Аденозин монофосфаты: құрылымы, метаболизмі және қызметтері

Adenosine monophosphate (AMP), also known as 5' adenylic acid, is a nucleotide. AMP consists of a phosphate group, the sugar ribose, and the nucleobase adenine. It is an ester of phosphoric acid and the nucleoside adenosine. As a substituent it takes the form of the prefix adenylyl
AMP plays an important role in many cellular metabolic processes, being interconverted to adenosine triphosphate (ATP) and adenosine diphosphate (ADP), as well as allosterically activating enzymes such as myophosphorylase b. AMP is also a component in the synthesis of RNA. AMP is present in all known forms of life.

The eukaryotic cell enzyme 5' adenosine monophosphate activated protein kinase, or AMPK, utilizes AMP for homeostatic energy processes during times of high cellular energy expenditure, such as exercise. Since ATP cleavage, and corresponding phosphorylation reactions, are utilized in various processes throughout the body as a source of energy, ATP production is necessary to further create energy for those mammalian cells. AMPK, as a cellular energy sensor, is activated by decreasing levels of ATP, which is naturally accompanied by increasing levels of ADP and AMP. Though phosphorylation appears to be the main activator for AMPK, some studies suggest that AMP is an allosteric regulator as well as a direct agonist for AMPK. Furthermore, other studies suggest that the high ratio of AMP:ATP levels in cells, rather than just AMP, activate AMPK. AMP binds to the γ subunit of AMPK, leading to the activation of the kinase, and then eventually a cascade of other processes such as the activation of catabolic pathways and inhibition of anabolic pathways to regenerate ATP. Catabolic mechanisms, which generate ATP through the release of energy from breaking down molecules, are activated by the AMPK enzyme while anabolic mechanisms, which utilize energy from ATP to form products, are inhibited. Though the γ subunit can bind AMP/ADP/ATP, only the binding of AMP/ADP results in a conformational shift of the enzyme protein. This variance in AMP/ADP versus ATP binding leads to a shift in the dephosphorylation state for the enzyme. The dephosphorylation of AMPK through various protein phosphatases completely inactivates catalytic function. AMP/ADP protects AMPK from being inactivated by binding to the γ subunit and maintaining the dephosphorylation state.

AMP can also exist as a cyclic structure known as cyclic AMP (or cAMP). Within certain cells the enzyme adenylate cyclase makes cAMP from ATP, and typically this reaction is regulated by hormones such as adrenaline or glucagon. cAMP plays an important role in intracellular signaling. In skeletal muscle, cyclic AMP, triggered by adrenaline, starts a cascade (cAMP dependent pathway) for the conversion of myophosphorylase b into the phosphorylated form of myophoshorylase a for glycogenolysis.