Alec Titan
Adenosine triphosphate (ATP) is a critical molecule for muscle contractions and energy transfer in biological processes. ATP hydrolysis is the process by which energy stored in high-energy phosphoanhydride bonds in ATP is released through the splitting of these bonds, resulting in the production of adenosine diphosphate (ADP) and an inorganic phosphate (Pi). This process powers muscle contractions by providing the energy required for the movement of muscle proteins, actin, and myosin. The hydrolysis of ATP by the enzyme ATPase, which is present at the binding site on myosin, is essential for the contraction cycle, allowing actin and myosin to interact and generate force. The power stroke, a key step in muscle contraction, occurs when ATP is hydrolyzed, releasing energy and causing the actin filament to slide past the myosin filament, resulting in muscle shortening and contraction. This review will focus on the specific muscle proteins that hydrolyze ATP and their roles in muscle contraction, energy production, and overall physiological functions.
| Characteristics | Values |
|---|---|
| Muscle proteins that hydrolyze ATP | Actin and myosin |
| The enzyme that hydrolyses ATP | ATPase |
| The energy released during ATP hydrolysis | Changes the angle of the myosin head into a "cocked" position |
| The energy source for the movement of muscle shortening | Energy is provided by ATP |
| The muscle protein that binds to actin | Myosin |
| The muscle protein that has a binding site for ATP | Myosin |
| The muscle protein that releases actin | Myosin |
| The muscle protein that binds to calcium ions | Troponin |
| The muscle protein that blocks myosin binding sites on actin molecules | Tropomyosin |
| The muscle protein that stabilizes the SRX state | Myosin-binding protein C (MyBP-C) |
| The role of ATP in muscle contraction | Provides energy for the power stroke |
| The products of ATP hydrolysis | ADP and inorganic phosphate (Pi) |
| The role of ADP and Pi | Form cross-bridges with actin and release energy during the power stroke |
| The role of ATP in signal transduction | Serves as a substrate for kinases, transferring phosphate groups |
| The role of ATP in the nervous system | Acts as a neurotransmitter |
| The role of ATP in muscle tissue | Discovered in muscle tissue by Karl Lohmann, Jendrassik, Cyrus Fiske, and Yellapragada Subba Rao |
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What You'll Learn
ATP hydrolysis and muscle contraction
Muscle contraction is a complex process involving the interaction of various proteins and enzymes. Adenosine triphosphate (ATP) is a critical molecule in this process, providing the energy required for muscle contraction. ATP hydrolysis releases the energy stored in the high-energy phosphoanhydride bonds of ATP, converting it into adenosine diphosphate (ADP) and an inorganic phosphate (Pi). This process is facilitated by the enzyme ATPase, which catalyses the decomposition of ATP.
ATP hydrolysis plays a key role in the cross-bridge cycle of muscle contraction. In resting muscles, actin and myosin are separated, and myosin is in a low-energy state. When a muscle contracts, calcium ions bind to the protein complex troponin, causing a conformational change that exposes the actin-binding sites. The high-energy myosin head then binds to actin, forming a cross-bridge. This binding is facilitated by ATP, which prepares myosin for binding by moving it to a high-energy "cocked" position.
Following the formation of the cross-bridge, Pi is released, and the myosin head undergoes a conformational change, moving towards the M-line in a step known as the power stroke. This movement produces force, pulling the actin filament towards the M-line, resulting in sarcomere shortening and muscle contraction. At this stage, ATP is hydrolysed into ADP and Pi, with the energy from ATP hydrolysis powering the power stroke. The power stroke concludes with the release of ADP, although the cross-bridge remains intact, keeping actin and myosin bound together.
For further muscle contraction to occur, ATP binds to myosin once more, breaking the cross-bridge and releasing the myosin head from the actin-binding site. This allows the cross-bridge cycle to begin anew, with myosin returning to its original position in the recovery stroke. The energy for this process is derived from ATP hydrolysis, which powers the repeated cycle of muscle contraction and relaxation.
Overall, ATP hydrolysis is essential for muscle contraction, providing the energy that fuels the cross-bridge cycle. The hydrolysis of ATP by the enzyme ATPase releases energy, enabling the power stroke and facilitating the repeated binding and releasing of actin and myosin, resulting in muscle contraction and relaxation.
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Myosin and ATP
Myosin is a motor protein that plays a crucial role in muscle contraction by interacting with actin, another protein present in muscles. This interaction between myosin and actin requires energy, which is provided by adenosine triphosphate (ATP).
ATP is a high-energy molecule that stores and releases energy, which is utilised by the body for various processes, including muscle contraction. During muscle contraction, myosin binds to actin at specific binding sites on the actin protein. Myosin also has a binding site for ATP. When ATP binds to myosin, it undergoes enzymatic hydrolysis, catalysed by the enzyme ATPase, converting ATP into adenosine diphosphate (ADP) and releasing an inorganic phosphate molecule (Pi) and energy. This energy is utilised to release actin from myosin, allowing them to detach from each other.
The hydrolysis of ATP by myosin results in a change in the conformation of the myosin head, moving it into a "cocked" position. In this position, the myosin head is primed for further movement, possessing potential energy, with ADP and Pi still attached. The myosin head remains in this high-energy configuration until the actin binding sites become available again.
Once the actin binding sites are uncovered, the high-energy myosin head forms a cross-bridge with actin, initiating the power stroke. During the power stroke, the myosin head moves towards the M-line, pulling the actin filament along with it. This movement results in the shortening of the sarcomere, leading to muscle contraction. As the myosin head moves through the power stroke, it expends its stored energy, transitioning from a high-energy to a low-energy state.
At the end of the power stroke, the myosin head releases ADP, but the cross-bridge with actin remains intact. ATP can then bind to myosin once again, allowing the cross-bridge cycle to restart and facilitating further muscle contraction. This cyclical process involving the interaction of myosin, actin, and ATP enables repeated muscle contractions, contributing to overall muscle function.
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ATP and actin
Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton and thin filaments in muscle fibrils. They are found in essentially all eukaryotic cells and are essential for important cellular functions such as cell division and cell mobility. Actin is a monomeric subunit of two types of filaments in cells: microfilaments, one of the three major components of the cytoskeleton, and thin filaments, part of the contractile apparatus in muscle cells.
Actin is an ATPase, an enzyme that can hydrolyze ATP. The hydrolysis of ATP by actin provides the structural cues for filament turnover in vivo. Actin filaments support cellular signalling, intracellular trafficking, and cytokinesis.
The binding of ATP or ADP is required to stabilize each actin monomer; without one of these molecules bound, actin quickly becomes denatured. The tertiary structure of actin is formed by two domains, the large and the small, which are separated by a cleft centred around the location of the bond with ATP-ADP+Pi. The cleft is also referred to as the "ATPase fold", as it is a structure conserved among ATP and GTP-binding proteins that bind to a magnesium ion and a molecule of ATP.
Actin-myosin pairs can participate in the trafficking of various membrane vesicles and organelles within the cell. Myosin moves along an actin filament, pulling its cargo along with it. These nonconventional myosins use ATP hydrolysis to transport cargo, such as vesicles and organelles, in a directed fashion much faster than diffusion.
The motion of muscle shortening occurs as myosin heads bind to actin and pull it inwards, requiring energy provided by ATP. The energy released during ATP hydrolysis changes the angle of the myosin head into a "cocked" position, allowing for further movement.
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ATP's role in energy supply
Adenosine triphosphate (ATP) is a nucleotide that consists of three main structures: a nitrogenous base (adenine), a sugar (ribose), and a chain of three phosphate groups bound to ribose. The phosphate tail of ATP is the actual power source tapped by the cell.
ATP is a crucial energy-carrying molecule found in the cells of all living things. It captures chemical energy obtained from the breakdown of food molecules and releases it to fuel other cellular processes. ATP is not a storage molecule for chemical energy; that is the job of carbohydrates, such as glycogen, and fats. Instead, ATP is an energy shuttle, delivering energy to places within the cell where energy-consuming activities are taking place.
ATP is stable in aqueous solutions between pH 6.8 and 7.4, but at more extreme pH levels, it rapidly hydrolyses to adenosine diphosphate (ADP) and inorganic phosphate. ATP hydrolysis is the catabolic reaction process by which chemical energy stored in the high-energy phosphoanhydride bonds in ATP is released after splitting these bonds, producing mechanical energy. The energy released during ATP hydrolysis is used to power essential processes in living organisms and cells, including muscle contraction, nerve impulse propagation, substrate phosphorylation, chemical synthesis, intracellular signalling, DNA and RNA synthesis, Purinergic signalling, synaptic signalling, and active transport.
ATP is consumed for energy in these processes, creating a high demand for ATP. As a result, human body cells depend on the hydrolysis of 100 to 150 moles of ATP per day to ensure proper functioning. The energy derived from food or sunlight is converted into ATP, which powers cellular processes by transferring a phosphate group to another molecule through phosphorylation. This transfer is carried out by special enzymes that couple the release of energy from ATP to cellular activities that require energy.
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ATP's discovery and uses
Adenosine triphosphate (ATP) is an energy-carrying molecule that fuels cellular functions. ATP was first discovered in the 1920s, specifically in 1929, from muscle tissue by Karl Lohmann and Jendrassik and, independently, by Cyrus Fiske and Yellapragada Subba Rao of Harvard Medical School. Both teams were competing against each other to find an assay for phosphorus.
ATP is the source of energy for use and storage at the cellular level. It is a nucleotide that consists of three main structures: the nitrogenous base adenine, the sugar ribose, and a chain of three phosphate groups bound to ribose. The phosphate tail of ATP is the actual power source tapped by the cell. Available energy is contained in the bonds between the phosphates and is released when they are broken through the process of hydrolysis. ATP is not a storage molecule for chemical energy; that is the job of carbohydrates, such as glycogen, and fats. Instead, ATP captures chemical energy obtained from the breakdown of food molecules and releases it to fuel other cellular processes.
ATP is consumed for energy in processes including ion transport, muscle contraction, nerve impulse propagation, substrate phosphorylation, and chemical synthesis. ATP is also a precursor to DNA and RNA and is used as a coenzyme. In addition to providing energy, the breakdown of ATP through hydrolysis serves a broad range of cell functions, including intracellular signalling and DNA/RNA synthesis. ATP is released from vesicular stores and regulated by IP3 and other common exocytotic regulatory mechanisms.
ATP has several clinical uses, including in cardiology, surgery, pain management, and anesthesia. For example, ATP administered through a vein (intravenously) can help control pain by acting on the A1 adenosine receptor. ATP is also being studied for its potential to decrease weight loss and improve muscle strength in people with advanced solid tumours.
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Frequently asked questions
ATP is short for adenosine triphosphate, a molecule that stores and releases energy.
ATP hydrolysis is the process of breaking down ATP into adenosine diphosphate (ADP) and an inorganic phosphate (Pi).
The muscle proteins actin and myosin hydrolyze ATP.
ATP binds to myosin, which then binds to actin. The enzymatic activity at the binding site on myosin hydrolyzes ATP into ADP and Pi, releasing energy.
ATP hydrolysis is necessary for muscle contraction. The energy released during hydrolysis powers the muscle contraction cycle, allowing actin and myosin to detach from each other and the muscle to relax.
