Phosphorylation by cAMP-dependent protein kinase

In order to determine what phosphorylation event(s) might lead to regulation of the channels by PKA, studies of the phosphorylation of the channel subunits have 

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Phosphorylation by cAMP-dependent protein kinases inactivates the reductase. This inactivation can be reversed by two specific phosphatases (Figure 25.33). 

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. 

A significant functional and structural feature of the plasma membrane Ca pumps is the presence of the calmodulin-binding subdomains A and B near the C-terminus (Fig. 3), that imparts calmodulin sensitivity on the Ca transport and ATP hydrolysis [3]. Adjacent to the calmodulin-binding region are two acidic segments (AC) and the P(S) region containing a serine residue that is susceptible to phosphorylation by cAMP-dependent protein kinase [34]. A unique feature of the plasma membrane Ca pump is its activation by acidic phospholipids that are presumed to... 

FIGURE 21-6 Schematic illustration of the overall structure and regulatory sites of eleven different phosphodiesterase subtypes. The catalytic domain of the phosphodiesterases are relatively conserved, and the preferred substrate(s) for each type is shown. The regulatory domains are more variable and contain the sites for binding of Ca2+/calmodulin (CaM) and cGMP, as well as GAF and PAS domains. The regulatory domains also contain sites of phosphorylation by cAMP-dependent protein kinase (PKA). 

Phosphorylation of the P-adrenergic receptor by PARK, like its phosphorylation by the cAMP-dependent enzyme, represents an example of negative feedback. However, unlike phosphorylation by cAMP-dependent protein kinase, phosphorylation by PARK represents an example of homologous desensitization only the P-adrenergic receptor would be affected in this process and, moreover, only those receptor molecules occupied by ligand would be affected. 

Additional information <1> (<1> two other cAMP-independent kinases found, that phosphorylate but do not effect acetyl-CoA carboxylase kinase activity [6] <1> phosphorylation by cAMP-dependent protein kinase has the same effect on acetyl-CoA carboxylase activity then phosphorylation with acetyl-CoA carboxylase kinase-2 [6,7] <1> cAMP-dependent protein kinase identified, that phosphorylates and inactivates acetyl-CoA carboxylase in vitro, but appears not to be involved in regulation in vivo [8]) [6-8]... 

Glucagon inhibits fatty acid synthesis in liver [123] and the inhibition is correlated with decreased activity of acetyl-CoA carboxylase [124,125], The inhibition of the enzyme is due to its phosphorylation by cAMP-dependent protein kinase [125,126] which causes a decrease in the Vm.M and an increase in the Ku for citrate [126],... 

Incubation of hepatocytes with glucagon also increases the phosphorylation of another lipogenic enzyme ATP-citrate lyase [127,128], The purified enzyme is also phosphorylated by cAMP-dependent protein kinase in vitro [128,129] resulting in a 2-fold increase in the Km for ATP [130], However, it is unclear what role this plays in the inhibition of lipogenesis. 

Studies have shown that NF-kB signaling is also regulated by phosphorylation of Rel proteins themselves. RelA (p65), the most dominant NF-kB protein, is phosphorylated by cAMP-dependent protein kinase at Ser276, which enhances its transcription function (Zhong et al., 1997). RelA phosphorylation can occur before IkB degradation, which creates a moiety that is primed and sitting on ready. In some cases, the phosphorylation of RelA can occur after the dissociation from IkB... 

The sarcoplasmic reticulum (SR) calcium pump together with phosphorylation of specific proteins, has an important role in myocardial contraction and relaxation. Phospholamban, a 20-24 kDa proteolipid, is phosphorylated by cAMP-dependent protein kinase as well as calmodulin-dependent protein kinase. Phosphorylation of this protein results in stimulation of Ca +-ATPase and Ca + transport by the SR (Scheme 4.1.1). ... 

The phospholipase Cf enzymes are subject to a variety of regulatory influences. Phosphorylation by cAMP-dependent protein kinases ( protein kinase A) and by protein kinase C link the /f-isoforms to heterologous and homologous receptor pathways. 

Additional information <6, 8, 22, 35, 37> (<8> phosphorylation by cAMP-dependent protein kinase, L- and R-type isozyme, [43] <8> no phosphorylation [50] <35> increasing buffer concentrations inhibit, least inhibitory imi-dazole-HCl [23] <22> interacting effects of various activators and inhibitors... 

The data described above suggest that the ADP-ribosylated arginine may be sequenced near serine residue 38 which is phosphorylated by cAMP-dependent protein kinase (Fig. 3). In the experiment of protein kinase-catalyzed phosphorylation of synthetic peptide, Zetterqvist et al. [9] and Kemp et al. [10] proposed that two arginine residues are necessary at the N-terminal side of phosphate-accepting serine residue. Therefore, we speculated that the ADP-ribosylation may influence the cAMP-dependent protein kinase activity. Actually, we found that when whole histones from calf thymus were... 

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