664 METABOLISM 



the growth curves (see page 610) indicate that the organism is capable of 

 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 698). 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 various organs, 

 particularly the kidneys and the liver. 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 oxy- 

 gen, which is best secured by using defibrinated arterialized blood in- 

 stead of artificial serum (Locke's solution). 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 mon- 

 oxide gas through it, no synthesis of hippuric acid will result from per- 

 fusing the blood through the kidney. The kidneys are not the only site 

 of this synthesis, since hippuric acid is still formed after nephrectomy, 

 in both carnivorous and herbivorous animals. It has been isolated from 

 the liver of nephrectomised dogs after injection of glycocoll and benzoic 

 acid (Kingsbury and Bell 60 ) ; and after damaging the liver cells by poi- 

 soning with hydrazin, in dogs, it has been found that the excretion of 

 hippuric acid falls decidedly. Hydrazin does not act on the kidney 

 cells. 61 



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 ;OH+H; HNCH 2 coon). 



Glycocoll may be used for detoxicating other substances than benzoic 

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

 (see page 528) and phenylacetic acid. In birds the benzoic acid be- 

 comes combined with diamino-valerianic acid or orni thine (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 



