474 G ASTRO-INTESTINAL "AUTOINTOXICATION" 



ALKAPTONURIA 1 



Alkaptonuria may be appropriately considered in this connec- 

 tion, since it depends on an abnormal metabolism of the aromatic 

 groups, tyrosin and phenylalanin, which are, partly at least, split 

 out of the proteid molecule in the intestine. This condition is 

 characterized by the tendency of the urine to turn dark on 

 exposure to air, due to the presence in it of two aromatic sub- 

 stances, homogentisic and uroleucic acids. 2 It is of rare occur- 

 rence, persists throughout life with but little apparent effect 

 upon the health of the individual, and is often hereditary, being 

 grouped by Garrod 3 along with cystinuria and albinism as a 

 " chemical malformation " of hereditary origin. The relation 

 of these aromatic bodies to the aromatic constituents of the 

 proteids is best shown by comparing their structural formulae : 4 



Phenylalanin, <CH 2 - CHNH 2 - COOH. 



Tyrosin, HO-/^)cH 3 -CHNH 2 -COOH. 



_OH 

 Uroleucic acid, / \CH 2 CHOH COOH. 



OH 

 Homogentisic acid, CH 2 COOH. 



Apparently the condition depends upon an abnormality in the 

 intermediary metabolism, and not upon an abnormal formation 

 of homogentisic acid through intestinal putrefaction, as was at 

 first believed. This abnormality consists not in the excessive 

 formation of homogentisic and uroleucic acids, but in a lack of 

 ability on the part of the alkaptonuric individual to split open 



byFalta, Biochem. Centralblatt, 1904 (3), 174, and 

 )4 (81), 231. Also see Abderhalden, " Lehrbuch der 



1 Re'sume' and literature 

 Deut. Arch. klin. Med., 1904" 

 Physiologischen Chemie," Berlin,' 1906, pp. 294-298. 



2 It should be mentioned that hydrochwon, when present in the urine (usually 

 after ingestion of large quantities of phenol), may also turn dark on exposure 

 to air ; and melanin may be excreted as a chromogen which turns dark on 

 exposure, by patients with melanotic tumors orochronosis (q. v.). 



~ z Lancet, 1902 (ii), 1616. 



4 Concerning the formation of homogentisic acid from tyrosin in plant 

 tissues, see Schulze and Castoro, Zeit. physiol. Chem., 1906 (48), 396. 



