Pterins ions

Recently, we have established the usefulness of C-NMR parameters to detect protonatloii sites In pterldlnes (1,2) and an ex6uiq>le of this work Is given with the stxoicture elucidation of the pterin Ions (Fig. 1). Besides chemical shifts... 

Fig. 5.10. The formula of one of the mononuclear molybdenum cofactors, Moco. Others have a nucleotide phosphate extension (see references to these elements in Further Reading). In sulfide-rich environments, tungsten replaced molybdenum. In some coenzymes, two pterins are bound to the metal ions.

For molecules and molecular ions, such as the cations of 8-methyl-N5-deazapterin and 8-methyl-pterin, the charge distribution (which is represented in MD simulations by a set of discrete atomic charges) will be dependent on the chosen quantum chemical model. Differences in the charge distributions of these cations may influence both the relative binding and solvation thermodynamics. Consequently, we studied the relative solvation thermodynamics of similar DHFR-binding molecular ions.30 Atomic charges... 

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. 2. Molecular model of the eNOS heme domain dimer. Each monomer consists of residues 69-482. The pterin is depicted as a space-filled model and the hemes are the white stick models. The single Zn ion situated at the lower part of the dimer interface is depicted as the white ball. The overall fold is unique to NOS.

Separation was carried out by ion-paired reversed-phase HPLC on a Li-Chrosorb R.P-8 column with a mobile phase of isopropanol-triethylamine-85% phosphoric acid-water (3 10 3 984 v/v) at a final pH of 7.0. The column was eluted isocratically, and the nucleotides were detected at 254 and 287 nm and the pterins at 365 and 446 nm excitation and emission wavelengths, respectively. The separations obtained are shown in Figure 9.133. 

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