P-type transporters

P-type transporters share the same general reaction mechanism 74 A major fraction of cerebral energy production is consumed by the Na+,K+ pump 75... 

ATP-dependent Ca2+ pumps and Na+,Ca2+ antiporters act in concert to maintain a low concentration of free cytosolic Ca2+ 79 The uniquely high resolution structural data available for the SERCAla Ca2+ pump illuminates the structure of all P-type transporters 81 P-type copper transporters are important for neural function 82... 

Transport ATPases transport cations—they are ion pumps. ATPases of the F type—e. g., mitochondrial ATP synthase (see p. 142)—use transport for ATP synthesis. Enzymes of the V type, using up ATP, pump protons into lyso-somes and other acidic cell compartments (see p. 234). P type transport ATPases are particularly numerous. These are ATP-driven cation transporters that undergo covalent phosphorylation during the transport cycle. 

The family of active transporters called P-type ATPases are ATP-driven cation transporters that are reversibly phosphorylated by ATP as part of the transport cycle phosphorylation forces a conformational change that is central to moving the cation across the membrane. All P-type transport ATPases have similarities in amino acid... 

Figure 1. Localization of the major types of ion-motive ATPases in the eukaryotic cell. Na+-K+, H+-K+, and Ca2+-ATPases of P-type transport the respective cations across the plasma membrane or into sarcoplasmic (SR) or endoplasmic (ER) reticulum. H+-ATPase of V-type acidifies different types of vacuoles and vesicles allowing their secondary uptake of amino acids and amines (AA+). H+-ATPase (working as ATP synthase) of F-type (FqF,) generates ATP in the mitochondria. Modified from Pedersen and Carafoli, 1987.

Figure 6.2 Schematic diagram of solar cells with extended junctions and an extremely thin absorber (a) Layer structure for a superstrate n-i-p cell in this configuration a highly structured ra-layer is deposited on a transparent conductive oxide (TCO) contact layer, then a conformal absorber layer is deposited, followed by a transparent p-type transport layer and finally a reflective metal contact (b) Band diagram for the n-i-p heterojunction. The valence-band edges Ey) and conduction band edges Ec) for the absorber and transport layers and the electron and hole quasi-Fermi levels are shown (c) Illustration of reduced transport paths in the absorber layer and extended optical paths due to scattering in the heterostructure (d) Extremely thin absorber cell with a comparably shallow structure and a metal back contact in place of a transparent transport layer.

At the end of this section we shall briefly discnss transport measurements on polycrystalline CuSCN and Cul films, which have been nsed as transparent p-type transport layers in some devices. 

This is of particular interest since for all pentacene-based thin film transistors using high work function electrodes (such as gold) only p-type transport has been found although pentacene is intrinsically an ambipolar semiconductor. Note, that previously n-type transport has only been observed in connection with low work function electrodes such as calcium [80] (see also Chapter 24 by Benson et al.). In accord with previous findings by Friend and coworkers [78] we propose that we can observe n-conduction in our model device because the presence of any OH-groups at the SAM/pentacene interface can be safely excluded by the use of ultra-clean electrodes. 

The Ca +-transport ATPases belong to the group of P-type transport ATPases, which are characterized by the transfer of the y-phosphate of ATP to the enzyme... 

Working principles of organic solar cells are well described in a recent review and some monographs. More or less all types of organic solar cells described above comprise two components in the photoactive layer. One component serves as electron donor, whereas the other works as electron acceptor. Absorption of photons by the active layer components results in the electron transfer from donor to acceptor. This process called photoinduced charge transfer is a fundamental principle of operation of all known organic photovoltaic devices as well as the natural photosynthetic systems. In many cases, donor material is capable of efficient p-type transport and therefore can be called as p-type organic semiconductor. At the same time, electron acceptor material is denoted as n-type semiconductor in many cases. 

F iGURE 3.7 The role of ATP in active transport — P-type transporters which have to bephosphorylated in order to permit transport across the cell membrane. 

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