101. PATHWAYS OF PURINE AND PYRIMIDINE NUCLEOTIDE CATABOLISM 



BucleotldeB are com^aei of a purine or pyrtmldlne base linked to a pentose or desoxypen- 

 tose sugar which, in turn. Is linked to phosphate . Removal of the phosphate leaves a com- 

 pound designated as a nucleoside. See table 102 for pathways of nucleoprotein catabolism 

 in general. 



A = Phosphatase; B = Adenylic acid deaminase; C « Adenosine deaminase; D = Adenafle?- 

 E = Nucleoside phosphorylaae ; F - Xanthine oxidase; G = Guanylic acid deaminase; H - 

 Guanosine deaminase; I ^ Guanase; J = Phosphorylase or hydrolase; K = Cytidine deam- 

 inase; L = Cytosine deaminase; M = Uracil- thymine oxidase; H = Barbiturase; = Urease 



NUCLEOTIDES 



NUCLEOSIDES 



BASES 



Adenylic Acid' 



A *• 



Adenosine 1 



? »• 



Adenine^ 



Inosinic Acid' 



Inosine' 



D' 



Hypoxanthine^ 



Xanthylic Acid' 



Xanthosine' 



Xanthine 



Guanylic Acid' 



Guanosine' 



Guanine^ 



Thymidylic Acid^ 



Thymidine^ 



Thymine 



Cytidylic Acid^ 



Cytidine^ 



~ 



Cytosine* 



Uridylic Acid^ 



Uridine^ 



i^^ 



I 



UracU'' 



Barbituric 

 Acid^-^ 



3-Alanine 



j^ 



Malonic Acid 



Urea' 



Water 



3j: 



T 

 -O- 



Carbon Dioxide 



Ammonia 



/I/ A purine derivative or contains purine ring, /a/ A purine. /}/ A pyrlmidine derivative or 



Srl^ ^/Z^ barbituric acid. /7/ Pathway de,»onfltrated with Corynebacterlum and Hycibac- 

 ^ltZ:.ii'J^ ^^ ^r"^"' °^*'^^ "^^""-^ (thymine) yields e-aminolsobutyrlc acid. ^/ via- 

 uric acid, allantoic acid, and glyoxylic acid. (cf. table 102). /lo/ Urea is excreted as the 



IdL'^^a^,? "f"" Tt -*-^"''" ^y >»™-l«, and as an ind product ^f pu^lnel^d Tj^ 

 idlne metabolism by most fishes, aajihlbia and fresh water lamelllbranchs . 



181 



