Membrane family

Hyperlipidaemias are conditions where levels of LDL cholesterol are raised relative to HDL levels. They can be primary or secondary to other conditions such as diabetes or hypothyroidism. About 5% of cases are due to a hereditary condition where there is a deficiency of LDL receptors on cell membranes (familial hyperlipidaemia). 

DPMs can also be formulated as composite materials. In this concept, the contact of the two phases at the nanoscale provides materials with improved ionic and electronic conductivities. Examples of composite DPMs encompass the combination of two perovskite and fluorite phases for oxide ion conduction, the latter usually relying on the formula Cei >,Y >,02-5 (Y = Gd, Sm) [11-14]). Perovskites can also be hybridized with metal phases or cermets (most often based on Ni) for promoting the electronic conductivity and stability of cerates for H2 permeation [15-18]. Mass transfer within this membrane family can be described using either a unified permeation model for the two phases as for single-phase membranes or by including the contribution of each phase (Figure 14.2d). 

Eighteen different membrane polymers can be attributed to four synthetic and to one cellulosic membrane family. They will be described shortly in the following and characterized by features that outline their specific individual advantages or disadvantages. Table 13.2 depicts an actualized list of polymers used for dialysis membranes and the appropriate manufacturers of dialyzers. Their characteristics will be discussed below. 

Membrane Families, Their Main Features and Specific Properties ... 

The high EWs of the first Nafion membranes family limited their use in fuel cells and prompted the development of the Dow membrane. This membrane is structurally and morphologically similar to the Nafion membrane, but differs with respect to its EWs, which are typically in the 800 to 850 range, and have shorter size chains (z = 0 for Dow and z = 1 for Nafion) (Utracki and Weiss, 1989). The Dow membranes are a short side chain perfluorinated ionomer whereas the Nafion membranes are the long side chain perfluorinated ionomer. The specific conductance of 800 and 850 EW experimental membranes has been reported as 0.20 and 0.12 Q cm", respectively (Savadogo et al, 1995). It must be pointed out that the Dow monomer is more complicated to elaborate than the DuPont monomer. Therefore, the synthesis of the Dow epoxy is more complicated than that of the Nafion, which is a commercially available material (Savadogo et al, 1995). 

G-Protein Coupling. The heterotrimeric guanosine triphosphate (GTP) binding proteins, known as G-proteins, are a principal family of proteins serving to couple membrane receptors of the G-protein family to ionic and biochemical processes. This topic is reviewed in References 63—67. 

Polyethers. Antibiotics within this family contain a number of cycHc ether and ketal units and have a carboxyHc acid group. They form complexes with mono- and divalent cations that ate soluble ia aoapolar organic solvents. They iateract with bacterial cell membranes and allow cations to pass through the membranes causiag cell death. Because of this property they have been classified as ionophores. Monensia, lasalocid, and maduramicia are examples of polyethers that are used commercially as anticoccidial agents ia poultry and as growth promotants ia mmiaants. 

FIG. 22-55 Typical capital-cost schematic for membrane equipment showing trade-off for membrane area and mechanical equipment. Lines shown are from families for parallel hues showing hmiting costs for membrane and for ancillary equipment. Abscissa Relative membrane area installed in a typical membrane process. Minimum capital cost is at 1.0. Ordinate Relative cost. Line with positive slope is total membrane cost. Line with negative slope is total ancillary equipment cost. Curve is total capital cost. Minimum cost is at 1.0. 

Membrane Chemistry Three chemical families dominate the RO-NF membrane industry. Many other products are made on a small scale, and the field continues to attract significant R D resources. But three types command most of the market. 

Capital Costs A typical medium-scale RO seawater plant might produce 0.25 mVs (6 MGD). For a plant with an open sea intake, seawater salinity of 38 g/1, and conversion of 45 percent, the overall cost woiild be 26.5 miUiou (1996). A capital breakdown is given in Table 22-18. Capital charges are site specific, and are sensitive to the salinity of the feed. A plant of this size would likely contain six trains. For seawater RO, the Best estimate for the slopes of the family of lines in Fig. 22-55 is —0.6 for the equipment and 0.95 for the membranes. Capital charges, shown in TaBle 22-19, usually dominate the overall economics the numbers presented are only an example. Seawater economics are based on Shields and Moch, Am. Desalination Assn. Conf. Monterey CA (1996). 

In this chapter we describe some examples of structures of membrane-bound proteins known to high resolution, and outline how the elucidation of these structures has contributed to understanding the specific function of these proteins, as well as some general principles for the construction of membrane-bound proteins. In Chapter 13 we describe some examples of the domain organization of receptor families and their associated proteins involved in signal transduction through the membrane. 

The polypeptide chain of Src tyrosine kinase, and related family members, comprises an N-terminal "unique" region, which directs membrane association and other as yet unknown functions, followed by a SH3 domain, a SH2 domain, and the two lobes of the protein kinase. Members of this family can be phosphorylated at two important tyrosine residues—one in the "activation loop" of the kinase domain (Tyr 419 in c-Src), the other in a short... 

A completely separate family of conducting polymers is based on ionic conduction polymers of this kind (Section 11.3.1.2) are used to make solid electrolyte membranes for advanced batteries and some kinds of fuel cell. 

Plant cells contain a unique family of organelles, the plastids, of which the chloroplast is the prominent example. Chloroplasts have a double membrane envelope, an inner volume called the stroma, and an internal membrane system rich in thylakoid membranes, which enclose a third compartment, the thylakoid lumen. Chloroplasts are significantly larger than mitochondria. Other plastids are found in specialized structures such as fruits, flower petals, and roots and have specialized roles. 

FIGURE 1.2 Schematic diagram of potential drag targets. Molecules can affect the function of numerous cellular components both in the cytosol and on the membrane surface. There are many families of receptors that traverse the cellular membrane and allow chemicals to communicate with the interior of the cell. 

The ABC-transporter superfamily represents a large group of transmembrane proteins. Members of this family are mainly involved in ATP-dependent transport processes across cellular membranes. These proteins are of special interest from a pharmacological point of... 

A comprehensive summary of these enzyme families is beyond the scope of this chapter, but a few examples are worth emphasis. The Class I adenylyl cyclases of the enterobacteria Salmonella typhimurium, Yersinia pestis, and Escherichia coli are membrane bound yet sequences do not give ready evidence of typical... 

Although the 3 - and 5 -polyphosphate derivatives mentioned above exhibit exquisite inhibitory potency these compounds are not cell permeable. To take advantage ofthepotency of such derivatives for studies with intact cells and tissues, there are two possibilities. One is chemically to protect the phosphate groups from exonucleotidases that also allows the compound to transit the membrane intact. The other is to provide a precursor molecule that is cell permeable and is then metabolized into an inhibitor by intracellular enzymes. The general term for such a compound is prodrug nucleotide precursors are also referred to as pronucleotides. Families of protected monophosphate derivatives were synthesized, based on (3-L- and 3-D-2, 5 -dd-3 -AMP, 3-L-2, 3 -dd-5 -AMP, and the acyclic 9-substituted adenines, PMEA and PMPA. Protective substituents were (i) -( -pivaloyl-2-thioethyl) ... 

---