Pumps, protein

ITowever, membrane proteins can also be distributed in nonrandom ways across the surface of a membrane. This can occur for several reasons. Some proteins must interact intimately with certain other proteins, forming multisubunit complexes that perform specific functions in the membrane. A few integral membrane proteins are known to self-associate in the membrane, forming large multimeric clusters. Bacteriorhodopsin, a light-driven proton pump protein, forms such clusters, known as purple patches, in the membranes of Halobacterium halobium (Eigure 9.9). The bacteriorhodopsin protein in these purple patches forms highly ordered, two-dimensional crystals. 

FIGURE 10.8 A schematic diagram of the Na, K -ATPase in mammalian plasma membrane. ATP hydrolysis occurs on the cytoplasmic side of the membrane, Na ions are transported out of the cell, and ions are transported in. The transport stoichiometry is 3 Na out and 2 in per ATP hydrolyzed. The specific inhibitor ouabain (Figure 7.12) and other cardiac glycosides inhibit Na, K -ATPase by binding on the extracellular surface of the pump protein. 

Currently, five different molecular classes of mdr efflux pumps are known [5], While pumps of the the ATP-binding cassette (ABC) transporter superfamily are driven by ATP hydrolysis, the other four superfamilies called resistance-nodulation-division (RND), major facilitator superfamily (MFS), multidrug and toxic compound extrusion (MATE), and small multidrag resistance transporter (SMR) are driven by the proton-motive force across the cytoplasmic membrane. Usually a single pump protein is located within the cytoplasmic membrane. However, the RND-type pumps which are restricted to Gram-negative bacteria consist of two additional components, a periplasmic membrane fusion protein (MFP) which connects the efflux pump to an outer... 

The procedure for purification of Na,K-ATPase in membrane-bound form from the outer renal medulla of mammalian kidney offers the opportunity of exploring the structure of the Na,K-pump proteins in their native membrane environment. The protein remains embedded in the membrane bilayer throughout the purification procedure thus maintaining the asymmetric orientation of the protein in the baso-lateral membrane of the kidney cell in the purified preparation. This preparation has been particularly useful in studies of ultrastructure, protein conformation and for... 

A characteristic structural feature of the renal Na,K-pump protein is a cytoplasmic protrusion with approximate dimensions 45 x 65 A in the plane of the membrane and a length of 50-60 A in the plane perpendicular to the membrane. The bulk of the protrusion is formed by the large central domain (residues 340-780 in a subunit)... 

Jorgensen, P.L. (1982). Mechanism of the Na/K pump. Protein structure and conformations of the pure Na/K ATPase. Biochim. Biophys. Acta 694, 27-68. 

Figure 8 Localization of solute (propranolol) within the lipid bilayer. This solute-membrane interaction has been shown to influence the conformation and activity of a calcium-pump protein (X) embedded in the bilayer. (From Ref. 78.)... 

The environmental inorganic and organic chemicals bind to the insides and outsides of selective and regulated membrane pumps (proteins) and act as on/off switches of the pumps. 

H+-ATPase an ion-pumping protein responsible for energy-dependent movement of H+ across biological membranes. 

Fig. s.n On-line continuous-flow monitoring of biochemical interaction with (a) fluorescence and (b) MS SIM (m/z 390) detection. Fluorescein-biotin (96 nM), streptavidin (32 nM), 20-pL loop injections of 1000 nM biotin (n = 3). MS instrument Q-ToF2 (Waters) equipped with a Waters Z-spray electrospray (ESI) source. Point 1 Carrier pump, protein and reporter ligand pumps... 

Palytoxin targets the sodium-potassium pump protein by binding to the molecule in such a way that the molecule is locked in a position where it allows passive transport of both the sodium and potassium ions, thereby destroying the ion gradient that is essential for most cells. 

There are at least two conformations of the ion pump proteins.552,5523 In one conformation the protein binds three sodium ions tightly, while in the other conformation it binds two potassium ions. The ATP operates the "motor" that carries out the conformational changes. In Fig. 8-25 the ion pump, in conformation A, is shown embedded in a membrane. 

Much of current interest in vanadium stems from the discovery that vanadate (HV042 at pH 7) is a powerful inhibitor of ATPases such as the sodium pump protein (Na+ + K+)ATPase (Chapter 8), of phosphatases,623 and of kinases.624 This can be readily understood from comparison of the structure of phosphate and vanadate ions. 

These results strengthen the "indirect-link" concept, and further suggest that the acyclic modifiers, 1, specifically inhibit the activation of proton pumps associated with the ATPase and the respiratory activities as a result of an implantation process at the corresponding protogenic pump proteins. It is likely that this inhibition is achieved by hydrogen bonding of carboxyl, hydroxyl, keto and amino groups in the acyclic modifier, 1, with certain membrane proteins. 

Figure 3.1 Proteins come in different shapes and sizes (a) the enzyme glutamine synthetase, (b) the protein fibrin, and (c) the calcium pump protein.

In the absence of a-type ions from their cytoplasmic uptake sites, the pump protein displays an alternative catalytic specificity the aspartyl residue can no longer react with ATP, but it readily phosphorylates from inorganic phosphate... 

Jdrgensen, P.L. Andersen, J.P. (1988). Structural basis for EpEj conformational transitions in Na,K-pump and Ca-pump proteins. J. Membr. Biol. 103,95-120. 

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