Proteins, membrane dissociation constant

KDHRF A homologous restriction factor binds to C8 65KDHRF A homologous restriction factor, also known as C8 binding protein interferes with cell membrane pore-formation by C5b-C8 complex Kcat Catalytic constant a measure of the catalytic potential of an enzyme Ka Equilibrium dissociation constant kD Kilodalton Kd Dissociation constant KD Kallidin... 

Transporters recognize and bind the molecules to be transported and help them to pass through the membrane as a result of a conformational change. These proteins (permeases) are thus comparable with enzymes—although with the difference that they catalyze vectorial transport rather than an enzymatic reaction. Like enzymes, they show a certain affinity for each molecule transported (expressed as the dissociation constant, in mol L ) and a maximum transport capacity (V). 

A measurement system that is able to quantitatively determine the interactions of receptor and G protein has the potential for more detailed testing of ternary complex models. The soluble receptor systems, ([l AR and FPR) described in Section II, allow for the direct and quantitative evaluation of receptor and G protein interactions (Simons et al, 2003, 2004). Soluble receptors allow access to both the extracellular ligandbinding site and the intracellular G protein-binding site of the receptor. As the site densities on the particles are typically lower than those that support rebinding (Goldstein et al, 1989), simple three-dimensional concentrations are appropriate for the components. Thus, by applying molar units for all the reaction components in the definitions listed in Fig. 2A, the units for the equilibrium dissociation constants are molar, not moles per square meter as for membrane-bound receptor interactions. These assemblies are also suitable for kinetic analysis of ternary complex disassembly. 

There are many ways in which hormone-receptor interactions may be studied, the classic method being the Scatchard technique, named in honor of George Scatchard. This technique is applicable to any protein-small molecule interaction, and it provides a means of determining the heterogeneity of binding sites, dissociation constants, and the number of binding sites per receptor unit. The last may be a protein molecule, a cell, a cell membrane fragment, or a unit volume of cytosol with a known protein content. 

After Fe + siderophores have docked at the binding pocket of the outer-membrane receptors of E. colt, translocation into the periplasmic space is mediated by the TonB complex. Once released into the periplasm, siderophores are rapidly bound by the specific periplasmic binding proteins FhuD (hydroxamate siderophores), FepB (enterobactin), and FecB (ferric dicitrate).FhuD, for example, exhibits a broad substrate specificity for a variety of hydroxamate siderophores including ferrichrome, coprogen, aerobactin, ferrioxamine B, shizokinen, rhodotorulic acid, and the antibiotic albomycin. The dissociation constants of FhuD with these siderophores range from 0.3 to 5.4 X-ray structures of FhuD... 

An amino acid binding protein (presumably involved in membrane transport) was isolated from E. coli. Equilibrium dialysis measurements at 25 and 3TC yielded Ks values of 8.8X10 and 3.0xiO M, respectively. (Xs is the dissociation constant of the protein-substrate complex.) Calculate (a) AG for the binding reaction at 25 and 37 C, (b) AH for the binding reaction, and (c) AS for the binding reaction at 25 C. (d) What does the sign and... 

A solution of the protein (0.5 mg/ml) was placed in one compartment of a dialysis chamber. An equal volume of buffer containing 4x 10" M L-leucine-C was placed in the other compartment. The compartments are separated by a semipermeable membrane through which the labeled amino acid can move freely. The protein, however, is restricted to one compartment. After equilibration, the compartment containing the protein had 2.3x10 total (bound 4-free) L-leucine-C. The compartment without protein contained 1,7 X 10 M Ldeucine-C. Calculate (a) the concentration of bound L-leudne-C [PS] or [S]i, (b) the concentration of free protein, [P]/, and (c) the dissociation constant for the protein-leucine complex assuming one bindir site per molecule of protein. 

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