Amino acid absorption

Several changes which can adversely influence the nutritional quality occur in proteins that are subjected to severe alkaline treatments. Losses in the amino acids (lysine and cystine, particularly), drops in digestibility, and reduction in net protein utilization all increase as the severity of the alkaline treatment increases ( ). Increases in either temperature or pH of treatment caused similar results. Decreased intestinal absorption amino acids was attributed to LAL-like cross-links and racemization. Kraus and Schmidt (68) also observed a reduction in digestibility of milk proteins as treatment temperature increased from 30 to 90°C at pH 12. 

Parathyroid hormone, a polypeptide of 83 amino acid residues, mol wt 9500, is produced by the parathyroid glands. Release of PTH is activated by a decrease of blood Ca " to below normal levels. PTH increases blood Ca " concentration by increasing resorption of bone, renal reabsorption of calcium, and absorption of calcium from the intestine. A cAMP mechanism is also involved in the action of PTH. Parathyroid hormone induces formation of 1-hydroxylase in the kidney, requited in formation of the active metabolite of vitamin D (see Vitamins, vitamin d). 

Colorimetric and Fluorimetric Analysis. The functional groups of amino acids exhibit Htde absorption of uv light from 210 to 340 nm where uv absorption spectrometry is most conveniently conducted. Thus color or fluorescence formation reactions are employed for amino acid detection (128). 

Proteins and Meals. Nutritional properties of the oilseed protein meals and their derived products are deterrnined by the amino acid compositions, content of biologically active proteins, and various nonprotein constituents found in the defatted meals. Phytic acid (3), present as salts in all four meals, is beheved to interfere with dietary absorption of minerals such as 2inc, calcium, and iron (67) (see Food toxicants, naturally occurring Mineral nutrients). ... 

FIGURE 4.15 The ultraviolet absorption spectra of the aromatic amino acids at pH 6. 

Reagents which form a derivative that strongly absorbs UV/visible radiation are called chromatags an example is the reagent ninhydrin, commonly used to obtain derivatives of amino acids which show absorption at about 570 nm. Derivatisation for fluorescence detectors is based on the reaction of non-fluorescent reagent molecules (fluorotags) with solutes to form fluorescent... 

According to Charbonneau et al. (1985), aequorin is a single chain peptide consisting of 189 amino acid residues, with an unblocked amino terminal. The molecule contains three cysteine residues and three EF-hand Ca2+-binding domains. The absorption spectra of aequorin and BFP are shown in Fig. 4.1.3, together with the luminescence spectrum of aequorin and the fluorescence spectrum of BFP. 

Amino acids promote the production of proteins, enhance tissue repair and wound healing, and reduce the rate of protein breakdown. Amino acids are used in certain disease states, such as severe kidney and liver disease, as well as in TPN solutions. (See the last section of this chapter for a more detailed discussion of TPN.) TPN may be used in patients with conditions such as impairment of gastrointestinal absorption of protein, in patients with an increased requirement for protein, as seen in those with extensive bums or infections, and in patients with no available oral route for nutritional intake ... 

FIGURE 3 The infrared spectrum of an amino acid, with the groups contributing to some ol the peaks identified. Notice that the spectrum displays the intensity of absorption. 

With a fixed amino acid concentration of 0.02 M, the rate constant proved independent of the concentration of BrO" over the range (0.38-3.09) x 10"3M for N-Br-aminoisobutyric acid and N-Br-Proline. The plot of the obtained initial absorbance values against the initial N-Br-amino acid cone tration shows that Beer s law is obeyed, and the values for the molar absorptivity of the studied N-bromoamino acids are listed in Table 2. 

Under normal feeding patterns the rate of tissue protein catabolism is more or less constant throughout the day it is only in cachexia that there is an increased rate of protein catabolism. There is net protein catabolism in the postabsorptive phase of the feeding cycle and net protein synthesis in the absorptive phase, when the rate of synthesis increases by about 20-25%. The increased rate of protein synthesis is, again, a response to insulin action. Protein synthesis is an energy-expensive process, accounting for up to almost 20% of energy expenditure in the fed state, when there is an ample supply of amino acids from the diet, but under 9% in the starved state. 

Mercer LP, Dodds SJ, Smith Dl Dispensable, indispensable, and conditionally indispensable amino acid ratios in the diet. In Absorption and Utilization of Amino Acids. Friedman M (editor). CRC Press, 1989. 

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. 

Distribution. Once inside the body, trichloroethylene is easily absorbed into and distributed through the circulatory system. The amount that is not absorbed initially on inhalation is expired unchanged (see Section 2.3.1.1). Absorption from the gastrointestinal tract often leads to a first pass through the liver, where toxic metabolites can form (see Section 2.3.3). Trichloroethylene and its metabolites may form adducts with blood proteins, and the metabolite glyoxylate may become incorporated into amino acids (Stevens et al. 1992), thus facilitating their distribution. The ability of these compounds to traverse membranes accounts for then-generalized systemic effects. 

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