THE METABOLISM OF PRO! 



probably effected bj many of the tissues of the body and certainly by 

 the blood, the active agency in all cases being no doubt an enzyme. That 

 the blood contains snch an enzyme is indicated by tin- fact that creatine 

 is transformed to creatinine by ]»!<»<" I Bernm more quickly than it is 

 when merely dissolved in water. Even heated blood serum po 

 some of this power. The liver also probably brings about the transfor- 

 mation, as lias been shown by perfusion experiments, ami by ti 

 that in cases of phosphorus or hydrazine poisoning creatine < 1 i -^ j » 1 . 

 creat inin< in t he urine. 



The problem therefore narrows itself down to the question of the 

 origin of creatine. In the light of chemical knowledge then 

 precursors from which creatine might be formed. One, sample, is 



arginine, which it will be remembered is guanidine-amino-valerianic acid 

 page 605 . By oxidation this might become changed into guani- 

 dine-amino-acetic acid, which by methylation would then be changed into 

 creatine. That, snch a process of methylation may actually occur in the 

 animal body is definitely known, for it happens when such substai 

 pyridine or naphthalene are given with the food. They appear in the 

 urine as methyl derivatives. The possibility of the derivation <■ tine 



from arginine is not, however, borne ou1 by the result of the injection of 

 arginine, for such injection does not increase the creatinine in the urine. 

 The closely related substance, guanidine-acetic acid, when fed to animals 

 (rabbits does cause a slight increase in the excretion of creatine (Jafl 

 and also, it is said, an increase in the creatine content of the i 

 Even in this case, however, by far the largest proportion of the admin- 

 istered guanidine-acetic acid is excreted in the urine unchanged. 



The Large percentage of creatine in muscle tissue leads one to exp 

 that some relationship must exist between muscular metabolism and the 

 amount of creatine present either as such in the muscles or itinine 



in the urine. Regarding the latter point it is definitely established that 

 muscular exercise leads to no increase in the creatinine excretion, al- 

 though it is said that an increase occurs following a tonic contracl 

 of the musides. With regard to the creatinine in the muscles, no definite 

 results indicating thai muscular metabolism chang 3 amount are on 

 record. In the light of the fact already stated regarding' the pres 

 of creatine in other organs than the muscles, it seems probable that the 

 substance has really little to do with muscular contraction h. but 



rather is concerned in some way in the formative metabolism of the cell, 

 with its general growth or maintenance. Indeed, it is a question whether 

 creatine is an actual constituent of the living tissue. It may rat 

 lias 1 n suggested by Polin, be a postmortem product, represented dur- 

 ing life by creatinine. 



