72 BACTERIAL METABOLISM 
which tryptophan is changed to indol by these organisms are as 
follows:^ 
J 
CH2.CHNH2.COOH / \ CH2.CH2.COOH 
+ H2 = I ' 1 "I" ^^3 Indol propionic acid, 
(deamination) \ /\/ + 30 = 
y NH \/ NH 
Tryptophan. Indol propionic acid. 
\ CH2.COOH / \_ 
I I + CO2 + H2O -^ I y 
cm 
+ CO2 
Skatol + 30 
NH \/ NH 
Indol acetic acid. Skatol. 
+ CO2 + H2O 
/ NH 
Indol. 
Indol contains little or no energy for most bacteria, and it is left 
as such in the culture medium or the intestinal tract. Indol is fre- 
quently absorbed from the intestinal tract, but it has little or no 
energy for the human body— it is oxidized in the liver to indoxyl 
and is excreted and appears in the urine as indican. 
O 
/ \__0H / \ O— S- 
-ONa 
NH 
Indoxyl. Indican. 
B. coli, B. proteus and other organisms which "form indol" utilize 
the alanin radical of the tryptophan molecule (alpha amino pro- 
OH OH 
+ H2 = / \ 
+ NH2 
(deamination) ] | Paraoxyphenyl propionic acid 
+ 30 = 
CH2.CHNH2.COOH CH2.CH2.COOH 
Tyrosine. Paraoxyphenyl propionic acid. 
OH OH OH 
I I + CO2 + H2O -* I I 
CO2 I + CO2 + H2O 
Paracresol 
CH2.COOH CW + 30 = 
Paraoxyphenyl Paracresol. Phenol, 
acetic acid. 
> Nencki: Ber. d. deutsch. chem. Gesell., 1875, 8, 722. 
