Amino acids, isolation derivatives

Enzymatic Method. L-Amino acids can be produced by the enzymatic hydrolysis of chemically synthesized DL-amino acids or derivatives such as esters, hydantoins, carbamates, amides, and acylates (24). The enzyme which hydrolyzes the L-isomer specifically has been found in microbial sources. The resulting L-amino acid is isolated through routine chemical or physical processes. The D-isomer which remains unchanged is racemized chemically or enzymatically and the process is recycled. Conversely, enzymes which act specifically on D-isomers have been found. Thus various D-amino acids have been... 

Figure 6.1. The role of HMW subunits in gluten structure and functionality. Amino acid sequences derived from direct analysis of purified proteins and the isolation and sequencing of corresponding genes show that the proteins have highly conserved structures, with repetitive domains flanked by shorter nonrepetitive domains containing cysteine residues (SH) available for formation of interchain disulphide bonds. Molecular modelling indicates that the individual repetitive domains form a loose spiral structure (bottom right) while SPM shows that they interact by noncovalent forces to form fibrils (centre right). Includes figures from Parchment et al. (2001) and Humphries et al. (2000).

The stable C isotopic (5 C) signature of organic compounds is commonly employed for source apportionment, but few studies have applied this strategy for specific compounds within DOM. Recently, in an effort to identify specific HMWDOM sources McCarthy et al. (2004) compared the 5 C signature of individual amino acids in HMWDOM to those amino acids isolated from a variety of autotrophic and heterotrophic organisms. Based on patterns of amino acid-specific 8 C values these authors concluded that amino acids in HMWDOM were derived from an autotrophic source. However, this study focused on a Hmited sample set and considerable variations in 8 C signature of amino acids was apparent. 

Calycnlin A (38) is an extraordinary metabolite composed of C28 fatty acid and two y-amino acids isolated from the sponge Discodermia calyx. It is not only highly antifnngal and antitnmor bnt also a potent cancer promoter that was fonnd to be cansed by potent inhibition of protein phosphatases 1 and 2A (1). More than 15 calycnlin derivatives were isolated from several marine sponges, which indicates the involvement of symbiotic microorganisms in the prodnction of calycnhns (6). 

Roughly speaking, methods fall into two classes, based on whether they analyze the individual protein sequence in isolation or whether implications are drawn from a comparison with or among many sequences. Individual sequences are analyzed primarily based on characteristics of amino acids as derived either from physical chemistry or statistically. Such characteristics are hydrophobicity scales or statistical preferences for a particular secondary structure. Section 2.2 will cover these methods. 

R)-Ma ic acid supplies one of the integral stereocenters of hypusine (903), an unusual amino acid isolated from bovine brain. Its name is derived from the two components hydroxyputrescine and lysine (Scheme 132) [195]. 

Peptide WE-14, WSKMDQLAKE LTAE, a 14-peptide possessing N-terminal W and C-terminal E amino acid residues derived from chromogranin A (- chromogranins) and isolated fiom a human Heal... 

Other published statements about the chemical nature of alarm pheromone are not sufficiently precise to provide information on potential non-alarm functions. These include the statement by Ahsan and Prasad (1982) that the alarm pheromone is a polypeptide or protein molecule and the suggestion by Tucker and Suzuki (1972) that the alarm pheromone may be a mixture of peptides, amino acids and derivatives. Similarly Lebedeva et al. (1975) isolated active fractions from minnow skin (Phoxinus phoxinus) but did not identify specific compounds although they found the molecular weight of their active components to be over 950, well above the molecular weight of hypoxanthine-3-oxide. Kasumyan and Lebedeva (1977, 1979) similarly do not provide sufficient detail about the fractions isolated to allow conclusions about other functions for alarm substance. 

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. 

This review has been limited, with a few exceptions, to low-molecular weight compounds with complement activity isolated from plants. Naturally occurring complement modulating compounds such as vitamin A, amino acids and derivatives, copper-chlorophyllin, etc., covered in previous reviews, e.g. by Asghar in 1984 [8], have not been included. 

The charges used for calculations on proteins are best derived using a suitable fragment for each amino acid fleets the environment within the protein (right), rather than the isolated amino acid (left). 

The most suitable synthetic method for these products is the heterocyc-lization reaction of N-thioacyl derivatives of amino acids (202) with phosphorus tribromide (378, 442-450, 559, 560) or anhydrous trifluoroacetic acid (448, 449, 451, 452) (Scheme 103). Treatment of N-thioacyl amino acids with acetic anhydride leads directly to the thiazolylacetate without isolation of an intermediate thiazolinone (365. 452). 2-Alkoxy-derivatives of A-2-thiazoline-5-one, however, can be obtained without acetylation by this method (453, 454). 

The significance of industrial acrolein production may be clearer if one considers the two major uses of acrolein—direct oxidation to acryUc acid and reaction to produce methionine via 3-methyhnercaptopropionaldehyde. In acryUc acid production, acrolein is not isolated from the intermediate production stream. The 1990 acryUc acid production demand in the United States alone accounted for more than 450,000 t/yr (28), with worldwide capacity approaching 1,470,000 t/yr (29). Approximately 0.75 kg of acrolein is required to produce one kilogram of acryUc acid. The methionine production process involves the reaction of acrolein with methyl mercaptan. Worldwide methionine production was estimated at about 170,000 t/yr in 1990 (30). (See Acrylic ACID AND DERIVATIVES AmINO ACIDS, SURVEY.)... 

Biosynthesis. Somatostatin exists in longer forms in several biological tissues (95,96). One of the longer forms, which has been isolated from porcine intestine, has been characterized as a 28-amino acid peptide (97). Somatostatin is derived from a precursor containing 116 amino acids (98,99). The precursor contains one copy of the somatostatin tetradecapeptide, which is contained within the sequence of the 28-amino acid peptide at the carboxy-terminal end of the precursor. The 28-amino acid somatostatin is preceded by a single Arg residue, while somatostatin 1-14 is preceded by a pair of basic residues. 

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