Membranes, biological calcium role

The previous paragraph stated the most obvious structural role of calcium. However Ca2+, like several other ions, for example Zn2+ and K+, is also important in stabilizing a range of less rigid biological structures, such as membranes, and determining and maintaining the secondary, tertiary, and quaternary structures... 

Phosphorus is one of the inorganic macronutrients in all known forms of life. Inorganic phosphorus in the form of phosphate (PO/ ) plays a major role in vital biological molecules, such as DNA and RNA. Living cells also utilize phosphate to transport cellular energy via adenosine triphosphate (ATP). Phospholipids are the main structural components of all cellular membranes. Calcium phosphate salts are... 

Complexes of alkali metals and alkaline-earth metals with carbohydrates have been reviewed in this Series,134 and the interaction of alkaline-earth metals with maltose has been described.135 Standard procedures for the preparation of adducts of D-glucose and maltose with the hydroxides of barium, calcium, and strontium have been established. The medium most suitable for the preparation of the adduct was found to be 80% methanol. It is of interest that the composition of the adducts, from D-glucose, maltose, sucrose, and a,a-trehalose was the same, namely, 1 1, in all cases. The value of such complex-forming reactions in the recovery of metals from industrial wastes has been recognized. Metal hydroxide-sugar complexes may also play an important biological role in the transport of metal hydroxides across cell membranes. 

IP3 is classified now as a second messenger with considerable influence on calcium movement from intracellular stores in a cell. Furthermore, diglycerides have a considerable and important effect on protein kinase C activity and location (Nishizuka, 1992). This is a classic example of an inactive (precursor) molecule being converted to a biologically active product. This reaction is an excellent example of the role of phospholipids in membrane processes through an enzyme-catalyzed reaction. 

With modest increase in intracellular ROS levels, activation of NF-kB takes place, which protects the cell against oxidative stress [45], Direct root of ROS participation in signal transduction from cell membrane to intracellular metabolic reactions were recently described. Among them - activation of potential-dependent K-channels and variation of membrane potential, inhibition of cellular protein phosphatases and restriction of activity of MAP-kinase [49]. Such view on intracellular role of ROS consider them as second messengers, which together with cyclic nucleotides, calcium ions, and other biologically active compounds provides adequate cell response to the outer signals. 

The morphological classification adopted in an earlier section (see pp. 89— 91) emphasizes the important role of membrane systems in calcification. Membranes, both in intracellular and extracellular calcification, are thought to be involved in an active transport of calcium to the site of calcification. They may also be involved in facilitating the availability of bicarbonate ions and in removing protons released during calcification. Thus, all the main ion species involved in biological calcification may be controlled by membrane processes. The ions are related according to the empirical equation... 

Within cells, including nerve cells, fluxes of Ca ions play an important role in signal transduction (Chapter 11). Most eukaryotic cells export calcium across the plasma membrane or deposit it in membrane-enclosed storage sites in order to maintain free cytosolic Ca levels at 100—200 nM, roughly 10,000 times less than in the extracellular space. This allows calcium to function as a second messenger and also as a carrier of biological... 

To begin, it is essential to note that the calcium cation is now recognized [63] as crucial to the functioning of biological processes. The role of calcium in membrane structure can be the following. Because... 

In keeping with their proposed cytoskeletal nature, IFPs initially were thought to serve a purely structural role in muscle cells. It was hypothesized that the function of these proteins was to keep other cytoplasmic proteins in proper relationship to one another, as well as to anchor the cytoplasmic contractile apparatus to the cell membrane. Flowever, subsequent developments in cell biology cast considerable doubt on this premise." The intermediate filaments are now known to serve a nucleic acid-binding function moreover, they are susceptible to processing by calcium-activated proteases and are substrates for cyclic adenosine monophosphate-dependent protein kinases. Thus, it has been proposed that all IFPs serve as modulators between extracellular influences governing calcium flux into the cell (and subsequent protease activation) and nuclear function at a transcriptional... 

The T-type or low-voltage-activated calcium channels have been identified in a variety of smooth muscle cells. They activate at low membrane potentials (around -50 mV) with a maximum around -20 mV, have a small conductance (7-8 pS with 110 mM Ba2+ as charge carrier), inactivate rapidly, and are blocked by 10-100 xM Ni2+ and a variety of compounds, including some of the organic calcium channel blockers. The biological role of the T-type channels remains to be established owing to the lack of specific blockers. 

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