Cyclic adenosine monophosphate-dependent protein kinases

Dl-iike receptors activate the Gs transduction pathway, stimulating the production of adenylyl cyclase, which increases the formation of cyclic adenosine monophosphate (cAMP) and ultimately increases the activity of cAMP-dependent protein kinase (PKA). PKA activates DARPP-32 (dopamine and cyclic adenosine 3, 5 -monophosphate-regulated phosphoprotein, 32 kDa) via phosphorylation, permitting phospho-DARPP-32 to then inhibit protein phosphatase-1 (PP-1). The downstream effect of decreased PP-1 activity is an increase in the phosphorylation states of assorted downstream effector proteins regulating neurotransmitter... 

TTie second messenger, for example cyclic adenosine monophosphate (cAMP), then activates cAMP-dependent protein kinase which modulates the function of a broad range of membrane receptors, intracellular enzymes, ion channels and transcription factors. 

Knighton, D.R., Zheng, I, Ten Eyck, L.F., Ashford, V.A., Xuong, N., Taylor, S.S. and Sowadski, . M. Crystal structure of the catalytic subunit of cyclic adenosine monophosphate-dependent protein kinase (1991) Science 253, 407-413... 

Adenylate cyclase is considered as a second messenger that catalyzes the formation of cAMP (cyclic adenosine monophosphate) from ATP this results in alterations in intracellular cAMP levels that change the activity of certain enzymes—that is, enzymes that ultimately mediate many of the changes caused by the neurotransmitter. For example, there are protein kinases in the brain whose activity is dependent upon these cyclic nucleotides the presence or absence of cAMP alters the rate at which these kinases phosphorylate other proteins (using ATP as substrate). The phosphorylated products of these protein kinases are enzymes whose activity to effect certain reactions is thereby altered. One example of a reaction that is altered is the transport of cations (e.g., Na+, K+) by the enzyme adenosine triphosphatase (ATPase). 

D.R. Knighton, J.H. Zheng, L. TenEyck, N.H. Xuong, S.S. Taylor, and J.M. Sowadski. 1991. Structure of a peptide inhibitor bound to the catalytic subunit of cyclic adenosine monophosphate-dependent protein kinase Science 253 414-420. (PubMed)... 

Cyclic adenosine monophosphate-dependent protein kinase is useful for phosphorylation of a.a. residues in mild conditions. The modification makes the soybean proteins soluble in media rich in calcium and improves their emulsifying properties (Seguro and Motoki, 1990). 

In keeping with their proposed cytoskeletal nature, IFPs initially were thought to serve a purely structural role in muscle cells. It was hypothesized that the function of these proteins was to keep other cytoplasmic proteins in proper relationship to one another, as well as to anchor the cytoplasmic contractile apparatus to the cell membrane. Flowever, subsequent developments in cell biology cast considerable doubt on this premise." The intermediate filaments are now known to serve a nucleic acid-binding function moreover, they are susceptible to processing by calcium-activated proteases and are substrates for cyclic adenosine monophosphate-dependent protein kinases. Thus, it has been proposed that all IFPs serve as modulators between extracellular influences governing calcium flux into the cell (and subsequent protease activation) and nuclear function at a transcriptional... 

Phosphofructokinase 2 (PFK-2) is negatively regulated by phosphorylation in the liver (the enzyme that catalyzes the phosphorylation is the cyclic adenosine monophosphate [cAMP]-dependent protein kinase). However, in skeletal muscle, PFK-2 is not regulated by phosphorylation. This is because the skeletal muscle isozyme of PFK-2 lacks the regulatory serine residue, which is phosphorylated in the liver. However, the cardiac isozyme of PFK-2 is phosphorylated and activated by a kinase cascade initiated by insulin. This allows the heart to activate glycolysis and to use blood glucose when blood glucose levels are elevated. 

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