Lipid lamellae normal structure

FIGURE 28.1 Normal structure ofthe lipid lamellae in the intercellular space. Shown are three Landmann units... 

The Landmann-unit structure of intercellular lipid lamellae is illustrated in Figure 28.1. This structure is found throughout nearly all of the normal SC. Swartzendruber et al. proposed a plausible molecular model that accounts for the electron-lucent and electron-dense lamellar structure of the Landmann unit.10 These Landmann units are dynamic in nature. At least in the inner and middle SC they are altered by age,19 disease,8 11 20-22 and hormonal status23,24 by experimental solvent treatment25-27 and topical inhibitor treatment.28,29 They are known to reform spontaneously following solvent extraction,5,26 and topical application of certain lipids is also reported to effect lamellar repair and barrier improvement.29-33... 

It is commonly known that lipids, carbohydrates, and glycolipids are present in the Golgi apparatus (27). The determination of the components that react with the ZIO mixture was carried out by removing each component from tissues before incubation in the ZIO mixture. After lipid extraction by acetone (14), chloroform-methanol (15), or propylene oxide (27), no osmium-zinc precipitates could be detected in structures that normally reacted with ZIO. Blumcke et al. (15) summarized the nature of the lipids that react with the ZIO mixture as follows lipids and lipoproteins of cell membranes, neutral fat droplets (41), and lipid globules of type II pneumocytes and alveolar macrophages were, however, not as electron dense as the normally reactive lamellae containing highly unsaturated fatty acids. 

Calcium plays multiple roles in plant physiology and a deficiency of calcium shows up early and in dramatic ways in plant appearance. Calcium is a constituent of cell walls in the form of calcium pectate. The middle lamella is composed mainly of calcium and magnesium pectates (56). Calcium also plays a role in the formation of cell membranes and lipid structures (57)- Calcium in small amounts is pecessary for normal mitosis and it also plays a role as an activator for numerous enzymes (58). Calcium is thought to play a role in carbohydrate translocation and somehow in the development of mitochondria (59). 

In Section II,A, we consider the types of spectra expected for rapid anisotropic motion within a bilayer superstructure (Fig. 6A). It has bwn known for some time that certain lipids will form a completely different type of structure in which the molecules project radially from the center of a cylinder (Fig. 6B Luzzati and Husson, 1962). As mentioned in Section II,B, rapid lateral diffusion within a bilayer phase only affects P-NMR line shapes if the lamellae enclose a particle of small radius. The cylinders in a hexagonal phase have a very small radius, and therefore lateral diffusion about the cylinder axis can cause further averaging of tensor components. The unique axis of the system now becomes the axis of the cylinder, and thus we label its chemical-shift component ap. However, noticing that along this axis the field would be roughly normal to the fatty acyl chains, we would expect the value of this chemical shift to be similar to. On the other hand. 

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