

THE METABOLISM OF PROTEIN 665 



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. 



Ethereal Sulphates and Glycuronates. The other substances used for 

 detoxication purposes are sulphuric and glycuronic acids. Phenol, and 

 its derivative cresol, after being absorbed from the intestine, in the 

 contents of which they are produced by the bacterial decomposition of 

 protein (see page 535) become combined in the body, probably in the 

 liver, with sulphuric acid or with glycuronic acid to form the sulphate 

 or glycuronate. The aromatic sulphate further combines with potassium 

 to form the so-called ethereal sulphates, as which the substance is excreted 

 in the urine. A small amount of phenol may however appear in the 

 urine unchanged. As we have already seen, the sources of the phenol 

 in the intestine are tyrosine and phenylalanine (see page 564), and 

 since these amino acids are also present in the tissues, it might be sup- 

 posed that some of the phenol sulphate of potassium present in the 

 urine could come from the tissues. It is usually assumed, however, that 

 derivation from the tissues does not occur. 



Another ethereal sulphate is indoxyl sulphate of potassium, which re- 

 sults from the absorption into the blood of the indole and skatole pro- 

 duced by intestinal putrefaction from tryptophane (see page 536). 

 Immediately after absorption indole is oxidized to indoxyl, which then 

 combines with sulphuric acid and with potassium to form indoxyl sul- 

 phate of potassium, which is the well-known indican of the urine. As 

 in the case of phenol sulphate of potassium, none of the urinary indican 

 seems to come from the normal metabolism (of the tryptophane) of the 

 tissue proteins. It is a much more reliable indicator of the extent of intes- 

 tinal putrefaction than is phenol sulphate of potassium, but it also becomes 

 increased in amount during putrefaction in the body itself, as for example 

 in abscess formation. 



The amount of indican in the urine may be roughly gauged by oxi- 

 dizing the urine by means of hypochlorite and then shaking out with 

 chloroform. If the resulting extract is more than light blue in color, 

 it indicates excessive putrefaction. A negative test does not neces- 

 sarily mean that intestinal putrefaction is absent, but a markedly positive 

 test always indicates that it is occurring. Skatole, the methyl deriva- 

 tive of indole, may undergo similar processes and appear in the urine 

 during excessive intestinal putrefaction. Its presence in the blood some- 

 times confers on the breath a distinctly fecal odor, for this body, as its 

 name indicates, is that to which the odor of the feces is due. 



