536 



DIGESTION 



Putrefaction of tryptophane is probably preceded by deamidization : 



CH 



C C CH 2 CH 2 .COOH 



(NH,) 



CH 

 H/V 



I I 



HC C CH 



\X\X 

 CH NH 



(indole-propionic acid) 

 CH 



(C(X + H 2 0) 



-CH 



HC 



(+CH 3 ) 



\/ \/ 



CH NH 



(CO 2 +H.,0) HC C CH 



\X\X 

 CH NH 

 (indole-acetic acid) (indole) (skatole) 



If, however, the carboxylase bacteria remove the carboxyl group be- 

 fore the amino group has been removed, highly toxic substances called 

 amines are produced. They are the so-called ptomaines. From alanine, 

 ethylamine is formed; from tyrosine, phenoleTTryTamine ; from histidine, 

 which it will be remembered is an important protein building-stone, 

 histamine, (imidazyl ethylamine) and so on. The process of formation is 

 illustrated in the accompanying formulae: 



1. CH 3 .CH(NH 2 ).COOH CO 2 -f- CH 3 .CH 2 (NH,) 



Alanine Ethylamine 



2. C 6 H,(OH).CH,.CH(NH 2 ).COOH CO 2 -f C 6 H 4 (OH) .CH,.CH 2 .NH 2 



Tyrosine Phenylethylamine 



3. C s N,H 3 .CH 2 .CH(NH 2 ).COOHz=CO, + C 3 H 3 N 2 . CH 2 .CH 2 .NH, 



Histidine. Histamine. 



Similar substances are very common in the metabolic products of 

 plants; for example, they constitute the active principle of ergot. They 

 are also no doubt produced in the tissues of mammals, imidazylethyla- 

 mine, commonly called histamine, being thus produced, as well as the 

 closely related epinephrine, which is the active principle of the supra- 

 renal gland (see page 773), and may be described as a methylated ethyla- 

 mine derivative of tyrosine. 



Phenylacetic acid produced by a similar process from tyrosine may 

 be excreted in the urine, where it forms the mother substance of homo- 

 gentisic acid, to which the dark brown color of the urine in alkaptonuria 

 is due. 



The great importance attached to these decomposition products of proteins 

 depends on the fact that they have powerful pharmacological actions. These 

 actions are developed very largely upon the vascular system; histamine, 

 (pages 253 and 307) for example, produces marked vasodilatation and 

 lowers the coagulability of the blood, whereas other substances of the 

 same class, like epinephrine, have the property of raising the blood pres- 

 sure. In larger doses, serious nervous symptoms and a condition of pro- 



