THE METABOLISM OF PROTEIN 631 



producing new glycocoll for itself, and it is interesting to consider how 

 this glycocoll may be derived. A very probable source is by synthesis 

 between ammonia and glyoxylic acid (CHO. COOH). That glyoxylic acid 

 or its aldehyde,, glyoxal, is readily produced during metabolism from car- 

 bohydrates and that ammonia is always available would seem to lend 

 some support to this view (see page 665), The synthesis of glycocoll 

 from glyoxal and ammonia occurs thus: 



H.COCHO + NH 3 CH,NH 2 COOH. 



(glyoxal) (glycocoll) 



The linking up of glycocoll with benzoic acid occurs in the kidney. 

 If the kidney is removed from the circulation in the majority of animals 

 that produce hippuric acid in large amount the rabbit being an excep- 

 tion no hippuric acid will accumulate in the blood. On the other hand, 

 an isolated perfused preparation of the kidney produces hippuric acid 

 provided benzoic acid is added to the perfusion fluid, and the latter also 

 contains an abundance of oxygen, which is best secured by using de- 

 fibrinated arterialized blood instead of artificial serum (Locke's solu- 

 tion). The necessity of a plentiful supply of oxygen is further shown 

 by the fact that, if the hemoglobin of the blood is rendered incapable 

 of carrying 2 by bubbling carbon monoxide gas through it, no synthe- 

 sis of hippuric acid will result from perfusing the blood through the 

 kidney. The actual chemical process by which the synthesis occurs (de- 

 hydration) is similar to that by which polypeptides are formed by the 

 union of amino acids, or creatinine from creatine. 



(C 6 H 5 CO j OH + H| HNCH 2 COOH). 



Glycocoll may be used for detoxicating other substances than benzoic 

 acid, particularly cholic acid, forming the glycocholic acid of the bile 

 (see page 494) and phenylacetic acid. In birds the benzoic acid be- 

 comes combined with diamino-valerianic acid or ornithine (NH 2 - CH 2 - 

 CH 2 - CH 2 - CH - NH 2 - COOH) in place of glycocoll, so that in the urine 

 of these animals in place of hippuric acid a compound called ornithuric 

 acid occurs. 



It is of importance to point out here that this pairing of aromatic toxic 

 substances with certain of the metabolic products of the organism has 

 frequently been found an excellent experimental method for demon- 

 strating the presence of intermediary metabolic substances that other- 

 wise would not have appeared in the excreta. These substances are 

 thus diverted from their normal course in metabolism so as to form 

 neutralization or detoxication compounds. Glycuronic acid is an example. 



