Affinity membrane

B. Evaluation of Cell Membrane Affinity In Vivo Interaction with Rat intestinal Cells... 

C. Evaluation of Membrane Affinity In Vitro Interaction with Liposomal Lipid Bilayer... 

Loidl-Stahlhofen, A., Eckert, A., Hartmann, T Schottner, M. Solid-supported lipid membranes as a tool for determination of membrane affinity high-throughput screening of a physicochemical parameter. J. Pharm. Sci. 2001, 90, 599-606. 

Binding of Prenylated and Polybasic Peptides to Membranes Affinities and Intervesicle Exchange, F. Gho-mashchi, X. Zhang, L. Liu, M. H. Gelb, Biochemistry 1995, 34,11910-11918. 

Acylation is used by the cell for diverse purposes, the most common being membrane association. The membrane affinity of soluble proteins is increased via acylation, which affects the localization and function of proteins. This is found for singly and dually lipidated proteins. The localization of doubly lipidated proteins is determined by dynamic palmitoylation and depalmitoylation. Palmitoylation is therefore a tool for regulating protein trafficking in the cell. The most prominent examples are the small Ras GTPases. 

Martin JD, Ito Y, Flomann VV, Flaygood MG, Butler A (2006) Stmcture and Membrane Affinity of New Amphiphilic Siderophores Produced by Ochrobactrum sp. SP18. J Biol Inorg Chem 11 633... 

Xu G, Martinez JS, Groves JT, Butler A (2002) Membrane Affinity of the Amphiphilic Marinobactin Siderophores. J Am Chem Soc 124 13408... 

Table 1.1 shows the preferential binding of chlorphentermine to phosphatidylcholine-containing membranes, the phospholipid with overall acidic charge. These systems predict the actual affinity of the compound for the membrane, rather than its ability to cross the membrane. Membrane affinity, and hence tissue affinity, is particularly important in the persistence of drugs within the body, a topic which wiU be covered in Section 4.2. 

N-Myristoylation is achieved by the covalent attachment of the 14-carbon saturated myristic acid (C14 0) to the N-terminal glycine residue of various proteins with formation of an irreversible amide bond (Table l). 10 This process is cotranslational and is catalyzed by a monomeric enzyme called jV-myri s toy 11ransferase. 24 Several proteins of diverse families, including tyrosine kinases of the Src family, the alanine-rich C kinase substrate (MARKS), the HIV Nef phosphoprotein, and the a-subunit of heterotrimeric G protein, carry a myr-istoylated N-terminal glycine residue which in some cases is in close proximity to a site that can be S-acylated with a fatty acid. Functional studies of these proteins have shown an important structural role for the myristoyl chain not only in terms of enhanced membrane affinity of the proteins, but also of stabilization of their three-dimensional structure in the cytosolic form. Once exposed, the myristoyl chain promotes membrane association of the protein. 5 The myristoyl moiety however, is not sufficiently hydrophobic to anchor the protein to the membrane permanently, 25,26 and in vivo this interaction is further modulated by a variety of switches that operate through covalent or noncovalent modifications of the protein. 4,5,27 In MARKS, for example, multiple phosphorylation of a positively charged domain moves the protein back to the cytosolic compartment due to the mutated electrostatic properties of the protein, a so-called myristoyl-electrostatic switch. 28 ... 

Hoffman et al. [46, 47] found that an LCST polymer remains strongly bound to a substrate, especially to cellulose acetate (CA), at a temperature above its LCST, whereas most of the adsorbed polymer molecules are easily rinsed off below the LCST. For instance, they synthesized a room-temperature-precipit-able terpolymer (LCST = 7-13 °C), consisting of IPAAm, A-butylacrylamide (BAAm) and N-acryloxy succinimide (NASI), which was conjugated to a murine monoclonal antibody. They developed the membrane-affinity concentration immunoassay [48]. 

Additionally, it was noticed that flavones were slightly more hydrophobic than flavanones possessing the same number of hydroxyl groups [103]. Flavonols turned out to be the least hydrophobic from all the compounds studied. The degree of DPH fluorescence quenching in PC liposomes by flavonoids was used as a measure of the relative membrane affinity of these... 

Serpa G, Augusto EFP, Tamashiro WMSC, Ribeiro MB, Miranda EA, Bueno SMA (2005), Evaluation of immobilized metal membrane affinity chromatography for purification of IgGl monoclonal antibody, J. Chromatogr. B 816 259-268. 

PURPOSE AND RATIONALE Lipophilicity expressed as logPow correlates with membrane affinity and other biological properties as summarised in Kern s (2001) review on physicochemical profiling. However, the interfacial (anisotropic) character of bilayer membranes and the ionisable phospholipid head groups of biological membranes influence the partition properties of drugs. These... 

Using liposomes for membrane affinity studies has the great advantage that liposomes are a nearly one-to-one model of biological bilayer membranes. Liposomes can be generated from a variability of lipids and mixtures of lipids in order to study the influence of the membrane constituents on the partition behaviour of drag candidates. 

However, the throughput of liposome partition assays is limited as preparation and validation of liposomes are very time consuming. That seems to be the main reason why liposome partitioning is not widely used in the pharmaceutical industry to date. On the other hand, the results obtained using liposome partitioning show that liposomes are unique tools to study the bilayer membrane affinity (MA) of drugs and their correlation to intestinal membrane absorption. 

The use of solid-supported lipid membranes (SSLM) to measure membrane affinity was recently reported by Loidl-Stahlhofen (2001a, 2001b). To produce solid-supported lipid membranes a single phospholipid bilayer membrane is non covalently... 

A good correlation between logMASsLM andlogMA estimated from equilibrium dialyses using liposomes in solution was reported. The TRANSIL approach is a unique use of liposome like real bilayer membranes as high throughput method for the estimation of membrane affinity. 

Tammela P, Laitinen L, Galkin A et al. (2004) Permeability characteristics and membrane affinity of flavonoids and alkyl gallates in Caco-2 cells and in phospholipid vesicles. Arch Biochem Biophys 425 193-199... 

Methylation has also been found to enhance the membrane affinity of a number of different Icmt substrates. Of particular interest has been the effect of methylation on the biology of the proto-oncoprotein Ras. In an early study, K-Ras produced by in vitro translation was found to be farne-sylated, but further modification including proteolysis and methylation required incubation with intracellular membranes. Unmethylated K-Ras produced by in vitro translation in the presence of pancreatic microsomes and an inhibitor of methylation, methylthioadenosine (MTA), was found to associate less efficiently with PlOO membrane fractions from COS cells than the fully modified protein [55]. In other in vitro studies, farnesylated peptides corresponding to the C-terminus of Ras had 20-fold higher affinity for liposomes when methylated [56]. 

---