User:Rmcconne/ATPase

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Mechanism of Action
The coupling of ATP hydrolysis and transport is a chemical reaction in which a fixed number of solute molecules are transported for each ATP molecule hydrolyzed; for the Na+/K+ exchanger, this is three Na+ ions out of the cell and two K+ ions inside per ATP molecule hydrolyzed.

Transmembrane ATPases make use of ATP's chemical potential energy by performing mechanical work: they transport solutes in the opposite direction of their thermodynamically preferred direction of movement—that is, from the side of the membrane with low concentration to the side with high concentration. This is referred to as active transport.

For instance, inhibiting vesicular H+-ATPases would result in a rise in the pH within vesicles and a drop in the pH of the cytoplasm.

ATPase ( also called F1F0 ATP Synthase) is a charge-transferring complex that catalyzes ATP to perform ATP synthesis by moving ions through the membrane. All of these enzymes share a common basic structure. Each rotary ATPase is composed of two major components: F0/A0/V0 and F1/A1/V1. They are connected by 1-3 stalks to maintain stability, control rotation, and prevent them from rotating in the other direction. One stalk is utilized to transmit torque. The number of peripheral stalks is dependent on the type of ATPase: F-ATPases have one, A-ATPases have two, and V-ATPases have three. The F1 catalytic domain is located on the N-side of the membrane and is involved in the synthesis and degradation of ATP and is involved in oxidative phosphorylation. The F0 transmembrane domain is involved in the movement of ions across the membrane.

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The bacterial F0F1-ATPase consists of the soluble F1 domain and the transmembrane F0 domain, which is composed of several subunits with varying stoichiometry. There are two subunits, γ, and ε, that form the central stalk and they are linked to F0. F0 contains a c-subunit oligomer in the shape of a ring (c-ring). The α subunit is close to the subunit b2 and makes up the stalk that connects the transmembrane subunits to the α3β3 and δ subunits. F-ATP synthases are identical in appearance and function except for the mitochondrial F0F1-ATP synthase, which contains 7-9 additional subunits.

The electrochemical potential is what causes the c-ring to rotate in a clockwise direction for ATP synthesis. This causes the central stalk and the catalytic domain to change shape. Rotating the c-ring causes three ATP molecules to be made, which then causes H+ to move from the P-side of the membrane to the N-side of the membrane. The counterclockwise rotation of the c-ring is driven by ATP hydrolysis and ions move from the N-side to the P-side, which helps to build up electrochemical potential.

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Structure
The Walker motifs are a telltale protein sequence motif for nucleotide binding and hydrolysis. Beyond this broad function, the Walker motifs can be found in almost all natural ATPases, with the notable exception of tyrosine kinases. The Walker motifs commonly form a Beta sheet-turn-Alpha helix that is self-organized as a Nest (protein structural motif). This is thought to be because modern ATPases evolved from small NTP-binding peptides that had to be self-organized.

Protein design has been able to replicate the ATPase function (weakly) without using natural ATPase sequences or structures. Importantly, while all natural ATPases have some beta-sheet structure, the designed "Alternative ATPase" lacks beta sheet structure, demonstrating that this life-essential function is possible with sequences and structures not found in nature.

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Heading
ATPases (EC 3.6.1.3, Adenosine 5'-TriPhosphatase, adenylpyrophosphatase, ATP monophosphatase, triphosphatase, SV40 T-antigen, ATP hydrolase, complex V (mitochondrial electron transport), (Ca2+ + Mg2+)-ATPase, HCO3−-ATPase, adenosine triphosphatase) are a class of enzymes that catalyze the decomposition of ATP into ADP and a free phosphate ion or the inverse reaction. This dephosphorylation reaction releases energy, which the enzyme (in most cases) harnesses to drive other chemical reactions that would not otherwise occur. This process is widely used in all known forms of life.

Some such enzymes are integral membrane proteins (anchored within biological membranes), and move solutes across the membrane, typically against their concentration gradient. These are called transmembrane ATPases.