50 



Adenin is 6-amino-purin, C 5 H 3 N 4 NH 2 , the amino grouping being 

 in the 6 position of the purin ring. Graphically expressed it is 



HC C NH V 



I X CH 



Guauin, C 5 H 3 N 4 2 , is 2-amino-6-oxypurin, or 

 HN CO 



H 2 N.C C NH X 



' II II X CH 



N C N/ 



Besides being found as a product of hydrolysis of nucleoprotein, 

 it is foiind in small quantity in muscles and also in the scales of fishes 

 Hypoxanthin, C 5 H 4 N 4 O, is 6-oxypurin, or 



HN -- CO 



HC C NH 



II II CH 



N - C N 



It is obtained from adenin by " deaminization," the replacement 

 of the NH 2 group by an atom of oxygen. This takes place in the body 

 as the result of the action of an enzyme known as adenase : 



C 5 H 3 N 4 NH 2 + H 2 = C 5 H 4 N 4 + NH 3 . 



Hypoxanthin is also found in the muscles. It is abundant in the 

 sperm of certain fishes, such as the salmon and the carp. It also 

 occurs in small quantities in bone marrow, in milk, and in urine. 



Xanthin, C 5 H 4 N 4 2 , is 2, 6, dioxypurin, or 



HN CO 



OC C NH 



CH 



NH- 



It bears the same relationship to guanin as hypoxanthin does to 

 adenin. In the body the enzyme guanase converts guanin into xanthin. 

 Oxidizing enzymes also possess the power of converting hypoxanthin 

 to xanthin by adding on an atom of oxygen. 



Uric acid is trioxypurin ; its chemical relationships are discussed 

 fully later (see p. 458). 



Derived Proteins : Acid and Alkali Metaprotein may be pre- 

 pared by treating a solution of egg white with a little dilute acid 

 (10 per cent. HC1) or dilute alkali at body temperature for five minutes, 

 and then heating up to the boiling-point. The metaprotein thus 

 formed differs from the original egg albumin in not being coagulated 

 "by heat while in the acid or alkaline solution, and in being precipitated 

 (salted out) by half -saturation with ammonium sulphate (see table 



