Metabolic function

Metabolic Functions. Bones act as a reservoir of certain ions, in particular Ca " and which readily exchange between bones and blood. 

Metabolic Functions. The formation of phosphate esters is the essential initial process in carbohydrate metaboHsm (see Carbohydrates). The glycolytic, ie, anaerobic or Embden-Meyerhof pathway comprises a series of nine such esters. The phosphogluconate pathway, starting with glucose, comprises a succession of 12 phosphate esters. 

Metabolic Functions. Zinc is essential for the function of many enzymes, either in the active site, ie, as a nondialyzable component, of numerous metahoenzymes or as a dialyzable activator in various other enzyme systems (91,92). WeU-characterized zinc metahoenzymes are the carboxypeptidases A and B, thermolysin, neutral protease, leucine amino peptidase, carbonic anhydrase, alkaline phosphatase, aldolase (yeast), alcohol... 

Metabolic Functions. The functions of the thyroid hormones and thus of iodine are control of energy transductions (121). These hormones increase oxygen consumption and basal metaboHc rate by accelerating reactions in nearly all cells of the body. A part of this effect is attributed to increase in activity of many enzymes. Additionally, protein synthesis is affected by the thyroid hormones (121,122). 

Metabolic Functions. Manganese is essential for normal body stmcture, reproduction, normal functioning of the central nervous system, and activation of numerous enzymes (126). Synthesis of the mucopolysaccharide chondroitin sulfate involves a series of reactions where manganese is required in at least five steps (127). These reactions are responsible for formation of polysaccharides and linkage between the polysaccharide and proteins that form... 

Metabolic Functions. Chromium (ITT) potentiates the action of insulin and may be considered a cofactor for insulin (137,138). In in vitro tests of epididymal fat tissue of chromium-deficient rats, Cr(III) increases the uptake of glucose only in the presence of insulin (137). The interaction of Cr(III) and insulin also is demonstrated by experimental results indicating an effect of Cr(III) in translocation of sugars into ceUs at the first step of sugar metaboHsm. Chromium is thought to form a complex with insulin and insulin receptors (136). 

METALLOPROTEINS. Metalloproteins are either metal storage forms, as in the case of ferritin, or enzymes in which the metal atom participates in a catalyti-cally important manner. We encounter many examples throughout this book of the vital metabolic functions served by metalloenzymes. 

Human labor dominated all subsistence foraging activities, as the food acquired by gathering and hunting sufficed merely to maintain the essential metabolic functions and to support veiy slow population growth. Societies not very different from this ancestral archetype survived in some parts of the world (South Africa, Australia) well into the twentieth century Because they commanded veiy little energy beyond their subsistence food needs, they had very few material possessions and no permanent abodes. 

Information concerning the metabolic function of unusual naturally occurring plant constituents might be used to develop new growth regulators. An example of a development that arose in this way began with the observation by Tolbert (143) that as much as 30% of the total soluble phosphorus in plant roots, and sometimes in the leaves,... 

A specific role for vitamin E in a required metabolic function has not been found. In addition to its direct antioxidant effects, a-tocopherol has been reported to have specific molecular functions. 

The antimetabolites interfere with various metabolic functions of cells, thereby disrupting normal cell functions. They inactivate enzymes or alter the structure of DNA, changing the DNA s ability to replicate These drag are most effective in the treatment of rapidly dividing neoplastic cells. Examples of the antimetabolites include methotrexate and fluorouracil (Adrucil). 

On the other hand, organisms can also produce chelating agents to acquire metals that are necessary for certain metabolic functions. These chelating agents are often extremely specific for a given metal and are used to "collect" metals from solution or maintain a desired concentration of metals inside the cell. 

Cells exposed to excessive levels of salinity have to acquire essential nutrients from a milieu with a preponderance of ions that are potentially toxic and non-essential. In this ionic environment the success of a plant cell will require intracellular tolerance and/or specific acquisition of nutrients essential for normal metabolic functioning. The cell is also exposed to an unfavourable water balance with an absolute requirement to maintain an internal osmotic regulation that favours uptake of water into the cell (Stavarek Rains, 1984 ). 

The classification of P450s, which is based on amino acid sequencing, bears some relationship to metabolic function. That said, some xenobiotic molecules, especially... 

Besides water, the diet must provide metabolic fuels (mainly carbohydrates and lipids), protein (for growth and turnover of tissue proteins), fiber (for roughage), minerals (elements with specific metabolic functions), and vitamins and essential fatty acids (organic compounds needed in small amounts for essential metabolic and physiologic functions). The polysaccharides, tri-acylglycerols, and proteins that make up the bulk of the diet must be hydrolyzed to their constituent monosaccharides, fatty acids, and amino acids, respectively, before absorption and utilization. Minerals and vitamins must be released from the complex matrix of food before they can be absorbed and utifized. 

Besides watet, the diet must provide metaboEc fuels (carbohydrate and fat) fot bodily growth and activity protein fot synthesis of tissue proteins fiber for roughage minerals for specific metabolic functions cettain polyunsamtated fatty acids of the n-3 and n-6 famihes fot eicosanoid synthesis and other functions and vitamins, otganic compounds needed in small amounts for many varied essential functions. 

THE VITAMINS ARE A DISPARATE GROUP OF COMPOUNDS WITH A VARIETY OF METABOLIC FUNCTIONS... 

VITAMIN E DOES NOT HAVE A PRECISELY DEFINED METABOLIC FUNCTION... 

Niacin was discovered as a nutrient during studies of pellagra. It is not strictly a vitamin since it can be synthesized in the body from the essential amino acid tryptophan. Two compounds, nicotinic acid and nicotinamide, have the biologic activity of niacin its metabolic function is as the nicotinamide ring of the coenzymes NAD and NADP in oxidation-reduction reactions (Figure 45-11). About 60 mg of tryptophan is equivalent to 1 mg of dietary niacin. The niacin content of foods is expressed as mg niacin equivalents = mg preformed niacin + 1/60 X mg tryptophan. Because most of the niacin in cereals is biologically unavailable, this is discounted. 

Consolazio, C. F. Johnson, R. E. and Pecora, L. J. Physiological Measurements of Metabolic Functions in Man, McGraw-Hill, New York 1963. 

Nitrite (or compounds at the same or lower oxidation level) is produced microbiologically from nitrate, and may then react with the substrate to produce stable end products. The production of nitrite is the sole metabolic function of the bacteria and, in view of concern over the presence of nitrate in groundwater, the following possible environmental significance of these or analogous reactions should not be overlooked ... 

In all the examples, organisms with undefined metabolic functions were present and probably fulfilled an important role in providing complex organic substrates in the form of cell lysis products or nutritional requirements. 

Hareland WA, RL Crawford, PJ Chapman, S Dagley (1975) Metabolic function and properties of 4-hydroxy-phenylacetic acid 1-hydrolase from Pseudomonas acidovorans. J Bacteriol 121 272-285. 

Most of the physiologic activity of thyroid hormones is from the actions of T3. T4 can be thought of primarily as a prohormone. Eighty percent of needed T3 is derived from the conversion of T4 to T3 in peripheral tissue under the influence of tissue deiodinases. These deiodinases allow end organs to produce the amount of T3 needed to control local metabolic functions. These enzymes also catabolize T3 and T4 to biologically inactive metabolites. Thyroid hormones bind to intracellular receptors and regulate the transcription of various genes. 

The kidneys are located on the posterior part of the abdomen on either side of the spine, below the diaphragm, and behind the liver and stomach. They are bean-shaped and weigh approximately 150 grams (0.33 lb) each. The primary function of the kidneys is excretion. They work to excrete waste products through a series of steps involving glomerular filtration, secretion, and reabsorption. The kidneys also have several endocrine (e.g., production of erythropoietin and renin) and metabolic (e.g., vitamin D activation and drug metabolism) functions. 

Electrolytes, vitamins, and trace elements are essential for numerous biochemical and metabolic functions and should be added to PN daily unless otherwise not indicated. 

Cannabimimetics are also shown to affect reproductive and metabolic functions indirectly by hormonal modulation through the hypothalamic and pituitary regulatory centers. They are found to reduce serum levels of the luteinizing hormone, prolactin, growth hormone, and thyroid-stimulating hormone, and to increase corticotropin (Murphy, 1998). 

With these promoieties, the 3-phenolic hydroxy group of p-estradiol (the normally metabolized functional group) was blocked so that first-pass conjugative metabolism could be reduced. The relative bioavailability of estradiol was significantly improved when administered in these prodrug forms. A 17-fold increase was observed with the estradiol-3-salicylate. The P-estradiol-3-anthrani-late increased the systemic availability five-fold. 

The effect of the material on cellular metabolism is also an important measure of biocompatibility. To determine such effects, cultured ex vivo cells can be exposed to the polymer and the growth rates compared to controls [216,217], The metabolic function of the cells can be tested by assay for production of a marker enzyme. An additional advantage of this type of test is that it avoids the use of live animals. 

Blood/pulmonary agents, which interfere with metabolic functions such as hydrogen cyanide (AC) or phosgene (CG). 

The cells of the body require a continuous supply of oxygen to produce energy and carry out their metabolic functions. Furthermore, these aerobic metabolic processes produce carbon dioxide, which must be continuously eliminated. The primary functions of the respiratory system include ... 

---