Structure of Pterins

Figure 15.1 Structure of pterin. In the folates, pterin is linked to 4-aminobenzoic acid through at methylene bridge at posirion 6.

Flgure 1 Structure of pterin co factor found in tungstoenzymes such as P. furiosus AOR... 

For a long time before the ring structure of pterins was known, compounds containing the pteridine ring were being prepared. In 1895, 2,4-dihydroxy-pteridine was prepared by oxidation of tolualloxazine and decarboxylation of the resulting 2,4-dihydroxypteridine-6,7-dicarboxylic acid, and the same compound was prepared in 1907 by the action of hypobromite on pyrazine-2,3-dicarboxamide. The condensation of 4,5-diaminopyrimidine and benziF to form 6,7-diphenylpteridine reported in 1906 was the first example of the most versatile general method of pteridine synthesis. 

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,... 

Raman, C. S., Li, H., Martasek, P., Kral, V., Masters, B. S., Poulos, T. L., Crystal structure of constitutive endothelial nitric oxide synthase a paradigm for pterin function involving a novel metal center, Cell 95 (1998),... 

Figure 17.2 The structure of the pterin cofactor (1) which is common to most molybdenum- and tungsten-containing enzymes and schematic active site structures for members of the xanthine oxidase (2,3), sulfite oxidase (4) and DMSO reductase (5-7) enzyme families. (From Enemark et al., 2004. Copyright (2004) American Chemical Society.)...

Fig. 8. Comparison of the pterin-bound and -free structures. In the absence of pterin with the SEITU inhibitor in the active site (right), L-Arg binds in the pterin site. L-Arg is an excellent mimic for H4B owing to the similar H-bonding pattern with the heme propionate and Serl04, and the ability of the L-Arg guanidinium group to aromatically stack with Trp449.

Amidinium type resonance determines protonation sites also in some more complex systems, such as cytosine [74] and pterin [75]. Cytosine is protonated on the ring nitrogen N-1 (Katritzky and Waring, 1963) and calculations on the electronic structure of the cation have been published (Denis and Gilbert, 1968). Pterin is... 

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