CHAPTER LXX 

 THE METABOLISM OF PROTEIN (Cont'd) 



CREATINE AND CREATININE 



Creatine and creatinine are very largely products of endogenous metab- 

 olism; they are mainly derived from chemical processes occurring in 

 the tissues although some of the creatine and creatinine present in the 

 food may appear as creatine in the urine. 



Essential Chemical Facts 



Before we proceed further with a discussion of the metabolism of 

 these important substances, it will be necessary to refer briefly to some 

 points in their chemistry. The simpler of the two bodies is creatine, 

 which is methyl-guanidine-acetic acid; creatinine is its anhydrid, being 

 formed from creatine by the removal of a molecule of water, so that the 

 NH 2 groups become joined together in the same way as they do in the 

 formation of peptides from amino acids (page 599). The relationships 

 are illustrated in the following formulas: 



(methyl) 

 CH 3 N 



/ \ 



/ CH.COOH 



NH C - H 2 O 



\ (acetic acid) 



(guanidine) NH 2 



(creatine) 



CH 3 -N-CH-CO 



i i 



I ! 



NH=zC 



\ 



\ ! 

 \ I 



NH 



(creatinine) 



It should be noted that guanidine is closely related to urea 

 NH 2 



/ 



(0=C ), and that when creatinine is formed from creatine a ring 



NH 2 



622 



