Amphipathic, amphiphilic

These AChE forms differ in solubility and mode of membrane attachment rather than in catalytic activity. One class of molecular forms exists as homomeric assemblies of catalytic subunits that appear as monomers, dimers or tetramers (Fig. 11-7). These forms also differ in hydrophobicity, and their amphiphilic character arises from either exposure of an amphipathic helix or post-translational addition of a glycophospholipid on the carboxyl-terminal amino acid. The glycophospholipid allows the enzyme to be tethered on the external surface of the cell membrane. 

The out-of-plane orientation of chromophores can be more easily controlled in LB films as compared with the in-plane orientation. Many chromophores are known to show anisotropic orientation in the surface normal direction. The molecular structure of chromophores and their position in amphiphile molecules, the surface pressure, the subphase conditions are among those affect their out-of-plane orientation. The out-of-plane orientation has been studied by dichroic ratio at 45° incidence, absorbance ratio at normal and 45° incidence, and incident angle dependence of p-polarized absorption [3,4,27,33-41]. The evaluation of the out-of-plane orientation in LB films is given below using amphipathic porphyrin (AMP) as an example [5,10,12]. 

The cahnodulin-binding peptides assume random coil structures in solution, but in the presence of calmodulin they form amphipathic or amphiphilic (containing both polar and nonpolar residues) helices. All of these peptides have nanomolar (very high) affinities for calmodulin. Table 6.9 shows the primary amino acid sequence of some of the cahnoduUn-binding peptides, and it is informative to compare them as they are discussed in the following material. 

It follows from study of the kinetics of transfer of ions across the phase boundary between two immiscible electrolyte solutions (see chapter 9) that ion-exchanger ions, where the ion is as nearly as possible symmetrically surrounded by hydrophobic groups on all sides, are especially suitable. Amphiphilic (amphipathic) substances, in whose molecules the hydrophobic part is separated from the hydrophilic part, are less suitable because they have a tendency to become adsorbed on the membrane/water phase boundary, thus retarding ion transfer across this boundary. 

Molecules that contain both polar and apolar groups are called amphipathic or amphiphilic. This group includes soaps (see p.48), phospholipids (see p. 50), and bile acids (see p. 56). 

Nutrients. Amphipathic lipids are used by cells to build membranes (see p. 214). Typical membrane lipids include phospholipids, glycolipids, and cholesterol. Fats are only weakly amphiphilic and are therefore not suitable as membrane components. 

A special group of lipids that possess both hydrophilic and hydrophobic (lipophilic) parts are termed as amphiphiles or amphipathics and are also referred to as surfactants. They adsorb at surfaces or interfaces and change the interfacial free energy associated with the building of an interface. A surfactant molecule consists of two distinct chemical groups (i) the head which is hydrophilic (water-loving) and (ii) the tail which is hydrophobic (water-fearing). 

Some compounds, like short-chain fatty acids, are amphiphilic or amphipathic, i.e., they have one part that has an affinity for the nonpolar media (the nonpolar hydrocarbon chain) and one part that has an affinity for polar media such as water (the polar group). The energetically most favourable orientation for these molecules is at surfaces or interfaces so that each part of the molecule can reside in an environment for which it has the greatest affinity (see Figure 3.18). These molecules that form... 

Lipid bilayer Amphipathic (or amphiphilic) molecules contain both hydrophilic (water-... 

Lipids (fats) are generally insoluble in water but are soluble in organic solvents. Solubility characteristics depend on structural features those fats that have no polar residues are least water soluble, and they exist away from the aqueous environments of the organism (e.g., cholesterol esters and triglycerides). Others have hydrophilic along with hydrophobic residues. These are called amphipathic substances (also amphiphiles), and they may exist at the interface between aqueous and nonaqueous environments (e.g., phosphoglycerides). 

Many types of lipid are said to be amphiphilic, meaning they consist of two parts—a nonpolar hydrocarbon region and a region that is polar, ionic, or both. (The term amphiphilic has tended to replace amphipathic, used formerly.)... 

The second possibility of gating MS channels by bilayer tension takes into consideration changes in intrinsic bilayer curvature as a possible trigger for the channel opening (Fig. 3). Experiments on bacterial MS channels suggested that a diverse group of substances with amphipathic or amphiphilic properties... 

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