Distribution in eukaryotic cells

Actin (Mr = 41,800) is widely distributed in eukaryotic cells, often being the most abundant protein, and commonly making up about 10 percent of the total cell protein. The protein is highly conserved with only 17 of the 375 amino acids different between slime mold actin and rabbit muscle actin. Monomeric actin is usually referred to as globular or G-actin while the polymer, filamentous actin, is termed F-actin. 

We have found that the ecto-ATPase is optimally stimulated by Mn at concentrations of 3 x 10" or below, but we have also observed some exceptions (for instance, in mouse neuroblastoma where 10 M Ca was most effective and Mn did not stimulate). Mn concentrations in excess of 3 x 10 M are inhibitory. The ecto-ATPase seems widely distributed in eukaryotic cells. There has been an earlier report that the enzyme was not present on the surface of intact neurons (CUMMINS HYDEN, 1962) but it certainly is present on the surface of intact neuroblastoma cells (TRAMS 6e LAUTER, 1974 STEFANOVIC et ad, 1976b), Conventional sulfhydryl compounds or inhibitors have little effect on the enzyme and ouabain is not inhibitory. We have found that ecto-ATPase of cultured CNS cells was inhibited by certain phenothiazine derivatives. Micromolar concentrations of thiazines and tricyclic antidepressants were inhibitory in rat leukocytes (MEDZIHRADSKY et, 1975). There has been one report that adipocyte membrane Mg ATPase was markedly stimulated by insulin and by Concanavalin A (JARRETT Sc SMITH, 1974). ... 

A large number of discrete, highly conserved, and small stable RNA species are found in eukaryotic cells. The majority of these molecules are complexed with proteins to form ribonucleoproteins and are distributed in the nucleus, in the cytoplasm, or in both. They range in... 

The main component of E. coli—as in all cells—is water (70%). The other components are macromolecules (proteins, nucleic acids, polysaccharides), small organic molecules, and inorganic ions. The majority of the macromolecules are proteins, which represent ca. 55% of the dry mass of the cell. When a number of assumptions are made about the distribution and size (average mass 40 kDa) of proteins, it can be estimated that there are approximately 250000 protein molecules in the cytoplasm of an E. coli cell. In eukaryotic cells, which are about a thousand times larger, it is estimated that the number of protein molecules is in the order of several billion. 

Results of cell biological, biochemical, and immunological research of the past decades have revealed that glycosylation is a very common posttranslational modification of proteins in eukaryotic cells [1]. The carbohydrate portions of glycoproteins obviously play important roles in the organized distribution of these macromolecules within the cells and... 

Describe the typical distribution pattern of RNA and DNA in bacterial cells and in eukaryotic cells. 

All of the oncosphere antigens cloned to date contain either one of two copies of a predicted Fnlll domain. These domains are widely distributed in eukaryotic proteins and occur also in some prokaryotic proteins (Bork and Doolittle, 1992). Approximately 2% of animal proteins include Fnlll domains. Many, but not all, of these proteins are extracellular and some have roles as adhesins. The structure of this 100 amino acid domain is highly conserved and consists of two layers with three p strands in one plane and four p strands in another (Potts and Campbell, 1996). Overall, amino acid sequence identity between different Fnlll domains is low, even between Fnlll repeat domains within fibronectin itself (Plaxco et al., 1997). Nevertheless, certain residues are highly conserved and maintain the tertiary structure of the proteins (Bork and Doolittle, 1992). Other conserved motifs such as an Arg-Gly-Asp (RGD) motif within a loop of some Fnlll domains is associated with proteins having cell adhesion properties, as discussed above (Ruoslahti and Pierschbacher, 1987 D Souza et al., 1991). 

Cell fractionation studies of five strains of cyanobacteria indicate that MAAs are located primarily (>90%) within the cytoplasm and not the cell sheaths, walls, or membranes.132 Extracellular placement of MAAs does occur in some cyanobacterial species that posses cellular sheath layers.134135 Extracellular MAAs are covalently bonded to oligosaccharide molecules embedded in the cyanobacterial sheath matrix and provide substantial protection to prevent photobleaching of chlorophyll within the cell. Intracellular or extracellular distributions of MAAs in eukaryotic cells have not been investigated. Based on the high MAA concentrations of Phaeocystis antarctica colonies, it has been suggested that MAAs are associated with the extracellular mucopolysaccharide matrix of the colony.125 This may be a more common phenomenon than currently recognized, and future research efforts will be necessary to further document extracellular occurrence of MAAs in cyanobacteria and algae. 

This simple calculation indicates that if H+ were passively distributed across the plasma membrane, and for a mean membrane potential of-60 mV, intracellular pH values (pHi) would be expected to be 1 pH unit lower than the external pH values (pHo). Numerous experiments performed on a large variety of cells indicate, however, that pHi values are usually close to pHo values, or slightly below (Roos and Boron, 1981). This implies that H+ ions are not passively distributed across the plasma membrane and that H+ pumps drive H+ out of equilibrium. Different H+ pumps have been identified in eukaryotic cells an ubiquitous Na+/H+ exchanger, and pumps that have a more restricted cellular distribution. These are (H+)ATPases,... 

A FIGURE 5-30 Schematic depiction of the distribution of cytoskeletal filaments in eukaryotic cells and bacterial cells. 

Protein disulfide isomerase (PDI), a homo-dimeric protein (Mr 110 kDa) widely distributed across eukaryotic cells. PDI catalyzes the isomerization and rearrangement of disulfide bonds in the endoplasmic reticulum. Furthermore, S-denitrosation activity of PDI has been described. Recently, a direct, continuous, sensitive assay of PDI based on fluorescence self quenching has been described [B. Wflkin-son, H. F. Gilbert, Biochim. Biophys. Acta... 

Hilz H, Bredehorst R, Adamietz P, Wielckens K (1982) Subfractions and subcellular distribution of mono(ADP-ribosyl) proteins in eukaryotic cells. In ADP-ribosylation reactions, chap 11. Academic Press, London New York... 

The nervous system has proven useful for the study of another timely problem that of intracellular distribution of enzymes and substrates of structural lipid formation and degradation in eukaryotic cells and the mechanisms of their assembly into membranes. The neuron constitutes a particularly useful model, by virtue of its peculiar shape. Because its axon may be larger than the perikaryon by several magnitudes, we can take advantage of the process of axonal flow to study the rate of appearance of labeled lipid at some distance from sites of synthesis. 

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