Amino acids, isolation aromatic

Root exudates A wide variety of chemicals, such as sugars, amino acids, and aromatics, is excreted by roots of plants. Very little information is available on the allelopathic interaction of root exudates with the higher plants, except for the identification of a few products in isolated cases (46). 

A limited amount of information can be obtained by the use of proteolytic enzymes that detach either amino acids or dipeptides sequentially from the C-terminus. They are thus complementary to the aminopeptidases and dipeptidyl aminopeptidases. Two pancreatic enzymes, carboxypeptidases A and B, differ in specificity. The former preferentially liberates C-terminal amino acids with aromatic side chains, somewhat less readily amino acids with alkyl side chains and, more slowly still, other amino acids, but not Pro, Arg, Lys and His. In contrast, carboxypeptidase B releases only C-terminal Arg, Lys and His. Carboxypeptidase Y is much less specific and is capable of removing all amino acids, although Gly and Pro are liberated only slowly. As with aminopeptidases, it is advisable to analyse the hydrolysate at intervals in order to determine the C-terminal sequence of amino acids. An interesting recent development (Carles et al., 1988) uses carboxypeptidase to effect transpeptidation between the protein being sequenced and a tritiated amino acid. The labelled protein is then degraded by various specific methods and then the labelled fragments are isolated by gel electrophoresis and subjected to Edman degradation. 

Other groups also used gel filtration exchange to measure middle molecules and perform in vitro toxicity tests (C7, D21). However, many of the middle molecular weight substances isolated by these techniques proved to be much smaller than anticipated. This discrepancy was due to the intrinsic inadequacies of the standard gel filtration techniques for the isolation of middle molecules, as pointed out by Furst et al. (F13) and later by Schoots et al. (S13). These investigators used analytical techniques to demonstrate that middle molecular fractions obtained by gel filtration comprised many low-molecular-weight solutes, such as carbohydrates, amino acids, polyols, aromatic substances, and other UV-absorbing solutes, and also sodium chloride, acetate, phosphate, and sulfate (S10). Thus these fractions do not exclusively represent middle molecules. 

It had been noted early on that proteins could be cleaved by acid or alkaline hydrolysis, yielding what was later called amino acids. Leucine was the first amino acid isolated after protein hydrolysis (1819) followed in 1820 by the simplest of all amino acids, glycine. A number of more or less brutal methods were used for the degradation of proteins but it was soon realized that acid hydrolysis was the least damaging to the desired end-products, the amino acids. In 1846 Liebig obtained crystals of the first aromatic amino acid, tyrosine. At the end of the 19th century, a dozen amino acids had been isolated in pure form, but the list of 20 standard amino acids in protein was not completed until 1936 when threonine was discovered. 

In another report, a compound assumed to be a polyhydroxylated derivative of an aromatic amino acid isolated from shrimp was demonstrated to function as an antioxidant (Pasquel and Babbitt, 1991). This indicates that there are still many interesting ingredients to be found in the marine environment. 

The earliest references to cinnamic acid, cinnamaldehyde, and cinnamyl alcohol are associated with thek isolation and identification as odor-producing constituents in a variety of botanical extracts. It is now generally accepted that the aromatic amino acid L-phenylalanine [63-91-2] a primary end product of the Shikimic Acid Pathway, is the precursor for the biosynthesis of these phenylpropanoids in higher plants (1,2). 

Ichinose, H., Kurosawa, Y., Titani, K., Fujita, K., and Nagatsu, T. (1989). Isolation and characterization of a cDNA clone encoding human aromatic L-amino acid decarboxylase. Biochem. Biophys. Res. Commun. 164 1024-1030. 

Proteins have been isolated from many cereal seeds that have extensive regions of repeating hexa- to nonapeptides. The consensus repeats are rich in Pro and Gin, and always contain an aromatic amino acid, generally Tyr. The CD spectra of fragments of these proteins containing the repeating sequence have been reported (DuPont etal., 2000 Gilbert... 

In microsomes from Sinapis alba L.,33,34 Tropaeolum majus L.,35,36 and Carica papaya L.,37 the aromatic amino acids (tyrosine and phenylalanine) have been shown to be converted to the corresponding oximes by cytochrome P450-dependent monooxygenases. The conversion of tyrosine to the corresponding oxime in microsomes from S. alba was approximately 1000 fold lower than in microsomes from the cyanogenic sorghum.33 This made a biochemical approach for the isolation... 

PMR studies have been performed on a number of other ribosomal proteins isolated by the acetic acid/urea method (Morrison etal., 1977a). The results of these studies have shown that acedc acid/urea-extracted proteins contain little tertiary structure. However, some structure was seen in protein S4 and especially in protein S16 as indicated by the appearance of ring-current shifted resonances in the apolar region of the spectrum (Morrison et al., 1977b). These are due to the interaction of apolar methyl groups with aromatic amino acids in the tertiary structure of the protein. The PMR spectra were recorded either in water or in dilute phosphate buffer at pH 7.0—conditions under which the proteins were soluble. 

Tyrosine (Tyr or Y) (4-hydroxyphenylalanine ((5)-2-amino-3-(4-hydroxyphenyl)-propanoic acid)) is a polar, neutral, aromatic amino acid with the formula H00CCH(NH2)CH2C6H50H and is the precursor of thyroxin, dopamine, norepinephrine (noradrenaline), epinephrine (adrenaline), and the pigment melanin. Being the precursor amino acid for the thyroid gland hormone thyroxin, a defect in this may result in hypothyroidism. Tyr is extremely soluble in water, a property that has proven useful in isolating this amino acid from protein hydrolysates. The occurrence of tyrosine- 0-sulfate as a constituent of human urine and fibrinogen has been reported. ... 

Phenol is produced through both natural and anthropogenic processes. It is naturally occurring in some foods, human and animal wastes, and decomposing organic material, and is produced endogenously in the gut from the metabolism of aromatic amino acids. Phenol has been isolated from coal tar, but it is now synthetically manufactured (EPA, 2002). Currently, the largest use of phenol is as an intermediate in the production of phenolic resins, which are used in the plywood, adhesive, construction, automotive, and appliance industries. Phenol is also used in the production of synthetic fibers such as nylon and for epoxy resin precursors such as bisphenol-A. 

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