Phosphorus metabolic role

Inorganic pyrophosphatase [EC 3.6.1.1] plays a central role in phosphorus metabolism by catalyzing the hydrolysis of the phosphoanhydride bond of inorganic pyrophosphate (or, diphosphate PPi). This cleavage reaction acts in conjunction with pyrophosphate-forming ligases to provide an additional thermodynamic impetus for certain biosynthetic reactions. For example ... 

Vitamin D3 is transported to liver where it undergoes a hydroxylation at C-25 into 1a,25-dihydroxyvitamin D3 (calcitriol) (Fig. 64). In the kidney, it undergoes further hydroxylations at different sites, depending on the serum Ca + concentration. The most biologically active metabolite of vitamin D3 is calcitriol, which plays important roles in the regulation of calcium and phosphorus metabolism. It is used for treating bone diseases, but is also involved in the cell proliferation and the inducement of cell differentiation [151]. 

However, despite the outstanding achievements of evolutionary biochemistry, many problems still await solution. Among these unsolved and relatively little-investigated problems of evolutionary biochemistry, there are the role of phosphorus compounds in chemical evolution, which preceded the appearance of life on Earth, and the evolution of phosphorus metabolism from primitive organisms to contemporary living creatures. 

I. S. Kulaev (1971). The role of inorganic polyphosphates in evolution of phosphorus metabolism. In R. Buvet and C. Ponnemperuma (Eds), Molecular Evolution, Vol. 1, North-Holland, Amsterdam, The Netherlands, p. 458. 

I. S. Kulaev and K. G. Skryabin (1971). Reactions of abiogenic transphosphorylation involving high-polymer polyphosphates and their role in the phosphorus metabolism evolution. In Abstracts of the Symposium on Origin of Life and Evolutionary Biochemisty, Varna, Bulgaria, p. 22. 

Cholesterol is also the precursor of vitamin D, which plays an essential role in the control of calcium and phosphorus metabolism. 7-Dehydrocholesterol (provitamin D is photolyzed by the ultraviolet light of sunlight to previtamin D, ... 

Magnesium ions. arc known to play a pan in the metabolic role of. A I P, and the upi>cr six spectra in Pia-ure 19-31 suggest that complex formation between the anionic phosphorus and the cation lakes place to cause the phosphorus chemical shifts to move downiield as the magnesium ion concentration is increased. 

The several forms of vitamin D play a major role in the regulation of calcium and phosphorus metabolism. One of the most important of these compounds, vitamin D3 (cholecalciferol), is formed from cholesterol by the action of ultraviolet radiation from the Sun. Vitamin Dg is further processed in the body to form hydroxylated derivatives, which are the metabolically active form of this vitamin (Figure 8.30). The presence of vitamin Dg leads to increased synthesis of a Ga -binding protein, which increases the absorption of dietary calcium in the intestines. This process results in calcium uptake by the bones. 

Vitamin A plays a crucial role in vision. Vitamin D is necessary for bone integrity because of its role in calcium and phosphorus metabolism. Vitamin E is an important antioxidant, and vitamin K plays a role in blood clotting. 

Duff, S.M.C., Sarath, C. and Plaxton, W.C. (1 994)The role of acid phosphatases in plant phosphorus metabolism. Physiologia Plantarum 90, 791-800. 

Vitamin D is a fat-soluble vitamin that has a major role in regulating calcium and phosphorus metabolism and is needed for calcium absorption from the intestines. 

Plants utilize molybdenum in minute amounts. The presence of one part per billion may eliminate molybdenum deficiency in plants. Evidence indicates that molybdenum plays a role in both nitrogen and phosphorus metabolism. Deficiency symptoms include an interveinal mottling with the leaf margins becoming brown. The leaf tissues wither leaving only the midrib and a few pieces of leaf blade and resulting in a characteristic appearance called whip tail (68). 

This vitamin plays a major role in the regulation of calcium and phosphorus metabolism. 

Until 1950, 13 mineral elements were classified as essential these comprised the major elements (calcium, phosphorus, potassium, sodium, chlorine, sulphur, magnesium) and the micro or trace elements (iron, iodine, copper, manganese, zinc and cobalt). By 1970, molybdenum, selenium, chromium and fluorine had been added to the list subsequently, arsenic, boron, lead, lithium, nickel, silicon, tin, vanadium, rubidium and aluminium have also been included, the list varying slightly according to the different authorities. Plant and animal tissues contain a further 30 mineral elements, in small quantities, for which no essential function has been found. They may be acquired from the environment, but it has been suggested that as many as 40 or more elements may have metabolic roles in mammalian tissues. Fortunately, many of these trace elements, especially those of more recent discovery, are required in such minute quantities, or are so widely distributed in foods for animals, that deficiencies are likely to be extremely rare under normal practical conditions. 

Phosphorus has more known fimctions than any other mineral element in the animal body. The close association of phosphorus with calcium in bone has already been mentioned. In addition, phosphorus occms in phosphoproteins, nucleic acids and phosphohpids.The element plays a vital role in energy metabolism in the formation of sugar-phosphates and adenosine di- and triphosphates (see Chapter 9). The importance of vitamin D in calcimn and phosphorus metabolism has already been discussed in Chapter 5. The phosphorus content of the animal body is considerably less than that of calcimn content. Whereas 99 per cent of the calcium found in the body occurs in the bones and teeth, the proportion of the phosphorus in these structures is about 80-85 per cent of the total the remainder is in the soft tissues and fluids, where it serves the essential fimctions mentioned above. The control of phosphorus metabolism is different from that of calcium. If it is in an available form, phosphorus is absorbed well even when there is an excess over requirement. The excess is excreted via the kidney or the gut (via sahva). In monogastric animals, the kidney is the primary route of excretion. Plasma phosphorus diffuses into saliva and in ruminants the large amount of chewing during rumination results in saliva being the major input of phosphorus into the rumen rather than the food. 

Vitamin D is the name for a structurally related set of molecules that play a major role in the regulation of calcium and phosphorus metabolism. Vitamin Dj is synthesized in the skin of mammals by the action of ultraviolet radiation on 7- dehydrocholesterol. 

Dihydroxycholecalciferol is able to act on a number of tissues with columnar epithelial cells, including intestinal mucosa, kidney tubules, the shell gland of birds and probably also various types of bone cell where it may assist the synthesis of osteocalcin (page 161). Its mode of action is very similar to that of steroid hormones (Figure 30.1). In this respect its precursor, vitamin Dj, may be considered to function as a prohormone rather than a vitamin. The ability of 1,25-DHCC and other metabolites of vitamin D3 to act on bone and kidney cells, as well as those of the intestine, means that vitamin D plays a key role in calcium and phosphorus metabolism (Hgure 30.2). 

Bloch, K., Snoke, J. E. and Yarnari, S. (1952) The role of phosphate in amino acid and protein metabolism. In Phosphorus Metabolism (W. D. McElroy and B. Glass, eds.) Vol. II, p. 82, Johns-Hopkins Press, Baltimore, Md. 

The importance of vitamin D—the sunshine vitamin—in human nutrition lies in the role of regulating calcium and phosphorus metabolism. Vitamin D promotes intestinal absorption of calcium and phosphorus and influences the process of bone mineralization. In the absence of vitamin D, mineralization of bone matrix is impaired, resulting in rickets in children and osteomalacia in adults. Although rickets is rare in the United States, it is still prevalent in many countries. 

W. C. Plaxton, Metabolic aspects of phosphate starvation in plants. Phosphorus in Plant Biology Regulatory Roles in Molecular, Cellular, Organi.smic, and Eco.sy.s-lein Proces.ses (J. P. Lynch and J. Deikman eds.), American Society of Plant Physiologists, 1998, p. 229. 

Factors that can predispose patients to developing metabolic bone disease include deficiencies of phosphorus, calcium, and vitamin D vitamin D and/or aluminum toxicity amino acids and hypertonic dextrose infusions chronic metabolic acidosis corticosteroid therapy and lack of mobility.35,39 Calcium deficiency (due to decreased intake or increased urinary excretion) is one of the major causes of metabolic bone disease in patients receiving PN. Provide adequate calcium and phosphate with PN to improve bone mineralization and help to prevent metabolic bone disease. Administration of amino acids and chronic metabolic acidosis also appear to play an important role. Provide adequate amounts of acetate in PN admixtures to maintain acid-base balance. 

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