Aromatic amino acids, chemical structure

Arginine, 2D biosynthesis, 435 catabolism, 431 134 chemical structure, 20 plasma concentration, 465 Argininosuccinate lyase, 439 Acgininosuccinate synthase, 439 Aromatic amino acids, chemical structure, 19 Arsenate, 840 Artenosclcrosis, 357 Arteriovenous differences, 19 199 Artery, physiology, 359 Ascoitale... 

The precise chemical interactions between an adhesin and its receptor are also important. For example, direct- and water-mediated hydrogen bonds are the most important interactions within the carbohydrate-recognition domain in carbohydrate-binding adhesins on the host cell surface (Weis and Drickamer, 1996). Nonpolar van der Waals interactions and hydrophobic "stacking of the receptor oligosaccharide rings with aromatic amino acid side chains of the bacterial adhesin protein also contribute to oligosaccharide-protein interactions. X-ray structural... 

As a result of a high index of clinical suspicion and, on occasion, supporting biochemical data from other investigations, one of the first specialist investigations to ascertain whether a patient has an inborn error of biogenic amine metabolism is, as mentioned above, analysis of the CSF concentrations of HVA and 5HIAA. This is often performed in conjunction with the measurement of 3-methyldopa (3-MD), also known as 3-methoxytyrosine. 3-MD is formed from L-dopa via COMT activity and accumulates in conditions where aromatic amino acid decarboxylase activity is impaired. The chemical structures of HVA, 5HIAA and 3-MD are shown in Fig. 6.2.1. 

The vertebrate hormones. The principal established vertebrate hormones are listed in Tables 30-1 and 30-2. Also given are references to other parts of the text, where specific hormones are discussed. The hormones can be divided into four groups on the basis of chemical structure (1) peptides and proteins, (2) derivatives of the aromatic amino acids, (3) steroids and prostaglandins, and (4) volatile compounds such as NO and CO. The most numerous are the peptide hormones, many of which also act as neurotransmitters. Peptide hormones, e.g., those with insulinlike effects, function in all phyla of the metazoa, and hormone-like molecules are found in bacteria.24... 

Fig. 1. A. Chemical structure of key molecules involved in the key steps in intracerebral synthesis and metabolism of dopamine. The successive steps are regulated by the enzymes tyrosine hydroxylase (TH), aromatic amino acid decarboxylase (AADC), monoamine oxidase (MAO) and dopamine-p-hydroxylase (DBH). B. Structure of key toxins and other drugs acting on dopamine neurones, including 6-hydroxydopamine (6-OHDA), a-methyl tyrosine, and amphetamine. For further details see Iversen and Iversen (1981) or Cooper et al. (1996).

Incorporation of fluorine into peptides and proteins is usually achieved through biosynthetic routes, chemical synthesis, or a combination of these two methods. Each method has its own advantages and shortcomings, but each requires a 19F-labeled amino acid. The most commonly used ones are commercially available analogues of aromatic amino acids, such as tryptophan, phenylalanine, tyrosine, and phenylglycine. Aliphatic 19F-labeled amino acids are not commonly available and usually have to be synthesized. The synthesis of most fluorinated amino acids is described in detail in the literature [1, 9,10], For structure analysis of peptides and proteins, it is important that (i) the fluorine label is rigidly attached to the peptide backbone, (ii) the label does not alter the structure or function of the peptide, (iii) the extent of fluorination is restricted to avoid multiple signals, and (iv)... 

ABSTRACT This article describes recent developments in the chemistry of an important family of complex monosaccharides which have diverse structures and participate in a wide range of biological processes. For example 3-deoxy-D-/n nno-2-octulosonic acid (KDO) is a key component of the lipopolysaccharides (LPS) of Grammnegative bacteria, 3-deoxy-D-araftmo-2-heptulosonic acid (DAH) is a key intermediate in the biosynthesis of aromatic amino acids in bacteria and plants. A number of their syntheses that were achieved by homologation reactions of the natural carbohydrate units using enzymatic or chemical methods, as well as by total synthetic approaches are here included. Special emphasis is placed on new methodologies and their correlation with the biosynthetic pathway of the corresponding ulosonic acids. 

Chart 8.2 Chemical structures of aromatic amino acids. 

Presently, alkaloids are classified into three main categories as shown in Fig. 8.2 [6]. This chemical classification of alkaloids is universally adapted and mainly depends on the type of heterocyclic ring structure present (Fig. 8.3). Alkaloids are further classified according to the amino acids (or their derivatives) from which they originate (Fig. 8.4) [6]. The most important classes are derived from the amino acids, ornithine and lysine, or from the aromatic amino acids, phenylalanine and tyrosine, or from tryptophan and a moiety of mavelonoid origin. A number of alkaloid-based compounds are also derived from anthranilic acid or from nicotinic acid. 

The book comprises six chapters and the first of these is devoted to a description of the steps in the pathway which lead from carbohydrate to the individual aromatic amino acids and the manner in which the differing strategies of control of the flow of metabolites are exercised. One chapter discusses the chemistry of important intermediates on the pathway and draws attention to the ways in which specifically isotopically labelled precursors may be prepared. The remaining four sections describe the numerous and structurally diverse metabolites which are derived from the aromatic amino acids or from intermediates in the pathway. Identical compounds in the chemical sense are often synthesised in different ways in different... 

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