Amino nonprotein

The presence of many nonprotein amino acids has been reported in various living metaboUtes, such as in antibiotics, some other microbial products, and in nonproteinaceous substances of animals and plants (7). Plant amino acids (8) and seleno amino acids (9) have been reviewed. 

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). ... 

In addition to the twenty amino acids commonly found in proteins, two others—selenocysteine and pyrrolysine—are found in some organisms, and more than 700 nonprotein amino acids are also found in nature. y-Amino-butyric acid (GABA), for instance, is found in the brain and acts as a neurotransmitter homocysteine is found in blood and is linked to coronary heart disease and thyroxine is found in the thyroid gland, where it acts as a hormone. 

Figure 1. Structures of some nonprotein amino acids isolated from plants...

In mammals, peptide hormones typically contain only the a-amino acids of proteins finked by standard peptide bonds. Other peptides may, however, contain nonprotein amino acids, derivatives of the protein amino acids, or amino acids finked by an atypical peptide bond. For example, the amino terminal glutamate of glutathione, which participates in protein folding and in the metabolism of xenobiotics (Chapter 53), is finked to cysteine by a non-a peptide bond (Figure 3—3). The amino terminal glutamate of thyrotropin-... 

From this brief review of marine vertebrate venoms, it is obvious that very few biochemical investigations have been done. The technology to study marine vertebrate venom components is available. There are simply not enough scientists interested enough to enter the field. The first task is to isolate the toxic principles and identify the amino acid sequences. Pharmacological investigation should be done on the purified toxic principle and not on the crude venom, which is a mixture of many proteins and nonproteins. 

Antibiotic effects of nonprotein amino acids have not been studied in much detail with soil microorganisms. The organs of legumes alone contain more than 300 nonproteinogenic amino acids, such as methylene-glutamine, common to all... 

Table 3 Susceptibility of Yeast Species and Bacterial Strains from Pea Seedlings Against the Heterocyclic Nonprotein Amino Acid P-I.soxylinonyl-Alanine (PlA) ...

Nonprobability sampling, 26 1001 Nonproduct contact utilities, 11 45-46 Nonprotein amino acids, 2 554 Nonprotein nitrogen (NPN), 10 865 Nonquenching photoluminescence properties, 26 804-805... 

Some recovery problems encountered during hydrolytic extraction of amino acids from environmental samples were discussed. A way was proposed for compensating for differential losses of neutral, acidic and basic amino acids, consisting of adding various nonprotein amino acids before the hydrolysis, that act as charge-matched recovery standards131. 

From the amino acid data in Table 8.2, protein N was calculated to make up 36, 40.46 and 45 % of the total N in the arctic, cool temperate, subtropical and tropical soils, respectively, averaging 42 %. Thus, about 58 % of the total N in soils was nonprotein. Amino sugars in the soils constituted between 4.5 and 7.4% of the total N, with soils under warmer climates containing more amino sugars than those under cooler dimates. 

Kataoka (1997) describes a method for the analysis of 21 protein amino acids and 33 nonprotein amino acids with NPD detection. One disadvantage of this method is the use of diazomethane, which is explosive and toxic (Kataoka, 1997). A method for homocysteine with GC-FID analysis uses a one-step derivatization with ethyl chloroformate and an extraction procedure (Husek et al., 2003). 

For the purpose of this chapter, all amino acids containing side chains that differ from the L-a-amino acids will be designated as either unusual or nonprotein amino acids. This is due to the observation that these unusual amino acids are generally not found to be the constituents of proteins. The scope of this chapter is limited to nonprotein L-a-amino acids. The definition of nonprotein amino acid is not absolute and, therefore, the... 

There is also a significant occurrence of nonprotein D-amino acids in nature.These amino acids have attractive structural variations and remarkable biological properties. However, this chapter will not include details on nonprotein D-amino acids. Selenium-containing amino acids, such as selenocysteine and selenomethionine, are also considered as unusual amino acids. Recently, much interest in selenium-containing amino acids has emerged. More information about selenium-containing amino acids is available in Chapter 5.05. 

According to the report by Bell et al. there are about 800 nonprotein amino acids known to date in the literature. It is not practical to cite all the primary literature of the reported nonprotein amino acids. To the best of our knowledge, we have tried to cite the most relevant references and the recent review papers available. In most cases, further references for the primary literature can be obtained from these reviews. We apologize to the reader for any missed compounds and citations that might be relevant to the material. 

When the biosynthetic pathways given above are examined, it is apparent that several intermediates are indeed nonprotein ct-amino acids. Ornithine, homoserine, homocysteine, and ct-e-diaminopimelic acid are a few examples. This shows that some nonprotein amino acids originate as intermediates during the biosynthesis of... 

In addition to this, it has been reported that nonprotein amino acids could be formed by structural modifications to protein amino acids (methylation, hydroxylation, and halogenation) through modified L-a-amino acid biosynthetic pathways and through novel biosynthetic routes. Some examples of the nonprotein amino acids derived through these biosynthetic pathways are given below (Figure 3). A detailed discussion of known biosyntheses for certain nonprotein amino acids will be discussed later in this chapter. 

Figure 3 Nonprotein amino acids (a) 5,5,5-trichioroieucine, (b) coronamic acid, and (c) 4-OH-phenylglycine.

Earlier in this chapter, it was mentioned that many of the nonprotein amino acids are components of nonribosomal peptides. During such a biosynthesis, the peptide is attached to a carrier protein through a thioester bond, until chain termination occurs and the final product is released. The carrier protein is posttranslationally modified by the attachment of a phosphopantetheinyl group from coenzyme A. This step gives rise to the active carrier protein with a phosphopantetheine arm upon which amino acids are added to during NRPS. As an example, loading of isoleucine onto the carrier protein is depicted below (Scheme 5). Further details about nonribosomal peptide syntheses and enzymatic reactions can be found in Chapter 5.19. 

During the biosynthesis of nonribosomal peptides, there are two ways to incorporate the nonprotein amino acids. They can be incorporated either as a single unit or as an L-a-amino acid, which then undergoes structural modifications, while attached to the carrier protein. In the case of coronamic acid, L-rr//o-isoleucine is loaded onto the carrier protein and a unique biosynthetic pathway produces a cyclopropyl group containing a nonprotein amino acid. Specific examples of the biosynthesis of nonprotein amino acids will be discussed in the following sections. 

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