The pattern of breakdown is very different for the two types of nucletide bases, purines and pyrimidines. In the case of pyrimidines the ring is reduced and then opened, and with the exception of beta-alanine the nitrogen is removed by deamination and transamination as ammonia, which must ultimately be converted into urea. However, in the case of purines only the amino nitrogen outside the ring is removed as ammonia. The purine ring itself is oxidized to uric acid by xanthine oxidase and excreted. In humans and primates, the conversion of urate to allantoin occurs non-enzymatically by interaction with oxygen free radicals. free text=Biochemiscal Pathways - An Atlas of Biochemistry and Molecular Biology Edited by Gerhard Michal free text=Color Atlas of Biochemistry by Jan Koolman and Klaus-Heinrich Rohm free text=Human Metabolism by Ramsey Bronk 4.0 inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive inactive Long Name: AMP Synonym: Synonym not specified Accession: S04054 inside SIMPLE_MOLECULE AMP Long Name: Inosine Synonym: Synonym not specified Accession: S04055 inside SIMPLE_MOLECULE Inosine Long Name: Hypoxanthine Synonym: Synonym not specified Accession: S04040 inside SIMPLE_MOLECULE Hypoxanthine Long Name: GMP Synonym: Synonym not specified Accession: S04041 inside SIMPLE_MOLECULE GMP Long Name: Guanosine Synonym: Synonym not specified Accession: S04051 inside SIMPLE_MOLECULE Guanosine Long Name: Guanine Synonym: Synonym not specified Accession: S04039 inside SIMPLE_MOLECULE Guanine Long Name: Xanthine Synonym: Synonym not specified Accession: S04038 inside SIMPLE_MOLECULE Xanthine Long Name: Urate Synonym: Synonym not specified Accession: S04049 inside SIMPLE_MOLECULE Urate Long Name: Allantoin Synonym: Synonym not specified Accession: S04047 inside SIMPLE_MOLECULE Allantoin Long Name: H2O + H+ Synonym: Synonym not specified Accession: S04043 inside SIMPLE_MOLECULE H_sub_2_endsub_O + H_super_+ Long Name: NH4 + Synonym: Synonym not specified Accession: S04052 inside SIMPLE_MOLECULE NH_sub_4_endsub_ _super_+ Long Name: H2O Synonym: Synonym not specified Accession: S04042 inside SIMPLE_MOLECULE H_sub_2_endsub_O Long Name: 5'-AMP Deaminase Synonym: Synonym not specified Accession: P03117 inside PROTEIN p60 Long Name: 5'-Nucleotidase Synonym: Synonym not specified Accession: P03119 inside PROTEIN p61 Long Name: Pi Synonym: Synonym not specified Accession: S04050 inside SIMPLE_MOLECULE P_sub_i_endsub_ Long Name: Ribose 1-Phosphate Synonym: Synonym not specified Accession: S04048 inside SIMPLE_MOLECULE Ribose 1-Phosphate Long Name: Nucleoside Phosphorylase Synonym: Synonym not specified Accession: P03115 inside PROTEIN p62 Long Name: H2O + O2 Synonym: Synonym not specified Accession: S04053 inside SIMPLE_MOLECULE H_sub_2_endsub_O + O_sub_2_endsub_ Long Name: Xanthine Oxidase Synonym: Synonym not specified Accession: P03116 inside PROTEIN p63 Long Name: Guanine Deaminase Synonym: Synonym not specified Accession: P03118 inside PROTEIN p64 Long Name: CO2 Synonym: Synonym not specified Accession: S04046 inside SIMPLE_MOLECULE CO_sub_2_endsub Long Name: Inosine-5'-phosphate Synonym: Synonym not specified Accession: S04044 inside SIMPLE_MOLECULE Inosine-5_super_'_endsuper_-phosphate Long Name: 2H+ + O2 -. Synonym: Synonym not specified Accession: S04045 inside SIMPLE_MOLECULE 2H_super_+_endsuper_ + O_sub_2_endsub_ _super_-_endsuper Long Name: O2 -. Synonym: Synonym not specified Accession: S04056 inside SIMPLE_MOLECULE O_sub_2_endsub_ _super_-_endsuper STATE_TRANSITION 0.3333333333333335,0.0 0.6666666666666667,0.0 a157 a172 a160 a173 a174 STATE_TRANSITION 0.33885863458856313,0.03197380846331699 0.6752151482212028,0.019496224672752138 a159 a168 a157 a171 a170 STATE_TRANSITION 0.3277022854903071,0.006232215297097096 0.6540964401460538,0.010075669939778084 a3 a166 a159 a167 a169 STATE_TRANSITION 0.33333333333333304,-4.440892098500626E-16 0.6666666666666661,-4.440892098500626E-16 a158 a178 a163 a179 a180 STATE_TRANSITION 0.3333333333333335,-8.881784197001252E-16 0.6666666666666667,-8.881784197001252E-16 a163 a181 a162 a182 a183 STATE_TRANSITION 0.3333333333333335,0.0 0.6666666666666665,-8.881784197001252E-16 a162 a184 a161 a185 a186 STATE_TRANSITION 0.33333333333333304,-2.220446049250313E-16 0.6666666666666665,-2.220446049250313E-16 a161 a187 a164 a188 a189 STATE_TRANSITION 0.3333333333333335,-8.881784197001252E-16 0.666666666666667,0.0 a164 a190 a165 a191 STATE_TRANSITION 0.3333333333333332,0.0 0.6666666666666665,0.0 a160 a175 a161 a176 a177