Lipid hydrophobic area

Carotenoids are lipid-soluble terpenoids derived from the isoprenoid pathway and are located in hydrophobic areas of cells. All have a 40-carbon isoprene backbone with a variety of ring structures at one or both ends (Fig. 8.2) [25]. The carbon skeleton is derived from five-carbon isoprenoid groups and contains alternating conjugated double bonds. There are two kinds of carotenoids (Fig. 8.2) carotenes composed of carbon and hydrogen and xanthophylls composed of carbon, hydrogen, and oxygen. 

Ipsen, J. H., Mouritsen, O. G. and Bloom, M. (1990). Relationships between lipid membrane area, hydrophobic thickness and acyl-chain orientational order. The effects of cholesterol. Biophys. J. 57 405. 

This order-order transition is well-rationalized by the concept of the CPP expressed as vlAl, which is the ratio between the volume of the hydrophobic lipid tail, V, and the product of the cross-sectional lipid head area. A, and the lipid chain length, 1. When linoleic acid is deprotonated (pH 7), the effective area A is large because of the electrostatic repulsive interactions among different hpid heads. When, however, the linoleic acid is mostly neutral (pH 2), A decreases and the CPP increases, promoting the transition from flat to reverse (water-in-oil) interfaces and inducing a bicontinuous cubic reverse columnar hexagonal transition. 

The NaK-ATPase activity which is initiated in response to acetylcholine can be monitored by measurement of the 3-fold increase in the rate of respiration which it evokes. This increase in the respiratory rate is blocked by ouabain, which specifically blocks NaK-ATPase activity, and by atropine, which specifically blocks acetylcholine receptors. In the salt gland, an almost maximal increase in secretory NaK-ATPase activity occurs in response to O.lyM acetylcholine and in this tissue, in contrast to the pancreas, the breakdown of phosphatidylinositol, as measured by the amount resynthesized after addition of atropine to stimulated tissue, also occurs almost maximally at this same low concentration of acetylcholine (Table 5). These observations lead me to propose that in the salt gland cell, the function of stimulated phosphatidylinositol breakdown, and of its resynthesis during the reversion to the unstimulated state, is to exert on-off control of the activity of the secretory NaK-ATPase molecules. These are "turned on" when this tissue is stimulated, and are "turned off when the tissue reverts to the non-secreting state. A simple mechanism for this might be that when the responsive lipid molecules are in the phosphatidylinositol form, an active site of the secretory NaK-ATPase is buried in a hydrophobic area of the membrane, and that when the phosphatidylinositol is broken down, this results in a membrane change... 

It follows from the second law of thermodynamics that the optimal free energy of a hydrocarbon-water mixture is a function of both maximal enthalpy (from hydrogen bonding) and minimum entropy (maximum degrees of freedom). Thus, nonpolar molecules tend to form droplets with minimal exposed surface area, reducing the number of water molecules affected. For the same reason, in the aqueous environment of the hving cell the hydrophobic portions of biopolymers tend to be buried inside the structure of the molecule, or within a lipid bilayer, minimizing contact with water. 

In addition to the self-spreading lipid bilayer, it was also found that a lipid mono-layer showed similar spreading behavior on a hydrophobic surface (Figure 13.6) [51]. By fabricating an appropriate hydrophobic surface pattern, the spreading area and direction can be easily controlled. For both the self-spreading bilayer and monolayer, non-biased molecular transportation is an important key concept for the next generation of microfiuidic devices. 

All of the aliphatic and aromatic hydrophobic residues often are located at the interior of protein molecules or in areas that interact with other non-polar structures such as lipids. They usually form the hydrophobic core of proteins and are not readily accessible to water or other hydrophilic molecules. 

Photosystem I is a membrane pigment-protein complex in green plants, algae as well as cyanobacteria, and undergoes redox reactions by using the electrons transferred from photosystem II (PS II) [1], These membrane proteins are considered to be especially interesting in the study of monomolecular assemblies, because their structure contains hydrophilic area that can interact with the subphase as well as hydrophobic domains that can interact either with each other or with detergent and lipids [2], Moreover, studies with such proteins directly at the air-water interface are expected to be a valuable approach for their two-dimensional crystallization. 

Influence of subphase temperature, pH, and molecular structure of the lipids on their phase behavior can easily be studied by means of this method. The effect of chain length and structure of polymerizable and natural lecithins is illustrated in Figure 5. At 30°C distearoyllecithin is still fully in the condensed state (33), whereas butadiene lecithin (4), which carries the same numEer of C-atoms per alkyl chain, is already completely in the expanded state (34). Although diacetylene lecithin (6) bears 26 C-atoms per chain, it forms both an expanded and a condensed phase at 30°C. The reason for these marked differences is the disturbance of the packing of the hydrophobic side chains by the double and triple bonds of the polymerizable lipids. At 2°C, however, all three lecithins are in the condensed state. Chapman (27) reports about the surface pressure area isotherms of two homologs of (6) containing 23 and 25 C-atoms per chain. These compounds exhibit expanded phases even at subphase temperatures as low as 7°C. 

Cationic amphiphiles 2Ci8-glu-N spread on pure water, in the solution of 10 xM DNA containing 10 xM intercalating dyes (proflavine). The dye-intercalated DNA anions were expected to adsorb to the cationic lipid mono-layer due to electrostatic interactions and was transferred to a hydrophobized glass plate at a surface pressure of 35 mN m at 20 °C. From a moving area of a barrier, two layers of the monolayer were confirmed to be transferred in each one cycle (Y-type deposition). When the QCM plate was employed as a transfer plate, the transferred mass could be calculated from frequency decreases (mass increase on the QCM) [29-31]. It was confirmed that 203 10 ng of two lipid monolayers and 74 5 ng of DNA strands were transferred on to the substrate per dipping cycle, which means ca. 95% of the monolayer area was covered by DNA molecules. 

Orally administered drugs partition into the lipid bilayer in the process of diffusing across the apical and basolateral membranes of the intestinal brush border cells into the blood, as illustrated in Figure 2. About 1800 such drugs are commercially available. A small surface area of the polar parts of the drug molecule generally favors entry into the hydrophobic interior of... 

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