Calcium ions mammals

Calcium is a macronutrient essential for all organisms. Chlorine is a micronutrient essential for higher (ie, seed) plants but not considered essential for mammals. Above certain levels chloride is toxic to plants and animals, thus when considering calcium chloride, potentially large concentrations of calcium ion can be tolerated, but at these concentrations the chloride ion becomes toxic. 

Mammals synthesize phosphatidylserine (PS) in a calcium ion-dependent reaction involving aminoalcohol exchange (Figure 25.21). The enzyme catalyzing this reaction is associated with the endoplasmic reticulum and will accept phosphatidylethanolamine (PE) and other phospholipid substrates. A mitochondrial PS decarboxylase can subsequently convert PS to PE. No other pathway converting serine to ethanolamine has been found. 

To understand the inhibition of a-amylase by peptide inhibitors it is crucial to first understand the native substrate-enzyme interaction. The active site and the reaction mechanism of a-amylases have been identified from several X-ray structures of human and pig pancreatic amylases in complex with carbohydrate-based inhibitors. The structural aspects of proteinaceous a-amylase inhibition have been reviewed by Payan. The sequence, architecture, and structure of a-amylases from mammals and insects are fairly homologous and mechanistic insights from mammalian enzymes can be used to elucidate inhibitor function with respect to insect enzymes. The architecture of a-amylases comprises three domains. Domain A contains the residues responsible for catalytic activity. It complexes a calcium ion, which is essential to maintain the active structure of the enzyme and the presence of a chloride ion close to the active site is required for activation. 

Calcium. Calcium, ihe most abundant mineral element in mammals, comprises 1.5-2.0 w1 G of Ihe adult human body, over 99 wt (i of which is present in bones nnd teeth. About 48 of scrum calcium is ionic, ca 46G is bound nr hlood proteins, the rest is present as diffusible complexes, e.g.. of citrate. The calcium ion level must he maintained within definite limits... 

Vitamin K in birds and mammals occurs in the reduced form (as a hydroquinone) and acts as an essential factor for the carboxylation of certain proteins (transformation of bound glutamic acid into y-carboxyglutamic acid). Carboxyglutamic acid residues impart important properties to the relevant proteins, such as the ability to bind calcium ions and phospholipids, which are necessary for their activation and for them to function in blood clotting. The best... 

The concentration of calcium in the hlood plasma of most mammals and many vertebrates is quite constant al about 2.5 niM 110 milligrams pet 100 milliliters plasma). In the plasma, calcium exists in three forms ill as the tree ion. 12) bound to proteins, and t.l) complexed with organic te.g., citrate) or inorganic ie,g., phnsphatei acids. The tree ion accounts lor about 47.5% of the plasma calcium 46% is bound lo proteins and 6.5% is in complexed form. Of the latter, phosphate and citrate account for half. 

Net bone growth In mammals subsides just after puberty, but a finely balanced, highly dynamic process of disassembly (resorption) and reassembly (bone formation), called remodeling, goes on throughout adulthood. Remodeling permits the repair of damaged bones and can release calcium, phosphate, and other Ions from mineralized bone Into the blood for use elsewhere In the body. 

In mammals, both a thyroid and a parathyroid hormone exist to regulate the level of circulating calcium. Concentrations of calcium, inside and outside of cells are about 10 and 10 M respectively. Release of calcium, whether from outside the cell or from internal stores, can trigger a wide range of biol( ical responses. These concentration levels are controlled by the plasma membrane, membranes of the endoplasmic reticulum (in muscle the sarcoplasmic reticulum), and the inner membrane of mitochondria. One important function of calcium is to control the permeability of semi-permeable membranes which maintain their integrity in its presence and become porous and leaky in its absence. This control follows from the abundance of this ion, its divalent character, and the presence of phosphate anions in the membranes (Ames, Tsukada and Nesbett, 1967). 

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