Membrane distribution

The membrane-associated small G proteins H-Ras and K-Ras have been studied with respect to their association with cytoplasmic leaflets. These two proteins have nearly identical structures and functions but different membrane anchors, membrane distributions and effector responses. Application of the FRAP method to fluorescent constructs of H-Ras and K-Ras revealed that only H-Ras in its guanosine 5 diphosphate (GDP)-bound form associates with cholesterol-dependent rafts [26]. 

A summary of the membrane distribution of Cu, Fe and Zn transporters in plants is presented in Figure 8.13. 

Figure 8.13 Summary of the membrane distribution of Cu (blue), Fe (red) and Zn (purple) transporters localized in plants. (From Grotz and Guerinot, 2006. Copyright 2006, with permission from Elsevier.)...

The cross-validated r2 values for these improved models were 0.627 and 0.776, respectively. The models implied that the brain favors cationic compounds over phospholipids membranes. Although log iam offered no advantage in these models over log P(Xt in predicting log BB ratios of the drugs (in particular because log P0ct can be calculated with sufficient accuracy), it appeared to provide a better model than log Poet for the membrane distribution of the ionized compounds. 

Provided a better model for membrane distribution of ionized compounds and concluded that brain favors cationic compounds over phospholipid membranes. 

Wieland S, Schubert R, Peschka-Siiss R. Asymmetric membrane distribution of phosphatidylserine in different liposomal preparations. J Liposome Res 1999 9(4) 477-489. 

Baumrucker, C. R. 1979. Gamma-glutamyl transpeptidase of bovine milk membranes distribution and characterization. J. Dairy Sci. 62, 253-258. 

Tab. 2.5 Parameter values derived from regression analysis of membrane distribution data. (Reprinted from ref. 45 with permission from the American Chemical Society)...

All identified TLRs are type I transmembrane proteins, whose intracellular domains contain regions homologous to the intracellular domains of IL-1R and are referred to as TIR domains (Takeda et ah, 2003). These intracellular domains are able to trigger signalling pathways known to activate the nuclear factor kappa B (NF-kB) (Medzhitov et ah, 1998 O Neill, 2000), which in turn leads to the secretion of pro-inflammatory cytokines such as TNF-a, IL-6 and IL-8. The membrane distribution of TLRs as well as their intracellular trafficking has only now beginning... 

A useful extension of this method consists in assuming that the membrane acquires a Boltzmann-like distribution of type (B.5) even for an arbitrary, nonharmonic potential /( ), which has a minimum at u = 0 [24,25]. When an external pressure Peat is applied to the undulating membrane, the relevant statistical potential is the enthalpy hill) = /(ii) + pextu and the membrane distribution is provided by ... 

Liposomes have aroused interest in a great variety of areas from biochemistry and molecular biology to cosmetics and food technology. One of the most salient applications of liposomes has been promoted by their high similarity to natural cell membranes, for which they are extensively used as substitutes in medical and pharmaceutical research. Since their inception, liposomes have often been used as models for studying the nature of cell membranes, the structure and functions of which they can mimic quite closely. One example is the determination of membrane distribution coefficients of drugs with a view to estimate their ability to penetrate cells. Interactions between analytes and phospholipid membranes depend on the characteristics of both the analytes and the membrane. 

Flip-flop 2. Although proteins rarely if ever flip-flop across a membrane, distribution of membrane lipids between the membrane leaflets is not absolute except in the case of glycolipids. Why are glycosylated lipids less likely to flip-flop ... 

Knickelbein, R. G Aronson, P, S., and Dobbins, J. W. (I9ftft). Membrane distribution of sodium -hydrogen and chloride-bicarbonate exchanges in crypt and villus cell membranes from rabbit ileum. /. Cbn. Iniwsl. 82,2158-2163. 

Proximal tubule cells in culture should have retained functional attributes such as (1) polar architecture and junctional assembly of epithelia and correct membrane distribution of enzymes and transport systems (2) vectorial transport of solutes and water, manifested by the formation of domes when cultured on solid supports [81] and the generation of transepithelial electrophysiological properties [82, 83] due to the expression of proximal tubule specific claudins 2- and 10 [84, 85] (3) cellular uptake of xenobiotics from either the apical or basolateral side, as observed in vivo and (4) expression of nephron segment-specific characteristics, i.e., distinct expression of differentiation markers, metabolic and transport properties, and hormone responsiveness. Such markers include the expression of the brush border enzymes alkaline phosphatase, leucine aminopeptidase, and y-glutamyl transferase [4, 86], In addition, proximal tubule cells should possess Na+,K+-ATPase activities, Na+-dependent glucose, and p-aminohippurate transport. Proximal tubule cells increase cAMP levels in response to parathyroid... 

Lujdn R, Roberts JDB, Shigemoto R, Ohishi H, Somogyi P (1997) Differential plasma membrane distribution of metabotropic glutamate receptors mGluRla, mGluR2 and mGluRS, relative to neurotransmitter release sites. J Chem Neuroanat 75 219-241. 

As has been shown for FPR and other receptors diffusion of a receptor protein may be restricted by interaction with the membrane skeleton [5,50]. On the other hand, interaction of G proteins with cytoskeletal elements has also been demonstrated providing for a means to also control G protein distribution in the plasma membrane (for review see [57]). An intriguing idea explaining distinct membrane distribution of G proteins has been put forward by Rodbell and coworkers who observed polydisperse forms of G proteins caused by polymerization of G subunits in analogy to tubulin [58,59]. Formation of these large molecular complexes would result in restricted mobility of the G proteins and could serve as an explanation for membrane domains in neutrophils that are enriched in G proteins (see above). 

It may be observed with a tantalizingly spurious cell-membranous distribution in foci of melanomas that border zones of geographic necrosis however, this pattern of labeling is artifactual and should be disregarded. Purely cytoplasmic reactivity for EMA is similarly discounted interpretatively. 

D2-40, a clone of podoplanin, is a recently developed commercially available antibody directed against the M2A antigen, a 40,000-kD sialoglycoprotein associated with germ cells and lymphatic endothelium. Chu and colleagues evaluated 53 cases of mesothelioma, 28 cases of reactive pleural tissue, 30 cases of pulmonary adenocarcinoma, 35 cases of renal cell carcinoma, 26 cases of ovarian serous carcinoma, 16 cases of invasive breast carcinoma, 11 cases of prostatic adenocarcinoma, and 7 cases of urothelial carcinoma. The authors found D2-40 expression in 51 of 53 (96%) mesotheliomas, 27 of 28 (96%) reactive pleural tissues, and 17 of 26 (65%) ovarian serous carcinomas. They did not find D2-40 in the other tumors examined. The authors also observed that the neoplastic cells immunostained in a cell membrane distribution. 

In addition to anticancer effects, tocotrienol-rich fractions of palm oil have hypocholesterolaemic effects in humans and offer protection against heart diseases (Qureshi el al. 1991 Serbinova el al. 1993). Tocotrienols differ from tocopherols in the degree of saturation of the side chains the prenyl side chain is considered to be responsible for the differential membrane distribution and metabolism of tocotrienols in comparison to tocopherols. Full investigations into the role and mechanisms of each tocotrienol and their interactions with other minor components, such as carotenoids, in inhibiting cancer development, as well as conferring protection against other age-related diseases, are now important areas of research. 

Collectively known as vitamin E, tocotrienols are identical in structure to tocopherols except for the degree of satmation in their side chain. The prenyl side chain of tocotrienol has been postulated to be responsible for the differential membrane distribution and metabolism of tocotrienols when compared with tocopherols. Fntnre investigations need to examine the molecular mechanism of action of tocotrienols in order to achieve a more comprehensive understanding of their complex bnt beneficial effects on cancer. 

P.A. Siegenthaler A. Bawyler (1966) Acyl lipids in thylakoid membranes distribution and involvement in photosynthetic functions. In fiicyclopedia of Plant Physiology, New Series, vol. 19 (L.A. Staehelin and C.J. Amtzen, eds), Springer-Verlag, Berlin, pp. 693-705. 

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