PUMPS SITES FOR ATPase
- A Pump or ion transporter is a transmembrane protein that moves ions across a plasma membrane against their concentration gradient through active transport.
- They utilized energy to transport ions
- The primary transporters are enzymes that convert energy from various sources including ATP sunlight and other redox -reaction to potential energy which is stored in an electrochemical gradient.
- This potential energy is then used by secondary transporters including ion carrier and ion channel;
- A active transport pump may be uni-porter or anti-porter
- ATP dependent ion pumps are grouped into classes based on transport mechanisms as well as genetic and structural homology.
- All ATP powered pumps are transmembrane proteins with one or more binding sites.
- ATP located on the cytosolic face of the membrane .
- These proteins are commonly called ATPase
- The ATP hydrolyzed into ADP and Pi and the energy is used to move ions or other molecule uphill against an electrochemical gradient
Types of Pumps
- There are four types/ Classes (P,V,F, and ABC) of ATP powered pumps.
- In these three classes (P,F, and V) transports ions only.
- where as ABC superfamily transport small molecules.
P- Class Pumps (ATP powered Pump)
- These are found in plasma membrane of plant fungi and bacteria
- All P class ion pump posses two identical catalytic α sub-unit that contain an ATP binding site and an β sub-unit that usually have regulatory function.
- During the transport process α sub-unit is phosphorylated (hence the name “P” Class) and the transported ions through the phosphorylated sub-unit.
- They included
(i) Na+K+ATPase
- It is present in plasma membrane of most animal cell
- These are antiport ion pumps
- They catalyze ATP dependent Transport of Na+ out of a cell in exchange for K+ entering the cell.
(ii) H+- K+ ATPase
- These are involved in acid secretion in the stomach
- These are antiport pump
- They catalyzed ATP dependent transport of H+ out of the gastric parietal ell (to ward the stomach lumen) in exchange for K+ entering the cell
(iii) Ca 2+ ATPase
- It is present in the endoplasmic reticulum (E.R.) and plasma membrane of many cells.
- This catalyzes ATP dependent transport of Ca2+ away from the cytosol into the E.R. lumen or out of the cell.
- These pumps are antiporters transporting protons in the opposite direction.
- Ca2+ ATPase pump function to keep cytosolic Ca2+ conc low. allowing Ca2+ to serve as a signal.
V -Classes pump
- All V-class ATPase transport only H+ ions
- These proton pumps present in the membranes of lysosomes, endosomes and plant vacuoles functions to acidify the lumen of these organelles.
- These V. Class proton pumps contain two domain a-cytosolic hydrophilic domain (V1) and a transmembrane domain (V0) with multiple subunits in each domain.
- Binding and hydrolysis of ATP by the β subunits in (V1) provide the energy for pumping of H+ ions through the proton- conducting channel formed by the “C” and “a” subunit in V0.
- V class proton pumps are not phosphorylated and dephosphorylated during proton transport.
- V Class pumps generally function to maintain the low pH of plant vacuoles and lysosome and other acidic vesicles in animal cells by pumping protons from the cytosolic to the exoplasmic face of the membrane against a proton electrochemical gradient.
F Class Pump
- The structures of F-class and V-class ion pumps are similar to one another but unrelated to and more complicated than P-class pumps.
- F- class pumps contain several different transmembrane and cytosolic subunits.
- All known F pumps transport only protons, in a process that does not involve a phosphoprotein intermediate.
- F-class pumps are found in bacterial plasma membranes and in mitochondria and chloroplasts. In contrast to V pumps, they generally function to power the synthesis of ATP from ADP and Pi by movement of protons from the exoplasmic to the cytosolic face of the membrane down the proton electrochemical gradient.
- Because of their importance in ATP synthesis in chloroplasts and mitochondria, F-class proton
pumps, commonly called ATP synthases.
ABC (ATP binding Cassette) transporter
- These catalyze trans-membrane movement of organic compounds including amphipathic lipids and drugs.
- It is organized by four core domains.
- These domain consist of two transmembrane (T) domain and two cytosolic (A) domain.
- The two T domain alternate b/w an inward and outward facing orientation.
- This alternation is powered by the hydrolysis of ATP.
- ATP bind to A sub-unit and it is then hydrolyzed to power the alternation.
- These four domain can be present in four separate polypeptides.
E.g.
- CUT 1 (Carbohydrate uptake Transporter 1)
- PAAT (polar amino acid uptake transporter )
- PepT, PhoT
