Fibrous intracellular

An intracellular fibrous system exists of filaments with an axial periodicity of 21 nm and a diameter of 8-10 nm that is intermediate between that of microfilaments (6 nm) and microtubules (23 nm). Four classes of intermediate filaments are found, as indicated in Table 49-13. They are all elongated, fibrous molecules, with a central rod domain, an amino terminal head, and a carboxyl terminal tail. They form a structure like a rope, and the mature filaments are composed of tetramers packed together in a helical manner. They are important structural components of cells, and most are relatively stable components of the cytoskeleton, not undergoing rapid assembly and disassembly and not... 

Intracellular space Fibrous protein ( 65-70%), nonfibrous (soluble) protein ( 5-10%) 75... 

The fibrous network was identified as being composed of two elaborated membrane systems, the system of transverse tubules which are narrow invaginations of the plasma membrane and the sarcoplasmic reticulum which constitute an intracellular complex network of membranous tubules and cistemae (Fig. la)17. The transverse tubules have been identified as the structures along which the action potential is conducted inwards. 

The skin is two discrete tissue layers, both polymeric but differing in protein composition, morphology, and thickness (I, 2) (Figure 1). Epidermis, the outer layer, is cellular and is composed primarily of the intracellular fibrous protein keratin associated with lipids. In contrast,... 

The detailed chemistry of the stratum corneum is complicated by the membrane s composition, formation, and structure. Some gross chemical characterizations have determined the primary chemical components of the tissue which are shown in Table I (29). The tissue is primarily cellular with approximately 10% extracellular components which are lipid and mucopolysaccharides. The bulk of the tissue is densely packed intracellular fibrous protein associated with lipids, resulting in a dry general body corneum density of 1.35-1.40 gm/cm as determined by a gas displacement technique (30). 

The morphological location of the fibrous protein principally responsible for the deformation and viscoelastic behavior is uncertain. Both the cell membrane and intracellular regions are composed of fibrous proteins which differ considerably in amino acid composition. Since the alpha-keratin within the cells shows few orientation properties until high elongations, it has been suggested that the membrane proteins determine the viscoelastic behavior at low deformations (84). 

In a search for an understanding of the range of solubility of intracellular fibrous proteins we see that the principal types are displayed in the fibrinogen-fibrin system, where, of course, study of the factors involved is fairly well advanced. 

C oskalaton a three-dimensional network of fibrous proteins in the cytoplasm which provide structural support, motility and a scaffolding along which intracellular bodies can be moved. The C. has 3 distinct components microtubules (25 nm diameter), microfilaments (6-8 nm) and intermediate filaments (10 nm). 

Traub hypothesizes that the Ca -activated proteinase associated with IF may convert the proteins to a form which does not readily polymerize, but which binds more readily to histones. The normal intracellular concentration of Ca is far too low to activate the proteinase, but it is known that endocytosed vesicles and other membrane structures may release Ca. Thus the local concentration could be high enough to activate the proteinase and to cause conversion of the IF protein from the fibrous to the signal form. [P.Traub, Intermediate Filaments (Springer, Heidelberg, 1985)]... 

This accounts for about 2/3 of the chloride content of proximal tubule cells. The discrepancy between the active electrometric [Cl ] of 18.7 mM and the total intracellular chloride of 32.1 mM may be accounted for by one of three possibilities. First, a non-uniform distribution of chloride within different intracellular compartments. The lateral intercellular space which may not be readily penetrated by inulin is a region of hypertonicity rich in chloride. Second, 1/3 of the intracellular chloride may be bound to proteins or other macromolecules or fibrous elements. Third, cells of distal tubules may have a higher intracellular chloride (Conway et dl,y 1946) than those of proximal tubules. 

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