Amino dispensable

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. 

Two amino acids—cysteine and tyrosine—can be synthesized in the body, but only from essential amino acid ptecutsots (cysteine from methionine and tyrosine from phenylalanine). The dietary intakes of cysteine and tytosine thus affect the requirements for methionine and phenylalanine. The remaining 11 amino acids in proteins are considered to be nonessential or dispensable, since they can be synthesized as long as there is enough total protein in the diet—ie, if one of these amino acids is omitted from the diet, nitrogen balance can stiU be maintained. Howevet, only three amino acids—alanine, aspartate, and glutamate—can be considered to be truly dispensable they ate synthesized from common metabolic intetmediates (pyruvate, ox-... 

P. J. Reeds, Dispensable and Indispensable Amino Acids for humans. http //jn.nutrition.org J. Nutr. 2000, 130 (7), 1835S-1840S. PMID 10867060 http //www.ncbi.nlm..nih.gov (accessed 2 April 2008). 

The PNA chain was linked to the peptide spacer glutamic acid-(y-tert-butyl ester)-(fi-aminohexanoic acid)-(fi-aminohexanoic acid) (Glu [OtBuj-fiAhx-fiAhx) via an enzymatically cleavable Glu-Lys handle. The Glu [OtBuj-fiAhx-fiAhx spacer was coupled to the amino-functionalized membrane by standard Fmoc-Chemistry. Then the membranes were mounted in an ASP 222 Automated SPOT Robot and a grid of the desired format was dispensed at each position. The free amino groups outside the spotted areas were capped and further chain elongation was performed with Fmoc-protected PNA monomers to synthesize the desired PNA oligomers (18). After completion of the synthesis, the PNA oligomers were cleaved from the solid support by incubation with bovine trypsin solution in ammonium bicarbonate at 37 °C for 3 h. 

Essential and non-essential (indispensable and dispensable) amino acids... 

An interesting possibihty, never investigated, is that the bear possesses the ability to synthesise both dispensable and non-dispensable amino acids de novo, from the ammonia released by the microorganisms. As far as is known, no mammal possesses the enzymes necessary to synthesise the indispensable amino acids. It would be interesting if another adaptation to such a long hibernation is development of enzymes necessary to synthesise indispensable amino acids. This possibility is supported by the... 

Milk is a remarkably complex biological fliud. It contains several hundred different molecules including enzymes and also different cells, e.g. inunune cells. In particular, it contains proteins, fat, lactose, both the indispensable and dispensable amino acids, essential fatty acids, micronutrients, cholesterol and phospholipids. Milk is essential for the first four months of life. The major protein in milk is... 

If the chemistry is amenable, it is possible to synthesize a large number of small samples of polymers by simply mixing the ingredients in either small vials or multiwell plates. For example, Brocchini et al. prepared a library of 112 polymers by mixing the monomers in individual vials which were placed in a water bath [22]. Akinc et al. synthesized a library of 24 unique poly(j3-amino esters) via the conjugate addition of acrylates and amines by mixing the monomers in sample vials fitted with stir bars [23]. To speed up this process, a liquid handling robot can be used to dispense the raw materials into an array of vials [24]. 

Later work by the Bresow group dispensed with metals entirely. Disubstitution of 3-cyclodextrin with imidazole groups, analogous to the histidine side chains of amino acids in ribonuclease A, led to a catalyst that increases the rate of a small cyclic phosphate by a factor of 120. The selectivity for one product over the other was 99 1 but the rate increase and selectivity were only observed for cyclodextrins... 

The high add and moisture sensitivity of silyiamines has been a major obstacle to their use in amino group protection. Primary amines have been protected as their terf-butyldiphenylsilyl derivatives whose steric bulk militates against further reaction to form an ty,/V-disilylamine.4S0 fm-Butyldiphenylsilylamines have remarkable stability towards strongly basic conditions (e.g., 20% potassium hydroxide in refluxing methanol), but they cannot even withstand brief expo-sure to 80% acetic acid at room temperature. If silyiamines are used at all in synthesis, they are usually prepared under anhydrous conditions, and used for one or two steps before their flimsy services are dispensed with. 

A peptide library can be synthesized using the SPOT synthesis technique to form a low-density peptide spot array (e.g., 25 spots/cm ). In this method, different peptides are synthesized in situ as low-density arrays on cellulose membrane or paper (8). The volume of Fmoc-amino acids and coupling reagents dispensed creates a specific SPOT size that determines both the scale of reaction and the absolute number of peptides that can be arranged on an area of a membrane. Cotton (another form of cellulose) and polystyrene-grafted polyethylene film segments also have been used as solid supports. Recently, polymeric membranes that are chemically, mechanically, and thermally more stable have been developed, which include hydroxy-functionalized PEG acrylate polypropylene membranes and an amino-functionalized ester-free PEG... 

The amino acid module performs the dissolution, activation, and delivery of amino adds to the synthesis cabinet. This is accomplished via a robotic arm with a probe attachment. Liquids can be dispensed or withdrawn from amino acid vials through the probe. In addition, nitrogen can be bubbled to aid in the dissolution of the amino acid. After each amino acid coupling the probe is thoroughly washed, both internally and externally, to eliminate cross contamination. The amino acid module can hold up to 72 anoino acids in three 24-position racks. A rack can be assigned to each colunm or all 72 can be used for single column synthesis. 

IFN (3-Ib (Betaseron) is a purified protein produced by recombinant DNA technology with 165 amino acids and approximate molecular weight of 18,500 daltons. Lyphylized vials contain 0.3 mg IFN(3-lb with mannitol (15 mg) and albumin (15 mg) as stabilizers. Reconstitution with the diluent supplied produces a 0.54% sodium chloride solution. IFN (3-lb or Betaseron is also dispensed in a pre-filled syringe at a dose of 22 ig (6MIU) per dose for 66j.tg/week. A higher dose of 44 j.Lg (12 MIU) per dose for 132 j.tg per week is also available. The recommended dosing schedule is three times a week as a subcutaneous injection. 

Serine, glycine, and cysteine are dispensable (or nonessential) amino acids because they can be biosynthesized from precursors that are readily available in the body Serine can be made from or converted back to glucose, and also is used in the synthesis of cysteine. The pathways for these conversions are detailed in Chapter 8. 

Tyrosine and tryptophan, as well as phenylalanine, are the aromatic amino acids. The body can convert phenylalanine to tyrosine. Thus, tyrosine is a dispensable (nonessential) amino acid. 

In Table 1.5 the classical amino acids are segregated according to their necessity in the diet, Those that are required to maintain life are called indispensabJe (essenfioJ) amino acids. Those that may be present in the diet but can be omitted without threatening life are called dispensable (norte5sc dw0 amino acids. The proteins of the most value, from a nutritional point of view, are the ones that contain all the indispensable amino acids as well as a variety of dispensable amino acids. 

Extra attention was devoted to proteins and en7ymes, as they have been the traditional "bread and butter" of the nutritional biochemist. The amino acids that form proteins can be classified in several ways (1) relatively hydrophilic or lipophilic, (2) dispensable or indispensable (noncssentiai or essential), (3) glycogenic or ketogenic, and, hnally, (4) classical or modified. Only a minority of the amino acids in proteins are modified after incorporation into the polypeptide chain. 

Biosynthesis of Dispensable Amino Acids Clucogt icand Ketogcnic Amino Adds... 

---