What is ATP (Adenosine Triphosphate)?

What is ATP (Adenosine Triphosphate)?

ATP (adenosine triphosphate) is the primary energy currency molecule of all living cells, consisting of an adenosine nucleoside bound to three phosphate groups, which stores and transfers energy through phosphoryl group transfer reactions. 1

Molecular Structure and Basic Function

• ATP is composed of adenosine (the core molecule) linked to three phosphate groups, with energy stored in the high-energy phosphate bonds 1
• The molecule serves as the fundamental energy transfer unit, with approximately 90% of cellular ATP produced in mitochondria and less than 10% generated in the cytosol 2
• ATP functions through phosphoryl group transfer, producing adenosine diphosphate (ADP) and inorganic phosphate when energy is released 1, 3

Energy Metabolism and Production

• Mitochondria generate ATP through oxidative phosphorylation, where protons shuttle across the inner mitochondrial membrane to drive ATP synthase, converting ADP to ATP 1
• The inner mitochondrial membrane contains electron transport chain complexes that create the proton gradient necessary for ATP synthesis 1
• Energy metabolism occurs in three steps: (1) hydrogen release from water and nutrients, (2) proton gradient production during cellular respiration, and (3) ATP production by consuming this gradient 1
• In terms of efficiency, glucose yields approximately 120 kcal per liter of oxygen consumed, compared to 100 kcal from fat metabolism 1

Cellular Signaling and Regulatory Functions

• Beyond energy storage, ATP plays critical roles as a signaling molecule and neurotransmitter, particularly in pain transmission pathways in both the spinal cord and periphery 1
• Adenosine, derived from ATP breakdown, is recognized by specific purinergic receptors (A1, A2, P2X3) that regulate neuronal and non-neuronal cellular functions 1
• ATP serves as a phosphate donor for regulatory modifications of both small metabolites and large proteins 3
• The ATP-to-ADP ratio directly reflects cellular energy charge and phosphorylation potential, serving as a critical physiological control parameter 3

Clinical and Diagnostic Significance

• ATP concentration measurements are used clinically to evaluate cell viability, proliferation, death, and energy transmission 4
• In cardiovascular diagnostics, adenosine (formed from ATP dephosphorylation) is used pharmacologically to induce coronary hyperemia during physiological assessments, with a half-life in human blood of approximately 20 seconds 1
• ATP testing involves rapid bolus injection (20 mg) during ECG monitoring, though recent evidence shows limited predictive value for certain cardiac conditions 1
• Adenosine interacts with purinergic A2 receptors to increase cyclic adenosine monophosphate, causing vasorelaxation primarily in the microcirculation 1

Pathophysiological Implications

• Disturbances in ATP amount, cellular localization, or interaction with target elements can induce pathological changes leading to serious diseases including neurodegeneration, cardiovascular diseases, diabetes mellitus, obesity, and cancers 5
• In mitochondrial disorders, impaired respiratory chain function reduces ATP generation, particularly affecting high-energy organs like brain, muscle, liver, heart, and kidneys 1
• During ischemic stroke, decreased blood flow causes oxygen and glucose shortage, impairing ATP production and resulting in neurological dysfunction 1

Compartmental Distribution and Dynamics

• Real-time ATP dynamics differ between cytosolic and mitochondrial compartments, with glycolytic inhibition (2-deoxyglucose) substantially decreasing cytosolic ATP while complex V inhibition (oligomycin) markedly decreases mitochondrial ATP 2
• The ATP/ADP carrier (AAC) facilitates ATP trafficking between compartments, with AAC inhibition reducing both cytosolic and mitochondrial ATP under normoxic conditions 2
• During hypoxia with AAC inhibition, mitochondrial ATP is sustained while cytosolic ATP decreases, suggesting altered directional ATP transport 2