Protein kinase A


Protein kinase A (PKA) is a family of enzymes whose activity is dependent on cellular levels of cyclic AMP (cAMP). 

PKA is also known as cAMP-dependent protein kinase.

Also known as adenosine 3′,5′-monophosphate (cyclic AMP)-dependent protein kinase, abbreviated to PKA.

PKA’s functions in the cell include: regulation of glycogen, sugar, and lipid metabolism.

Phosphokinase A is an enzyme that regulates various cellular processes by adding phosphate groups to target molecules. 

It functions by phosphorylating specific proteins, leading to changes in their activity, localization, or interactions within the cell. 

This phosphorylation process can activate or deactivate target proteins, thereby influencing various cellular functions such as metabolism, gene expression, and cell growth.

It is made up of four subunits.

When inactive, it exists as a tetramer which consists of two regulatory subunits and two catalytic subunits. 

Cells have at least two types of PKAs:

Type I is mainly in the cytosol, whereas type II is bound via its regulatory subunits and special anchoring proteins

to the plasma membrane, nuclear membrane, mitochondrial outer membrane, and microtubules. 

In both types of PKAs: once the catalytic subunits are freed and active, they can migrate into the nucleus (where they can phosphorylate transcription regulatory proteins), while the regulatory subunits remain in the cytoplasm.

PKA is also commonly known as cAMP-dependent protein kinase, because it has traditionally been thought to be activated through release of the catalytic subunits when levels of the second messenger called cyclic adenosine monophosphate, or cAMP, rise in response to a variety of signals. 

Hormones, such as glucagon and epinephrine, begin an intracellular signalling cascade that triggers protein kinase A activation by first binding to a G protein–coupled receptor (GPCR) on the target cell. 

The liberated catalytic subunits catalyze the transfer of ATP terminal phosphates to protein substrates at serine, or threonine residues. 

PKA regulation and cAMP regulation are involved in many different pathways and may be divided into direct protein phosphorylation and protein synthesis.

Downregulation of protein kinase A occurs by a feedback mechanism and uses a number of cAMP hydrolyzing phosphodiesterase (PDE) enzymes, which belong to the substrates activated by PKA. 

Phosphodiesterase quickly converts cAMP to AMP, thus reducing the amount of cAMP that can activate protein kinase A. 

Epinephrine and glucagon affect the activity of protein kinase A by changing the levels of cAMP in a cell via the G-protein mechanism, using adenylate cyclase. 

Protein kinase A acts to phosphorylate many enzymes important in metabolism. 

Protein kinase A (PKA) is an enzyme that plays a critical role in regulating various cellular processes in response to external signals such as hormones and neurotransmitters. 

It is involved in the phosphorylation of target proteins, which can lead to changes in their activity, localization, and interactions with other molecules. 

PKA is a key player in many signaling pathways and is essential for numerous physiological functions in the body.

Protein kinase A phosphorylates acetyl-CoA carboxylase and pyruvate dehydrogenase, and has an inhibitory effect on these enzymes, thus inhibiting lipogenesis and promoting net gluconeogenesis. 

Insulin decreases the level of phosphorylation of these enzymes, which instead promotes lipogenesis.

PKA helps transfer/translate the dopamine signal into cells in the nucleus accumbens.

The nucleus accumbens mediates reward, motivation, and task salience. 

The majority of reward perceptions involve neuronal activation in the nucleus accumbens, including sex, recreational drugs, and food. 

Protein Kinase A signal transduction pathway helps in modulation of ethanol’s consumption and  sedative effects. 

PKA gets activated and phosphorylates numerous targets, namely: L-type calcium channels, phospholamban, troponin I, myosin binding protein C, and potassium channels, 

This increasing contraction force as well as enabling the muscles to relax faster.

PKA is considered important in formation of a memory. 

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