Calcium structural 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... 

Calcium oxalate (723) occurs as the monohydrate (whewellite, the thermodynamically stable form under ambient conditions (724)), the dihydrate (weddellite) in plant calcium stores and in sap, or the trihydrate (725). Calcium oxalate also plays a structural role in plants. Oxalate, for example from excessive amounts of rhubarb or spinach, inhibits absorption of Ca2+ from the GIT precipitation of calcium oxalate is the reason for the toxicity of oxalates. Calcium oxalate may also occur in man, where it can appear as minute star-shaped crystals in the urine. It is the main constituent of the majority of urinary calculi in man (726,727). The relationships between dietary calcium... 

In addition to its structural role in bone, and in teeth, the calcium ion is a carrier of chemical messages. It influences secretion, contraction of muscle, cell division, growth, transcription, as well as other key physiological processes. 

The calcium ion is a key factor in human nutrition. It has an important structural role in bone and teeth and is a regulatory factor in many aspects of metabolism. 

Many proteins, including many enzymes, contain hghtly bound metal ions. These may be inhmately involved in enzyme catalysis or may serve a purely structural role. The most common tightly bound metal ions found in metalloproteins include copper (Cu+ and Cu +), zinc (Zn +), iron (Fe + and Fe +), and manganese (Mn +). Other proteins may contain weakly bound metal ions that generally serve as modulators of enzyme activity. These include sodium (Na+), potassium (K+), calcium (Ca +), and magnesium (Mg +). There are also exotic cases for which enzymes may depend on nickel, selenium, molybdenum, or silicon for activity. These account for the very small requirements for these metals in the human diet. 

The structural role of calcium in bones and teeth is well known, but many proteins owe their structural integrity to the presence of metal ions that tie together and make rigid certain portions of these large molecules, portions that would otherwise be only loosely linked. Metal ions particularly known to do this are Ca2+ and Zn2+. 

The calcium ion in a-LA plays a structural role in stabilizing the protein. The thermal stability of the calcium-bound form of a-LA increases more than 40 °C compared to that of the apo-form. At low pH (e.g. pH 2), a-LA releases the calcium ion and becomes partially unfolded (molten globule state). This partially unfolded protein loses its tertiary structure but retains its secondary structure. Other metals, such as manganese or magnesium, are able to compete with calcium at the same site with a similar stabilizing effect. However, the binding of zinc, which is proposed to bind at different locations, decreases a-LA stability. ... 

Calcium is the most abundant mineral in the human body. About 99% is in the bones and teeth where it plays a structural role and the remaining 1% is in the body tissues and fluids where it is essential for muscle contraction, nerve impulse transmission, and cell metabolism. 

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... 

In the case of the buffering proteins, calcium binding has little or no significant effect on the structure of the protein and the function of the protein is most likely limited to its calcium-binding role. The best studied example of the latter is calbindin D9k. 

Although calcium (Ca) metal was discovered in 1808 independently by Sir Humphry Davy and Berzelius and Pontin, the pure metal was first produced by Moissan in 1898. The name of calcium is derived from the Latin calx , meaning lime. Calcium constitutes 3.63% of the Earth s crust, and is the fifth most abundant element in the environment as well as in the human body. Due to its reactivity, it only occurs naturally in the form of its compounds for example, various magmatic rocks, carbonate (limestone), and sulfate. Calcium is indispensable for life, namely for the maintenance of structure and metabolism. Its structural roles include that of coral, the secreted shells of mollusks and, in particular, the internal skeleton of vertebrates (Hluchan and Pomerantz 2002). 

Elements such as sodium, potassium and chlorine have primarily an electrochemical or physiological function and are concerned with the maintenance of acid-base balance, membrane permeability and the osmotic control of water distribution within the body. Some elements have a structural role, for example calcium and phosphorus are essential components of the skeleton and sulphur is necessary for the synthesis of structural proteins. Finally, certain elements have a regulatory function in controlling cell replication and differentiation zinc acts in this way by influencing the transcription process, in which genetic information in the nucleotide sequence of DNA is transferred to that of an RNA molecule. It is not uncommon for an element to have a number of different roles for example, magnesium functions catalytically, electrochemically and structurally. 

Th is precise arrangement is seen binding zinc in very different proteins,... J. W. Torrance et al. Evolution of binding sites for zinc and calcium ions playing structural roles. 2008. Proteins 71(2), p. 813. 

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