Pteridyl aldehyde

The organization of xanthine oxidase appears to be quite complex. There is evidence that various substrates are not bound at the same site, and that the primary reaction of different substrates may occur with various ones of the cofactors. The oxidation of purines and aldehydes is inhibited by pteridyl aldehyde and by cyanide, but these reagents do not affect the oxidation of DPNH. It is possible that these inhibitors influence substrate binding sites and primary electron transport, respectively, and that the oxidation of DPNH involves a different binding site and avoids the cyanide-sensitive electron transport mechanism, which may well involve iron. Xanthine oxidase, and probably all flavoproteins, require —SH groups, but a definite function for these groups cannot be ascribed at this time. Similarly, various factors influence the reactions with oxidants differentially. Cyanide inhibits cytochrome reduction, but not the reactions with 0 or dyes. Reduction of either cytochrome c or nitrate depends upon the presence of molybdenum. These observations... 

Several possibilities come to mind. One is that the sulfonamide actually forms a pteridinyl derivative such as I, which in turn may tend to reduce the availability of the pteridyl pyrophosphate ester D, and decrease the production of G. A condensation product of sulfamethoxazole and the pteridyl alcohol B was actually obtained, raising the possibility of a sulfonamide-containing imposter of dihydropteroic acid arising. A second viable possibility is to consider a tautometric equilibrium between the pteridine alcohol B and the aldehyde form C, which will very likely form the Schiff base derivative J, with the p-amino function of a sulfonamide. This would also lead to a pteridyl alcohol depletion from the path of the FH2 synthesis (Seydel, 1968). 

Liver aldehyde oxidase, IX, 119 Liver L. casei factor (N-(4- [(2-amino-4-hydroxy-6-pteridyl)methyl amino) benzoyl]-f(-f-)-glutamic acid), see also under Folic acid and teroylglu-tamic acid... 

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See also in sourсe #XX -- [ ]

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