H2O 5-nucleotidase GMP Adenosine H2O H2O P Guanosine Inosine H2O nucleosidase nucleosidase Ribose HN Hypoxanthine (keto form) H2N N H, H20+o H2O (enol form) HO N xanthine H2o+ O2 H2O2 OH HO N Uric acid
excreted by Birds Reptile allantoicase Insects COOH H H Uric acid CHO Glyoxylic acid 2H2O+ urate oxidase CO +ho 2H2N一C-NH2 Cartilaginous fish rea HoN 2H.O 0 Other mammals urease N H 2C0 H H Allantoin Marine invertebrates H2O allantoinase COOH NH Teleost fish Fi The degradation of uric acid to ammonia. The process is arrested at different ONHN stages in the indicated species, and the resulting nitrogen-containing product is excreted Allantoic acid
Gout H2N Guanine HN Xanthine Urate Inhibited by allopurinol OH HN Hypoxanthine
RNA:Cyt、Ura NH N Cytosine Uracil H H 时N-CH2CH2-c.+NH+(O 阝-A anine
RNA：Cyt、Ura
DNA: Th CH Thymine H HN一CH2CH2C+NH+ CHs B-Aminoisobutyric acid
DNA：Thy