Cyclic AMP dependent kinase

Noradrenaline acts on three types of receptor. The ai receptors mediate the main excitatory effects of noradrenaline upon wake-active neurons in the dorsal raphe, basal forebrain, and elsewhere (Vandermaelen Aghajanian, 1983 Nicoll, 1988 Fort et al., 1995 Brown et al., 2002). The a2 receptors mediate inhibitory effects of noradrenaline, e.g. on noradrenaline neurons themselves and on cholinergic brainstem neurons (Williams et al., 1985 Williams Reiner, 1993). The (3-receptors modulate neurons in a more subtle fashion, increasing excitability via blockade of afterhyperpolarizations in hippocampal and cortical neurons (Haas Konnerth, 1983). Activation of (3-receptors also promotes synaptic plasticity via activation of the cyclic-AMP-dependent kinase (PKA) and cyclic AMP response element binding protein (CREB) signal transduction pathway (Stanton Sarvey, 1987 Cirelli et al., 1996). 

Phosphorylation of HI during mitosis is catalyzed by the cyclin B-Cdc2 kinase, a tightly regulated enzyme [25,26]. In Tetrahymena mitotically dividing nuclei, cyclic-AMP dependent kinase (PKA) or PKA-like kinase phosphorylates HI [27,28]. Protein phosphatase 1 dephosphorylates the phosphorylated HI [29]. 

Figure 11-2 Roles of phosphofructose kinase and fructose 1,6-bisphosphatase in the control of the breakdown and storage (—+) of glycogen in muscle. The uptake of glucose from blood and its release from tissues is also illustrated. The allosteric effector fructose 2,6-bisphosphate (Fru-2,6-P2) regulates both phosphofructokinase and fructose 2,6-bisphosphatase. These enzymes are also regulated by AMP if it accumulates. The activity of phosphofructokinase-2 (which synthesizes Fru-2,6-P2) is controlled by a cyclic AMP-dependent kinase and by dephosphorylation by a phosphatase.

Cyclic AMP can affect the synthesis of catecholamines by two separate modes of action on the rate-limiting catecholamine-synthesizing enzyme tyrosine hydroxylase. Cyclic AMP-dependent kinase can phosphorylate tyrosine hydroxylase, which in turn results in activation of the enzyme. Furthermore, in peripheral tissues such as the adrenal medulla, cAMP can result in the de novo synthesis of tyrosine hydroxylase by causing a derepression of gene expression due to the translocation of the catalytic subunit of the kinase to the chromaffin cell nucleus. 

Taylor, S. S., Radzio-Andzelm, E. Cyclic AMP-dependent protein kinase. In Protein Kinases, Woodgett, J. R., editor, IRL Press, Oxford, 1994. 

Steinberg, R. A. A kinase-negative mutant of s49 mouse lymphoma cells is defective in posttranslational maturation of catalytic subunitof cyclic amp-dependent protein kinase. Mol. Cell Biol. 11 (1991) 705-712. 

A number of kinase structures have been determined in various catalytic states. For example, structures of the cyclin-dependent kinase, CDK2, in its inactive state and in a partially active state after cyclin binding have been discussed in Chapter 6. The most thoroughly studied kinase is the cyclic AMP-dependent protein kinase the structure of both the inactive and the active... 

Cyclic AMP-dependent protein kinase is shown complexed with a pseudosubstrate peptide (red). This complex also includes ATP (yellow) and two Mn ions (violet) bound at the active site. 

FIGURE 15.7 Cyclic AMP-dependent protein kinase (also known as PKA) is a 150- to l70-kD R9C9 tetramer in mammalian cells. The two R (regulatory) subunits bind cAMP ( = 3 X 10 M) cAMP binding releases the R subunits from the C (catalytic) subunits. C subunits are enzymatically active as monomers. 

Earner, J., 1990. Insulin and the stimulation of glycogen synthesis The road from glycogen structure to glycogen synthase to cyclic AMP-dependent protein kinase to insulin mediators. Advances in Enzymology 63 173-231. 

Group II assays consist of those monitoring cellular second messengers. Thus, activation of receptors to cause Gs-protein activation of adenylate cyclase will lead to elevation of cytosolic or extracellularly secreted cyclic AMP. This second messenger phosphorylates numerous cyclic AMP-dependent protein kinases, which go on to phosphorylate metabolic enzymes and transport and regulatory proteins (see Chapter 2). Cyclic AMP can be detected either radiometrically or with fluorescent probe technology. 

AKAPs are cyclic AMP-dependent protein kinase (PKA)-anchoring proteins, a family of about 30 proteins anchoring PKA at subcellular sites in close vicinity to a certain substrate. 

Cyclic nucleotides (cAMP and cGMP) are formed enzymatically from the corresponding triphosphates. As ubiquitous second messengers, they mediate many cellular functions which are initiated by first (extracellular) messengers. Their prime targets in eucaryotic cells are protein kinases ( cyclic AMP-dependent protein kinase, cyclic GMP-dependent protein kinase), ion channels and ensymes. 

Protein kinase A (PKA) is a cyclic AMP-dependent protein kinase, a member of a family of protein kinases that are activated by binding of cAMP to their two regulatory subunits, which results in the release of two active catalytic subunits. Targets of PKA include L-type calcium channels (the relevant subunit and site of phosphorylation is still uncertain), phospholam-ban (the regulator of the sarcoplasmic calcium ATPase, SERCA) and key enzymes of glucose and lipid metabolism. 

Sharma, R. and Wang, J. H. Differential regulation of bovine brain calmodulin-dependent cyclic nucleotide phosphodiesterase isozzymesdby cyclic AMP-dependent protein kinase and calmodulin-dependent protein phosphatase. Proc. Natl Acad. Sci. U.S.A. 82 2603-2607,1986. 

Couve, A., Thomas, P, Calver, A. R., et al. (2002) Cyclic AMP-dependent protein kinase phosphorylation facilitates GABAb receptor-effector coupling. Nat. Neurosci. 25,25. 

Timchalk C, Charles AK. 1986. Differential effects of carcinogens on hepatic cytosolic cyclic AMP-dependent protein kinase activity. J Am Coll Toxicol 5(4) 267-273. 

Roth, N. S., Campbell, P. T., Caron, M. G., Lefkowitz, R. J., and Lohse, M. J. (1991) Comparative rates of desensitization of beta-adrenergic receptors by the beta-adrenergic receptor kinase and the cyclic AMP-dependent protein kinase. Proc. Natl. Acad. Sci. U. S. A. 88, 6201-6204. 

Cyclic AMP-dependent protein kinase (protein kinase-A). 

Adrenaline increases the rate of gluconeogenesis it binds to the a-receptor on the surface of the liver cell, which results in an increase in cytosolic concentration of Ca " ions (Chapter 12). This increases the activity of the Ca " -catmodulin-dependent protein kinase which phosphory-lates and causes similar changes in the activities of the enzymes PFK-2 and pyruvate kinase to those resulting from activation of cyclic-AMP-dependent protein kinase. Hence Ca " ions increase the rate of gluconeogenesis. 

Figure 7.15 Inhibition of acetyl-CoA carboxylase by cyclic AMP dependent protein kinase and AMP dependent protein kinase the dual effect of glucagon. Phosphorylation of acetyl-CoA carboxylase by either or both enzymes inactivates the enzyme which leads to a decrease in concentration of malonyl-CoA, and hence an increase in activity of carnitine palmitoyltransferase-I and hence an increase in fatty acid oxidation. Insulin decreases the cyclic AMP concentration maintaining an active carboxylase and a high level of malonyl-CoA to inhibit fatty acid oxidation.

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). 

Chambers TC, Pohl J, Glass DB, Kuo JF (1994) Phosphorylation by protein kinase C and cyclic AMP-dependent protein kinase of synthetic peptides derived firom the linker region of human P-glycoprotein. Biochem J 299 309-315... 

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