Pterins amino

Aminopteridine is the most sensitive to acid hydrolysis, and 6-amino- and 6-dimethyl-amino-pteridine are also hydrolyzed, even by cold 0.0IN hydrochloric acid, too rapidly for accurate determination of the cation form (52JCS1620). 2-Amino- and 4-amino-pteridine are not readily attacked by IN HCl at 20 °C but at 100 °C the former compound is destroyed and the latter converted into pteridin-4-one (5UCS474). 2,4-Diaminopteridine can be hydrolyzed by refluxing in 6N HCl for 30 minutes to 2-aminopteridin-4-one (pterin 2) and after... 

Various 6- and 7-methyl- and 6,7-dimethyl-pteridines bearing either oxo or amino groups in the 2- and 4-positions can be oxidized to the corresponding carboxylic acids by alkaline potassium permanganate on heating. Various lumazine and pterin mono- and di-carboxylic acids have been prepared in this way (48JA3026, 78CB3790). 

Pterin, 4-amino — see Folic acid, 4-amino-4-deoxy-Pterin, 6-amino-structure, 3, 276 Pterin, 7-amino-structure, 3, 276 Pterin, 6-arylthio-reactivity, 3, 299 Pterin, 6-(l-carboxyethoxy)-synthesis, 3, 309 Pterin, 6-carboxy-7-hydroxy-properties, 3, 277 Pterin, 7-carboxy-6-hydroxy-properties, 3, 277 Pterin, 6-chloro-nucleophilic substitution, 3, 292 synthesis, 3, 290... 

Pterin-4-one, 2-amino-stnicture, 3, 273 Pterin-7-one, 2,4-dimethoxy-hydrolysis, 3, 299 Pterin-6-ones reactions... 

Pterin-dependent amino acid hydroxylases 96CRV2659. 

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,... 

D. desulfuricans is able to grow on nitrate, inducing two enzymes that responsible for the steps of conversion of nitrate to nitrite (nitrate reductase-NAP), which is an iron-sulfur Mo-containing enzyme, and that for conversion of nitrite to ammonia (nitrite reduc-tase-NIR), which is a heme-containing enzyme. Nitrate reductase from D. desulfuricans is the only characterized enzyme isolated from a sulfate reducer that has this function. The enzyme is a monomer of 74 kDa and contains two MGD bound to a molybdenum and one [4Fe-4S] center (228, 229) in a single polypeptide chain of 753 amino acids. FXAFS data on the native nitrate reductase show that besides the two pterins coordinated to the molybdenum, there is a cysteine and a nonsulfur ligand, probably a Mo-OH (G. N. George, personal communication). 

Pterins — These are pigments derived from pteridine skeletons. All natural pterins are 2-amino-4-hydroxypteridines bearing various substituents at Cg and C7 and having different oxidation states of N5 and Ng. 

A new synthesis of pterins based on the acylation of 4-amino-5-nitrosopyrimidines with dienoic acid chlorides, followed by a high-yielding intramolecular hetero DA cycloaddition and cleavage of the N—O bond has been reported <06HCA1140>. Several new substituted pterins have been obtained in an efficient one-pot procedure using N,N dimethyldichloromethyleniminium chloride (phosgeniminium chloride) and a suitable pyrazine <06H933>. 

Another factor that characterizes molybdenum and tungsten enzymes is that instead of using the metal itself, directly coordinated to amino acid side-chains of the protein, an unusual pterin cofactor, Moco, is involved in both molybdenum- and tungsten-containing enzymes. The cofactor (pyranopterin-dithiolate) coordinates the metal ion via a dithiolate side-chain (Figure 17.2). In eukaryotes, the pterin side-chain has a terminal phosphate group, whereas in prokaryotes, the cofactor (R in Figure 17.2) is often a dinucleotide. 

Fig. 6. The active site architecture of eNOS in the A subunit. L-Arg is held in place by several H-bonds with conserved groups. The H4B is sandwiched between aromatic groups contributed from each subunit Trp449 in subunit A and Phe462 in subunit B. Note that the amino group of L-Arg and the pterin donate an H-bond to the same heme propionate, which helps to understand the observed interdependence of pterin and substrate binding. The schematic diagram illustrates the extensive contacts between pterin and protein groups in each subunit.

---