Extracellular sequestration

Which mechanism predominates, intracellular or extracellular sequestration, is dependent on the organism involved. For example, uranium accumulated extracellularly as needle-like fibrils in a layer approximately 0.2 pm thick on the... 

Fig. 10.8. Simple biogeochemical model for metal mineral transformations in the mycorhizosphere (the roles of the plant and other microorganisms contributing to the overall process are not shown). (1) Proton-promoted (proton pump, cation-anion antiport, organic anion efflux, dissociation of organic acids) and ligand-promoted (e.g. organic adds) dissolution of metal minerals. (2) Release of anionic (e.g. phosphate) nutrients and metal cations. (3) Nutrient uptake. (4) Intra- and extracellular sequestration of toxic metals biosorption, transport, compartmentation, predpitation etc. (5) Immobilization of metals as oxalates. (6) Binding of soluble metal species to soil constituents, e.g. clay minerals, metal oxides, humic substances.

Vlodavsky, I., Bar-Shavit, R., Ishai-Michaeli, R., Bashkin, R and Fuks, Z. (1991). Extracellular sequestration and release of fibroblast growth factor a regulatory mechanism Trends Biochem. Sci. 16, 268-271. 

Extracellular sequestration, often by extracellular polysaccharides on the cell... 

DCCD and vanadate. This indicates an active process energised by ATP. Ferrozine inhibition of Fe2+ and Fe3+ uptake implied the concerted involvement of both a Fe3+ reductase and FeoB in the uptake of iron supplied as Fe3+. It is concluded that FeoB-mediated Fe2+ represents a major pathway for H. pylori iron sequestration [189], In addition, growth experiments on the human pathogen L. pneumophila using artificial media, as well as replication studies within iron-depleted Hartmannella vermiformis amoebae and human U937 cell macrophages, provided evidence that the FeoB transporter is important for extracellular growth and intracellular infectivity [190],... 

Like most quaternary ammonium compounds, 2-PAM is distributed mainly to extracellular water, and some tissue sequestration occurs.100 2-PAM is only weakly bound to plasma proteins.100... 

In general, Zn homeostasis is maintained by three families of proteins (a) met-allothioneins (MT) that quickly bind, sequester, and hold Zn after influx into the cytoplasm, (b) Zrt-Irt-like (ZIP) proteins that likely mediate Zn influx into the cell, and (c) zinc transporter (ZnT) proteins that mediate efflux of cytoplasmic Zn to the extracellular space or sequestration in intracellular organelles. 

Studies on skeletal muscle also support an intracellular site of action of the MDIs. Thus, pr-MDI (10 4m) significantly blocked caffeine-induced contractures of the rat diaphragm both in presence and in absence of extracellular calcium (33). Such caffeine-induced contractures are believed to be mediated by intracellular calcium mobilized from the sarcoplasmic reticulum or other intracellular calcium pool (34). Furthermore, bu-MDI (10 M) depresses activation heat in the frog sartorius muscle upon stimulation (35), indicating a reduction in the quantity of calcium released from the sarcoplasmic reticulum, since activation heat represents the energy liberated in association with calcium mobilization and sequestration in contracting muscle (36,... 

The actual process of infection is not as simple as is usually believed. Most of the serotypes share a common receptor on host cells, which is an intercellular adhesion protein called ICAM-1. This is a transmembrane glycoprotein whose extracellular portion comprises several immunoglobulin domains of the IgG class. It appears that the normal role of ICAM-1 is to allow adhesion between the cell and leucocytes during injury or infection. Unwittingly, the ICAM-1 receptor has been hijacked by rhinoviruses as their receptor. Interestingly, ICAM-1 has other functions, which include sequestration of erythrocytes that have been infected by the malaria parasite Plasmodium falciparum, thus allowing them to avoid the attentions of the host s immune system. 

Olakanmi O, McGowan SE, Hayek MB, Britigan BE. Iron sequestration by macrophages decreases the potential for extracellular hydroxyl radical formation. J Clin Invest 1993 91 889-899. 

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