Pteridines, unconjugated

Nl). This line of inquiry is likely to become more active if the unconjugated pteridine, biopterin, proves to have the proper microbiological activity and so can serve as standard. 

Subsequent studies by the same group (W7) have shown that the increased endogenous fluorescence in patients with chronic renal failure is due to the unconjugated pteridine, xanthopterin (2-amino-4,6-pteridinedione, 179 Da see Table 4 and Figs. 10 and 11) (B23, Dll, L15, Pll). Unlike the conjugated pteridines (folates), the function of many of the unconjugated pteridines (pterins) has yet to be elucidated (U2, Z3). So far only biopterin has been shown to have a defined role, being a cofactor in the hydroxylation of several aromatic amino acids involved in the formation of neuronal hormones such as catecholamines and serotonin. 

Several studies have shown altered catecholamine metabolism in uremia and have suggested that the unconjugated pteridines may play a role in the causation of some of the neurological symptoms (C21, D8). Dhondt and Vahille have reported an increase of the pteridines neopterin and biopterin in the serum of maintenance dialysis patients (D12). They did not, however, describe an accumulation of xanthopterin, perhaps because this compound, unlike the blue-fluoresc-ing pteridines (excitation maxima = 360 10 nm), has its maximum excitation at 390 nm. 

Unconjugated pteridines, which lack a p-aminobenzoylglutamic acid residue, are of interest because they can be formed by the oxidative transformation of reduced folate derivatives moreover, pteridines in biological fluids are elevated under certain pathological conditions (McCormack and Newman, 1985). 

More knowledge of pterinoids means renewed hope of solving such old clinical problems as the pathogenesis of sprue. Increased interest, too, attaches to the unconjugated pterins in the body Are they increased or diminished in some diseases The effectiveness of antifolics in the palliative treatment of leukemia is halted by toxic symptoms and, eventually, by drug fastness this emphasizes the need to explore pteridine metabolism to find new opportunities for chemotherapy aimed at pterinoid targets. 

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