PROTEIN METABOLISM 773 



ammonia on glucose, which results in a rich yield of methyl iminazol (v. 

 p. 117). The same grouping is found in creatinine, as is seen by comparing 

 the formula : 



/CH 3 C H 3 



H 2 C Nv HC N<; 



| /C=NH ,1 \CH 



OC NH HC N^ 



Creatinine Methyl-iminazol 



and it is possible that this may furnish a clue to the mode of formation of 

 creatinine in muscle. Creatine has generally been regarded as the primary 

 product of muscular metabolism, but it is possible that the ring-grouping is 

 the original one and that creatine is produced by hydrolysis occurring in this 

 ring. 



The iminazol group is at present chiefly interesting in that it contributes 

 to the formation of the complex ring compounds known as the purines. Since 

 the purine metabolism is closely connected with the question of the origin 

 of uric acid we may consider these questions together. 



