Homeostatic regulation protein

A possible function of this intracellular sulfur cycle is to buffer, i.e. to homeostatically regulate, the cysteine concentration of the cells. Irrespective of whether sulfate, cysteine, or sulfur dioxide is available as sulfur source, the intracellular sulfur cycle would allow a plant cell to use as much of these compounds as necessary for growth and development. At the same time, it would give a plant cell the possibility to maintain the cysteine pool at an appropriate concentration by emitting excess sulfur into the atmosphere. Thus, emission of hydrogen sulfide may take place when the influx of sulfur in the form of sulfate, cysteine, or sulfur dioxide exceeds the conversion of these sulfur sources into protein, glutathione, methionine, and other sulfur-containing components of the cell. 

Element-specific detection by ICP-MS has been widely used in the characterization of metallothioneins (MTs). The biological importance of these proteins is due to their role in homeostatic regulation of essential heavy metals like Cu and Zn. On the other hand, MT protects the cells from harmful chemicals, like nonessential and excessive essential heavy metals, reactive oxygen species, radicals, and alkylating agents. Fararello et reviewed different chromatographic approaches with ICP-MS detection for the multielemental speciation in MTs and MT-like proteins. 

Fig. 1 Proposed homeostatic regulation of inflammation in effective host defence. The initial phase of inflammation is initiated by a host of pro-inflammatory cytokines and eicosanoids which subsequently become diminished with time, and are coupled with the likely activation of anti-inflammatory and pro-resolution mediators, including the lipoxins, resolvins and protectins. Typically, IL 13 up-regulates 15-LO gene expression of human blood monocytes for example (Nassar et al. 1994). The associated increase in enzyme activity results in an increase in LX generation which promotes the resolution phase of inflammation. IL, interleukin TNF-a, tumour necrosis factor-a MCP-1, monocyte chemotactic protein-1 RANTES, regulated upon activation, normal T-cell expressed and secreted TGF i, transforming growth factor...

The disorders of calcium homeostasis are related to the calcium content of the extracellular fluid, which contains less than 0.5% of the total body stores of calcium. Skeletal bone contains more than 99% of total body stores of calcium. ECF calcium is moderately bound to plasma proteins (46%), primarily albumin. Unbound or ionized calcium is the physiologically active form and is the fraction that is homeostatically regulated. Extracellular calcium, however, is most commonly measured as the total serum calcium level, which includes both bound and unbound calcium. The normal total calcium serum concentration range is 8.5 to 10.5 mg/dL. °... 

Sixliultt ion acts in concert with other electrolytes, in particular K. to regulate the osmotic pressure and to maintain the appropriate water and pi I balance ot the body. Homeostatic control of these functions is accomplished by the lungs and kidneys inlereciing by way of the blood. Sodium is essential for glucose absorption and transport of other substances across cell membranes. It is also involved, as is KJ. ill transmitting nerve impulses and in muscle relaxation. Potassium ion acts as a catalyst in the intracellular fluid, in energy metabolism, and is required for carbohydrate and protein metabolism. 

CaSR may also influence the proliferative and apoptotic status of the cells indirectly via modulation of cell volume homeostasis. Indeed, stimulation of CaSR in human epithelial cells induces upregulation of volume-regulated anion channels (VRAC) via a G protein-mediated increase in intracellular cAMP (Shimizu, et al., 2000). Proliferation and apoptosis are associated with essential volume perturbations [e.g., (Lang, et al., 2000)] and VRAC, a key component of homeostatic volume regulation, has been directly implicated in proliferation (Chen, et al., 2002, Doroshenko, et al., 2001, Shen, et al., 2000, Wang, et al., 2002) and apoptosis (Lemonnier, et al., 2004, Okada, et al., 2001, Okada, et al., 2006, Shen, et al., 2002). Consequently, extracellular Ca2+ may affect carcinogenesis via the CaSR-VRAC-cell volume links. The Ca2+ -permeable store-operated channel (SOC) is directly and functionally coupled to VRAC in an androgen-dependent LNCaP human prostate cancer epithelial cell line (Lemonnier, et al., 2002), evidence for another, CaSR-unrelated, potential mechanism for extracellular Ca2+ involvement in proliferative and apoptotic events. 

Hormones are secreted by specialized glands (adrenal, hypothalamus, ovary, pancreas, parathyroid, pineal, pituitary, testes, thyroid) or other tissues (e.g., heart, gut, and kidney), and regulate the cellular activities of distant tissues. Plasma levels of hormones are tightly regulated through homeostatic feedback systems. The peptide and protein hormones typically have short half-lives (minutes), which allow rapid changes in plasma levels and rapid enhancement or attenuation of their biological effects. 

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