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Xanthines, 9-amino

Adenine (6-amino purine) and guanine (2-amino-6-oxy purine), the two common purines, are found in both DNA and RNA (Figure 11.4). Other naturally occurring purine derivatives include hypoxanthlne, xanthine, and uric acid (Figure 11.5). Flypoxanthine and xanthine are found only rarely as constituents of nucleic acids. Uric acid, the most oxidized state for a purine derivative, is never found in nucleic acids. [Pg.329]

Bergmann has suggested that oxidation is ruled out at positions (where hydration occurs readily) which are not accessible to the enzyme after the pteridine is adsorbed on it. Alternatively, the destruction of co-planarity by hydration may prevent adsorption of the pteridine on the enzyme. The case of xanthopterin (2-amino-4,6-dihydroxypteridine) may be relevant. The neutral species of this substance exists as an equilibrium mixture of approximately equal parts of the anhydrous and 7,8-hydrated forms (in neutral aqueous solution at 20°). Xanthine oxidase cataljrzes the oxidation of the anhydrous form in the 7-position but leaves the hydrated form unaffected and about two hours is required to re-establish the former equilibrium. [Pg.41]

A further thirty years were to pass before Kuhn and his co-workers (3) successfully repeated Tswetf s original work and separated lutein and xanthine from a plant extract. Nevertheless, despite the success of Kuhn et al and the validation of Tswett s experiments, the new technique attracted little interest and progress continued to be slow and desultory. In 1941 Martin and Synge (4) introduced liquid-liquid chromatography by supporting the stationary phase, in this case water, on silica in the form of a packed bed and used it to separate some acetyl amino acids. [Pg.3]

The aldehyde oxidoreductase from Desulfovibrio gigas shows 52% sequence identity with xanthine oxidase (199, 212) and is, so far, the single representative of the xanthine oxidase family. The 3D structure of MOP was analyzed at 1.8 A resolution in several states oxidized, reduced, desulfo and sulfo forms, and alcohol-bound (200), which has allowed more precise definition of the metal coordination site and contributed to the understanding of its role in catalysis. The overall structure, composed of a single polypeptide of 907 amino acid residues, is organized into four domains two N-terminus smaller domains, which bind the two types of [2Fe-2S] centers and two much larger domains, which harbor the molybdopterin cofactor, deeply buried in the molecule (Fig. 10). The pterin cofactor is present as a cytosine dinucleotide (MCD) and is 15 A away from the molecular surface,... [Pg.398]

Although it had been assumed that only hypoxanthine dehydrogenase is required for the conversion of hypoxanthine (6-hydroxypurine) into uric acid, in Clostridium purinolyti-cum, two enzymes, both of which contain a selenium cofactor, are required. The enzymes differ in the molecular mass of their subunits, in their terminal amino acid sequences, in their kinetic parameters, and in their specific activities for purines (Self and Stadman 2000). Purine hydroxylase converts purine into hypoxanthine and xanthine (2,6-dihy-droxypurine), which is then further hydroxylated to uric acid (2,6,8-trihydroxypurine) by xanthine dehydrogenase (Self 2002). [Pg.545]

Figure 12 Gradient separation of bases, nucleosides and nucleoside mono- and polyphosphates. Column 0.6 x 45 cm. Aminex A-14 (20 3 p) in the chloride form. Eluent 0.1 M 2-methyl-2-amino-l-propanol delivered in a gradient from pH 9.9-100 mM NaCl to pH 10.0-400 mM NaCl. Flow rate 100 ml/hr. Temperature 55°C. Detection UV at 254 nm. Abbreviations (Cyt) cytosine, (Cyd) cytidine, (Ado) adenosine, (Urd) uridine, (Thyd) thymidine, (Ura) uracil, (CMP) cytidine monophosphate, (Gua) guanine, (Guo) guanosine, (Xan) xanthine, (Hyp) hypoxanthine, (Ino) inosine, (Ade) adenosine, (UMP) uridine monophosphate, (CDP) cytidine diphosphate, (AMP) adenosine monophosphate, (GMP) guanosine monophosphate, (IMP) inosine monophosphate, (CTP) cytidine triphosphate, (ADP) adenosine diphosphate, (UDP) uridine monophosphate, (GDP) guanosine diphosphate, (UTP) uridine triphosphate, (ATP) adenosine triphosphate, (GTP), guanosine triphosphate. (Reproduced with permission of Elsevier Science from Floridi, A., Palmerini, C. A., and Fini, C., /. Chromatogr., 138, 203, 1977.)... Figure 12 Gradient separation of bases, nucleosides and nucleoside mono- and polyphosphates. Column 0.6 x 45 cm. Aminex A-14 (20 3 p) in the chloride form. Eluent 0.1 M 2-methyl-2-amino-l-propanol delivered in a gradient from pH 9.9-100 mM NaCl to pH 10.0-400 mM NaCl. Flow rate 100 ml/hr. Temperature 55°C. Detection UV at 254 nm. Abbreviations (Cyt) cytosine, (Cyd) cytidine, (Ado) adenosine, (Urd) uridine, (Thyd) thymidine, (Ura) uracil, (CMP) cytidine monophosphate, (Gua) guanine, (Guo) guanosine, (Xan) xanthine, (Hyp) hypoxanthine, (Ino) inosine, (Ade) adenosine, (UMP) uridine monophosphate, (CDP) cytidine diphosphate, (AMP) adenosine monophosphate, (GMP) guanosine monophosphate, (IMP) inosine monophosphate, (CTP) cytidine triphosphate, (ADP) adenosine diphosphate, (UDP) uridine monophosphate, (GDP) guanosine diphosphate, (UTP) uridine triphosphate, (ATP) adenosine triphosphate, (GTP), guanosine triphosphate. (Reproduced with permission of Elsevier Science from Floridi, A., Palmerini, C. A., and Fini, C., /. Chromatogr., 138, 203, 1977.)...
The DNA bases that contain amino groups tend to deaminate spontaneously. In particular, cytosine significantly deaminates to uracil, but adenine and guanine can also deaminate to hypoxanthine and xanthine, respectively. If not corrected, the new bases can cause serious mutations... [Pg.240]

Sulfur atom as internal nucleophile. In this area, it has been shown that the reaction of 8-bromo-l,3-dimethyl-7-(2,3-epithiopropyl)xanthine 147 with a range of aliphatic and aromatic amines generates efficiently 2-amino-substituted 2,3-dihydro-thiazolo[2,3-/]xanthine derivatives 148. The process involves a sequential amine-induced thiirane ring opening followed by thiolate z/MYi-substitution of chlorine atom (Equation 66) <1994PCJ647>. [Pg.153]

A plethora of weakly acidic pharmaceutical substances may be titrated effectively by making use of a suitable non-aqueous solvent with a sharp end-point. The wide spectrum of such organic compounds include anhydrides, acids, amino acids, acid halides, enols (viz., barbiturates), xanthines, sulphonamides, phenols, imides and lastly the organic salts of inorganic acids. [Pg.117]

Recently, the possibility to use C60 as anti-inflammatory compound has been reported (Huang et al., 2008). Fullerene-xanthine hybrids have been studied to determine if nitric oxide (NO) and tumor necrosis factor-alpha (TNF-a) production in lipopolysaccharide (LPS)-activated macrophages can be inhibited by hybrid administration, finding positive results. The presence of xanthine moiety seems to be essential for the inhibition of LPS-induced TNF-a production, while the fullerene portion ameliorates the efficiency in LPS-induced NO production blockage, leading to a new promising class of potent anti-inflammatoiy agents. It is necessary to mention also the opposite results obtained by an amino acid fullerene derivative tested on human epidermal keratinocytes at concentration from 0.4 to 400 pg/mL. [Pg.6]

Ring opening of 97 as indicated gives the 9-(a-amino-Q -phenylmethyl) purine 98, which by a base-catalyzed elimination of benzylideneimine is converted into 6,8-diphenyl-2-methylthiopurine 99. This pteridine-purine transformation has a close resemblance to the enzyme-catalyzed ring contraction of tetrahydropteridine into xanthine-8-carboxylic acid (64MI1), in which reaction it was proved by radioactive labeling that it is exclusively C-7 that is expelled. [Pg.65]

The amino groups are replaced with oxygen. Although here a biochemical reaction, the same can be achieved under acid-catalysed hydrolytic conditions, and resembles the nucleophilic substitution on pyrimidines (see Section 11.6.1). The first-formed hydroxy derivative would then tautomerize to the carbonyl structure. In the case of guanine, the product is xanthine, whereas adenine leads to hypoxanthine. The latter compound is also converted into xanthine by an oxidizing enzyme, xanthine oxidase. This enzyme also oxidizes xanthine at C-8, giving uric acid. [Pg.451]

This enzyme [EC 3.5.4.3], also known as guanine amino-hydrolase and guanase, catalyzes the hydrolysis of guanine to produce xanthine and ammonia. [Pg.326]

Dietary purines are not an important source of uric acid. Quantitatively important amounts of purine are formed from amino acids, formate, and carbon dioxide in the body. Those purine ribonucleotides not incorporated into nucleic acids and derived from nucleic acid degradation are converted to xanthine or hypoxanthine and oxidized to uric acid (Figure 36-7). Allopurinol inhibits this last step, resulting in a fall in the plasma urate level and a decrease in the size of the urate pool. The more soluble xanthine and hypoxanthine are increased. [Pg.816]

It undergoes marked self-association and can be purified readily by chromatography on porous glass. The enzyme has a molecular weight of about 89 kDa, a pH optimum of 6.8-7.0, and a temperature optimum of 35°C. Its amino acid composition, its requirement for iron but not for molybdenum and FAD, and the catalytic properties of the enzyme, indicate that sulphydryl oxidase is a distinct enzyme from xanthine oxidase and thiol oxidase (EC 1.8.3.2). [Pg.249]

GMP catabolism also yields uric acid as end product. GMP is first hydrolyzed to guanosine, which is then cleaved to free guanine. Guanine undergoes hydrolytic removal of its amino group to yield xanthine, which is converted to uric acid by xanthine oxidase (Fig. 22-45). [Pg.874]


See other pages where Xanthines, 9-amino is mentioned: [Pg.556]    [Pg.80]    [Pg.318]    [Pg.923]    [Pg.923]    [Pg.116]    [Pg.57]    [Pg.321]    [Pg.322]    [Pg.466]    [Pg.87]    [Pg.544]    [Pg.149]    [Pg.241]    [Pg.212]    [Pg.80]    [Pg.168]    [Pg.194]    [Pg.10]    [Pg.292]    [Pg.95]    [Pg.285]    [Pg.139]    [Pg.90]    [Pg.197]    [Pg.377]    [Pg.165]    [Pg.406]    [Pg.584]    [Pg.949]    [Pg.33]    [Pg.304]    [Pg.99]    [Pg.481]   


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