Isolation from proteins

Amino acids isolated from protein hydrolysates. 

An interesting and important fact is that almost all amino acids isolated from proteins L-configuration have the L-configuration at the a-carbon, although some amino acids isolated from microbiological sources are the mirror image isomers, ie in the D-configuration. We shall consider amino add stereochemistry in more detail in section 8.3. 

Recall the importance of the amino-acids as units from which the proteins are built up. What amino-adds have hitherto been isolated from proteins by digestion and by acid hydrolysis ... 

Historically, L-aspartic acid was produced by hydrolysis of asparagine, by isolation from protein hydrolysates, or by the resolution of chemically synthesized d,L-aspartate. With the discovery of aspartase (L-aspartate ammonia lyase, EC 4.3.1.1),57 fermentation routes to L-aspartic acid quickly superseded the initial chemical methods. These processes are far more cost effective than the fermentation routes, and aspartate is now made exclusively by enzymatic methods that use variations of the general approach outlined in Scheme 2.19.53-57-65... 

Sometimes chemists need the unnatural D enantiomer of an amino acid, often as part of a drug or an insecticide. Most L-amino acids are isolated from proteins, but the D-amino acids are rarely found in natural proteins. D-amino acids can be synthesized from the corresponding L-amino acids. The following synthetic scheme is one of the possible methods. 

We have found that 1) volatiles from protein hydrolysates will attract fruit flies of various species, both male and female, 2) that volatiles from protein hydrolysates Which had been brought to pH 9 are more attractive than volatiles from protein hydrolysate as it comes at pH 4.2, 3) that Isolates from protein hydrolysates are attractive to various species of fruit flies, and 4) that the basic isolate is attractive to male oriental fruit flies. We are continuing to pursue vigorously the Isolation, identification, and biological testing of the active components of this mixture. 

Hydrolysis of proteins without taste by proteases often produces bitter peptides. Hydrophobic amino acid residues located in the interior of protein molecules in aqueous solution are exposed by fragmentation of the protein molecules treated with proteases, and the peptides containing a number of hydrophobic amino acid residues occur in the solution (13). Many bitter peptides as shovm in Table 4-have been isolated from protein digests with proteinases (14-22). 

Derivation Isolated from proteins after hydrolysis with alkali. 

The two purposes of separation of amino-acid and peptide mixtures are either at the preparative level, to isolate one or more individual components from the mixture for further study or at the analytical level, to identify and to determine the relative amounts of some or all of the components. Most of the routine studies, conducted daily to determine the amino-acid content of clinical and botanical samples in hundreds of laboratories around the world, are at the analytical level. However, many of the research studies are at the preparative level an example of this is the identification of crosslinking amino acids from proteins, through their isolation from protein hydrolysates, from physiological specimens for medical investigations, or purely to gain new knowledge. 

By continuing this condensation a very large molecule, known as a peptide, can be built up in which the group —NH.CO.CHj— is repeated very many times. Peptides are degradation products of proteins and therefore of a similar but somewhat less complex structure. Glycine is the simplest a amino acid, but as many as thirty others have been isolated from proteins of which four examples are ... 

The proteins of the body are made up of some combination of twenty different subunits called a-amino acids. The general structure of an a-amino acid is shown in Figure 19.1. We find that nineteen of the twenty amino acids that are commonly isolated from proteins have this same general structure they are primary amines on the a-carbon. The remaining amino acid, proline, is a secondary amine. 

General structure of an a-amino acid. All amino acids isolated from proteins, with the exception of proline, have this general structure. 

First, many of these antibiotics, after their discovery, characterization and evaluation, were not of sufficient practical importance and work on them was discontinued. Second, they have relatively complicated structures. Unlike the peptide hormones, which are composed of a limited number of natural amino acids found in proteins, many peptide antibiotics contain a large variety of components other than amino acids. Besides the frequently occurring amino acids not isolated from proteins Table 1.1), many other components, such as hydroxy acids, amino sugars, fatty acids, pyrimidine derivatives and so on, are present Table 1.2). They also often contain unusual peptide linkages, unknown in proteins. Furthermore, most of the peptide antibiotics are of cyclic nature and for this reason are resistant to enzymatic attack, which makes their structural elucidation in many instances more complicated. 

The appended list gives the polypeptides which have so far been isolated from proteins and therefore of the combinations of amino acids which occur in the protein molecule —... 

Deduce the structure of valine. Natural valine that is isolated from proteins has a specific rotation [a] of +26°. What is the rotation of the valine prepared by the Hell-Volhard-Zelinsky method ... 

Acidic and basic amino acids, like glutaric acid, aspartic acid and lysine, are also isolated from protein hydrolysates for artificial nutrition. The fractions are filtered off under sterile conditions and further purified by crystallisation. Since the BSE crisis, the supply with amino acids has come under scrutiny manufacturers had to assure regulators and customers likewise, that their starting material does not originate from cattle. Mostly used are poultry feathers and pork gelatine. [62]... 

Recent evidence indicates that various prenyl groups can be attached to proteins. Both famesyl and geranylgeranyl groups have been isolated from proteins (Epstein et al., 1990). 

Four main processes are distinguished in the production of amino acids chemical synthesis, isolation from protein hydrolysates, enzymatic and microbiological methods of production, which is currently the most important. The following sections will further elucidate the important... 

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