signal is the concentration of cyclic AMP. This binds to the regulatory component of the kinase (the R subunit) which then dissociates from the R-C complex. The C is now catalyti-cally active and catalyses the initial reaction in a cascade sequence which leads to activation of the target protein (phosphorylase). 

First, the binding of one hormone molecule to one receptor catalytically activates several Gs molecules. Next, by activating a molecule of adenylyl cyclase, each active Gsa molecule stimulates the catalytic synthesis of many molecules of cAMP. The second messenger cAMP now activates PKA, each molecule of which catalyzes the phosphorylation of many molecules of the target protein—phosphorylase b kinase in Figure 12-16. This... 

Figure 3.9. SDS gel electrophoresis of MFGM proteins prepared by different washing procedures. S reference proteins phosphorylase B, bovine serum albumin, ovalbumin, carbonic anhydrase, trypsin inhibitor, a-lactal-bumin. (Courtesy of J. Basch and H. M. Farrell, Jr.)...

Fig.3 SDS-PAGE of SOD from Scots pine needles. Molecular weight calibration proteins phosphorylase b (94 kDa) albumin (67 kDa) ovalbumin (43 kDa) carbonic anhydrase 30 (kDa) trypsin inhibitor (20.1 kDa) -lactalbumin (14.4 kDa).

Fig. 1. Ultrogel AcA 54 chromatography of sARF I effect of dimyristoyl phosphatidylcholine (DMPC) on ADP-ribosylation of Gsa and choleragen A protein. Purified sARF I was chromatographed on a column (1.2 x 104 cm) of Ultrogel AcA 54. Fractions (1 ml) were collected and samples were (A) analyzed by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and assayed for ARF activity in a reaction mixture containing Gg (0.4 jig), choleragen (25 pg), and 100 pM GTP without (B) or with (C) 1 mM DMPC. (A) SDS-PAGE of 250 pi of fraction plus bovine serum albumin, 10 pg. Lanes 1-4, fractions 68, 72, 76 and 80 Lane 5, standard proteins, phosphorylase b, bovine serum albumin, ovalbumin, carbonic anhydrase, soybean trypsin inhibitor, a-lactalbumin. (B) and (C) Autoradiograms of ADP-ribosylated proteins. Lanes 1-4, fractions 68,72,76 and 80 Lane 5, column buffer.

Kinase An enzyme that attaches phosphate groups to proteins. Phosphorylase An enzyme that cleaves phosphate groups from proteins. 

FIGURE 6.28 Examples of protein domains with different numbers of layers of backbone strnctnre. (a) Cytochrome c with two layers of a-helix. (b) Domain 2 of phosphoglycerate kinase, composed of a /3-sheet layer between two layers of helix, three layers overall, (c) An nnnsnal five-layer strnctnre, domain 2 of glycogen phosphorylase, a /S-sheet layer sandwiched between four layers of a-helix. (d) The concentric layers of /S-sheet (inside) and a-helix (outside) in triose phosphate isomerase. Hydrophobic residnes are bnried between these concentric layers in the same manner as in the planar layers of the other proteins. The hydrophobic layers are shaded yellow. (Jane Richarelson)... 

Dephosphorylation of glycogen phosphorylase is carried out by phospho-protein phosphatase 1. The action of phosphoprotein phosphatase 1 inactivates glycogen phosphorylase. 

Stimulation of glycogen breakdown involves consumption of molecules of ATP at three different steps in the hormone-sensitive adenylyl cyclase cascade (Figure 15.19). Note that the cascade mechanism is a means of chemical amplification, because the binding of just a few molecules of epinephrine or glucagon results in the synthesis of many molecules of cyclic / MP, which, through the action of c/ MP-dependent protein kinase, can activate many more molecules of phosphorylase kinase and even more molecules of phosphorylase. For example, an extracellular level of 10 to 10 M epinephrine prompts the for-... 

In hver, one of the serine hydroxyl groups of active phosphorylase a is phosphorylated. It is inactivated by hydrolytic removal of the phosphate by protein phos-phatase-1 to form ph osphorylase h. Reactivation requires rephosphorylation catalyzed by phosphorylase kinase. 

Both phosphorylase a and phosphorylase kinase a are dephosphorylated and inactivated by protein phos-phatase-1. Protein phosphatase-1 is inhibited by a protein, inhibitor-1, which is active only after it has been phosphorylated by cAMP-dependent protein kinase. Thus, cAMP controls both the activation and inactivation of phosphorylase (Figure 18-6). Insulin reinforces this effect by inhibiting the activation of phosphorylase b. It does this indirectly by increasing uptake of glucose, leading to increased formation of glucose 6-phosphate, which is an inhibitor of phosphorylase kinase. 

Not only is phosphorylase activated by a rise in concentration of cAMP (via phosphorylase kinase), but glycogen synthase is at the same time converted to the inactive form both effects are mediated via cAMP-dependent protein kinase. Thus, inhibition of glycogenolysis enhances net glycogenesis, and inhibition of glycogenesis enhances net glycogenolysis. Furthermore,... 

Pantothenic acid is present in coenzyme A and acyl carrier protein, which act as carriers for acyl groups in metabolic reactions. Pyridoxine, as pyridoxal phosphate, is the coenzyme for several enzymes of amino acid metabolism, including the aminotransferases, and of glycogen phosphorylase. Biotin is the coenzyme for several carboxylase enzymes. 

NARDINI M, SCACCINI c, PACKER L and VIRGILI F (2000) In vivo inhibition of the activity of phosphorylase kinase, protein kinase C and protein kinase A by caffeic acid and a procyanidin rich pine bark (Pinus maritima) extract Biochimica Biophysica Acta 1474, 219-25. 

Protein phosphorylation Calmodulin kinase I ATI Elongation factor-2 kinase Phosphorylase kinase Myosin Light Chain kinase... 

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