Meta-Biol

• Pathways

The P-type ATPases (E1-E2 ATPases) are a large group of evolutionarily related ion pumps that are found in bacteria, archaea and eukaryotes. They are referred to as P-type ATPases because they catalyze auto-phosphorylation of a key conserved aspartate residue within the pump. They all appear to interconvert between at least two different conformations, E1 and E2. Most members of this transporter family pump a large variety of cations (Kuhlbrandt W, 2004).

Ion channels mediate the flow of ions across the plasma membrane of cells. They are integral membrane proteins, typically a multimer of proteins, which, when arranged in the membrane, create a pore for the flow of ions. There are different types of ion channels. P-type ATPases undergo conformational changes to translocate ions. Ligand-gated ion channels operate like a gate, opened or closed by a chemical signal. Voltage-gated ion channels are activated by changes in electrical potential difference at the membrane (Purves, 2001; Kuhlbrandt, 2004).

By definition cells have a critical separation between inner (cytoplasmic) and outer (extracellular) compartments. This separation provides for protection, gradient assembly, and environmental control but at the same time isolates the interior compartments of the cell from energy resources, oxygen, and raw materials. Cells have evolved a myriad of mechanisms to regulate, and enable transportation of small molecules ascross plasma membranes and between cellular organelle compartments within cells.