Cell cytosol

The specific role of vitamin A in tissue differentiation has been an active area of research. The current thinking, developed in 1979, involves initial dehvery of retinol by holo-B >V (retinol-binding protein) to the cell cytosol (66). Retinol is then ultimately oxidized to retinoic acid and binds to a specific cellular retinoid-binding protein and is transported to the nucleus. Retinoic acid is then transferred to a nuclear retinoic acid receptor (RAR), which enhances the expression of a specific region of the genome. Transcription occurs and new proteins appear during the retinoic acid-induced differentiation of cells (56). 

Nuclear factor of activated T cells cytosolic NFATc... 

Nuclear Factor of Activated T Cells Cytosolic NFATc... 

The 25-OH-D Is further metabolized In the kidney to 1,25 dlhydroxycholecalclferol (1,25(OH)2D) which Is considered to be the major physiologically Important, tissue-active metabolite of vitamin D. It circulates In extremely low concentrations (< 100 pg/ml of serum). Assay of 1,25(OH)2D Is extremely tedious. It Is done by competitive binding technique using a combined Intestinal cell cytosol and chromatin binding system, biosynthetic 3h-1,25(OH)2D3 as labeled ligand and synthetic 1,25(0H)2D3 as standard (31). 

Figure 8.5 The synthetic pathway for noradrenaline. The hydroxylation of the amino acid, tyrosine, which forms dihydroxyphenylalanine (DOPA) is the rate-limiting step. Conversion of dopamine to noradrenaline is effected by the vesicular enzyme, dopamine-P-hydroxylase (DpH) after uptake of dopamine into the vesicles from the cell cytosol...

Studies of release of noradrenaline from sympathetic neurons provided the first convincing evidence that impulse (Ca +)-dependent release of any transmitter depended on vesicular exocytosis. Landmark studies carried out in the 1960s, using the perfused cat spleen preparation, showed that stimulation of the splenic nerve not only led to the detection of noradrenaline in the effluent perfusate but the vesicular enzyme, DpH, was also present. As mentioned above, this enzyme is found only within the noradrenaline storage vesicles and so its appearance along with noradrenaline indicated that both these factors were released from the vesicles. By contrast, there was no sign in the perfusate of any lactate dehydrogenase, an enzyme that is found only in the cell cytosol. The processes by which neuronal excitation increases transmitter release were described in Chapter 4. 

There is also some evidence for subtypes of COMT but this has not yet been exploited pharmacologically. Certainly, the majority of COMT is found as soluble enzyme in the cell cytosol but a small proportion of neuronal enzyme appears to be membrane bound. The functional distinction between these different sources of COMT is unknown. COMT inhibitors also exist (e.g. pyrogallol), mostly as catechol derivatives, but so far, most have proved to be highly toxic. Only recently have drugs been developed which are selective for COMT one of these agents, tolcapone, is used currently in treatment of Parkinson s disease (see Chapter 15). 

The poor activities of pectic enzymes in the cultivation medium led us to prove the cell cytosole and the cell walls for these activities. The cytosole contains only traces of polygalacturonase activity, but the suspension of cell walls established the activity which seems to be widely sufficient for yeast growth and development. The characterization of this cell wall bound enzymes will be the object of our next studies. 

Other plasminogen activator inhibitors are PAI-3, which is believed to be identical to the activated protein C inhibitor, and proteinase nexin 1, found in the renal epithelial cells, cytosol of fibroblasts, and cardiac myocytes (37, 42, 44, 45). 

Although the absence of paracellular transport across the BBB impedes the entry of small hydrophilic compounds into the brain, low-molecular-weight lipophilic substances may pass through the endothelial cell membranes and cytosol by passive diffusion [7]. While this physical barrier cannot protect the brain against chemicals, the metabolic barrier formed by the enzymes from the endothelial cell cytosol may transform these chemicals. Compounds transported through the BBB by carrier-mediated systems may also be metabolized. Thus, l-DOPA is transported through the BBB and then decarboxylated to dopamine by the aromatic amino acid decarboxylase [7]. 

Meanwhile chromodulin, stored in apo form in the cell cytosol and nucleus, is metallated by transfer of Cr(III) from the blood to insulin-dependent cells, perhaps by the metal transport protein transferrin. 

McAinsh MR, Webb AAR, Taylor JE, Hetherington AM. Stimulus-induced oscillations in guard cell cytosolic free calcium. Plant Cell 1995 7 1207-1219. 

Binary toxins are unique concerning their structure because they are comprised of two individual, nonlinked proteins represented by an enzyme component and a binding/translocation component. The two components are secreted by the bacterium and assemble upon the surface of targeted eukaryotic cells to form an active toxin complex. For this to occur, both protein components of binary toxins act in a precisely concerted manner. The binding component first engages the cell-surface receptor and then mediates translocation of enzyme compo-nent(s) from the outside of a cell, through acidified endosomes, and into the host cell cytosol where it modifies the substrate (for review see Barth ). 

Both, longitudinal and transverse relaxation of protons in tissue depend on the microstructure and on the chemical composition of several microscopic compartments. Relaxation properties are not necessarily constant for the diiferent compartments inside the cells (cytosol and cavities in cell organella) and in the extracellular space (interstitium and vessels). However, water exchange processes between the compartments are often fast enough to generate one effective relaxation time, which can be assessed by monoexponential fitting of the relaxation dependent data. 

Alice et al studied the turnover kinetics of Listeria OTonocytogenex-secreted p60 protein (a murein hydrolase) by host cell cytosolic proteasomes. J774 cells, seeded in flasks and incubated overnight in culture medium, were infected with log-phase cultures of E. monocytogenes for 30 min, washed, and incubated in culture medium for 3 h, with gentamicin (50 tg/ml) added after the first 30 min to inhibit extracellular bacterial growth. Cells then were washed and placed in methionine-free medium with spectinomycin, gentamicin, the eukaryotic protein synthesis inhibitors [cycloheximide (50 tg/mL) and anisomycin (30 tg/ml),] and 25 dVI calpain inhibitor I. After 30 min, [ S]methionine was added, and the cells were pulse-labeled for periods of 20 to 60 min. Cells... 

The energy producing reactions are coupled to carry out some other chemical reactions which are otherwise not energetically possible. ATP, ADP and AMP occur not only in cell cytosol but also in mitochondria and the nucleus. 

There has been considerable debate about how the HRVs accomplish the transfer of RNA from inside the virion into the cell cytosol. This step is crucial for productive uncoating. An important question concerns the requirement for acidification of the endosome for HRVs to release their RNA. Evidence that appeared to conflict was found in a number of studies using either entero- or rhinoviruses (35-39). This question was later addressed by experiments that specifically separated entero- and rhinovirus behavior [40]. These experiments showed that HRVs, unlike poliovirus, require a pH-lowering step for productive infection. This pH lowering is likely to occur in the endosomal compartment. It should be noted that HRV and enteroviruses have been classified historically based on their resistance to acid HRVs are acid-labile, while enteroviruses are stable in acid. Consequently, differences in behavior between the rhino- and enteroviruses in an acidic environment within the cell are not surprising. 

One remarkable difference between the cells of plants and animals is the absence in the plant cell cytosol of the enzyme inorganic pyrophosphatase, which catalyzes the reaction... 

FIGURE 20-25 Sucrose synthesis. Sucrose is synthesized from UDP-glucose and fructose 6-phosphate, which are synthesized from triose phosphates in the plant cell cytosol by pathways shown in Figures 15-7 and 20-9. The sucrose 6-phosphate synthase of most plant species is allosterically regulated by glucose 6-phosphate and P,. 

The products of lipid digestion—free fatty acids, 2-monoacylglycerol, and cholesterol—plus bile salts, form mixed micelles that are able to cross the unstirred water layer on the surface of the brush border membrane. Individual lipids enter the intestinal mucosal cell cytosol. 

Our understanding of the details of these processes will probably increase in the near future, due to the development of better techniques for the determination of intracellular [Ca2+], One example involves the use of the fluorescent indicator quin 2. This allows quantitative determination of [Ca2+] rather than the mere confirmation of increase or decrease in [Ca2+].412,413 Quin 2 binds Ca2+ with high selectivity, and its fluorescence increases more than four-fold upon saturation with Ca2". The indicator is added in a lipophilic form, the tetraacetoxymethyl ester, which is taken up by cells. Hydrolysis within the cells gives quin 2, which will then remain in the cell cytosol without binding to cytoplasmic proteins or uptake into organelles. An example of its use lies in the demonstration that release of insulin was mediated by increase in cytosolic Ca2+ produced by use of the Ca2+-ionophore ionomycin.414... 

RIPs are plant protein toxins that are able to inhibit enzymatically ribosomal activity and are therefore highly cytotoxic [98]. RIPs are taken up in the cells by means of endocytosis, and only a small fraction (5% or less) are translocated to the cytosol where the toxins inhibit the protein synthesis and eventually kill the cell. PCI may be used to increase both the efficacy and specificity of these toxins. RIPs are divided into two groups, type I and type II. Type II RIPs, like ricin, consists of two polypeptide chains, one cytotoxic A-chain with /V-glycosidase activity and one B-chain which binds to the cell surface. Type I RIPs, like gelonin, agrostin, and saporin, lack the B chain, which make them poorly transported over the cell- and intracellular membranes to the cell cytosol. Hence, the cytotoxic effect of these protein toxins is usually absent or very low. A considerable cytotoxic effect of type I RIPs has been shown in combination with PCI, both in vitro and in vivo [25, 99]. 

The L chains of CNTs block neuroexocytosis by acting in the cytosol, and therefore at least this toxin domain must reach the cell cytosol. In order to do so, the L chain... 

Ramon G, Descombey P (1925) Sur 1 immunization antitetanique et sur la production de l antitoxine tetanique Compt Rend Soc Biol 93 508-98 Ratts R, Zeng H, Berg EA, Blue C, McComb ME et al. (2003) The cytosolic entry of diphtheria toxin catalytic domain requires a host cell cytosolic translocation factor complex. J Cell Biol 160 1139-50... 

The following are discussions of four categories of ODEs, based on their location in the animal. To some degree this has functional significance, distinguishing between ODEs of the sensillum lumen (soluble or membrane bound), support cell cytosol and body surface. 

Protection should be immediately obvious when the results of a labeling experiment are examined by gel electrophoresis. A particularly clear-cut example is reproduced in Fig. 4.6 (Pomerantz et al., 1975 see also Fig. 4.4). Another instructive example can be seen in the work of Nordeen et al. (1981) in which specific labeling of glucocorticoid receptors was distinguished from a strongly but non-specifically labeled component of cell cytosol. 

Main intracellular compartments of an animal cell. Cytosol, endoplasmic reticulum, Golgi complex, nucleus, mitochondria, endosome, lysosome, and peroxisome are distinct compartments that are isolated from the rest of the cell by at least one selective membrane. 

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