502 



DIGESTION 



Putrefaction of tryptophane is probably preceded by dcamidization 



en 



//\ 

 nc c- 



-C'—L'il .('11X11 ,('()( )H 



IIC c- 



I I! li 



BC C CH 



\/\/ 



CH Ml 



(tryptophane) 



<'ll 



//\ 

 lie C C— CH...COOH 



(NH a ) 



lie < ' CH 



VH NH 



(indole-acetic acid) 



(C0 2 + HX>) 



C— CH 2 CH 2 .COOB 



HC C CH (CO. + Hp) 



CH NH 



(indole-propionic acid ) 

 CH CH 



//\ //\ 

 IK' C CH IK' C C— CH 3 



I II II I II II 



HC C CH IK' C C 



\/\/ \/\/ 



CH NH (+CH 3 ) CH NH 



. (indole) (skatole) 



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

 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, phenolethylamine; from histidine, 

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

 imidazylethylamine, and so on. The process of formation is illustrated 

 in the accompanying formula?: 



1. CH 3 .CH(NH 2 ).COOH = C0 2 + CH 3 .CH 2 (NH 2 ) 



Alanine Ethylamine 



2. C 6 H,(OH).CH 2 .CH(NH 2 ).COOH = C0 2 + C 6 H 4 (OH).CH,.CH 2 .NH 2 



Tyrosine Phenvlethvl amine 



3. C,X 2 H,.CH 2 .CH(NH,).COOH = C0 2 + C 3 H 3 N ;i . CH 2 '.CH 2 .NH 2 



Histidine. Imidazyletliylamine. 



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 737), and may be described as a methylated ethyla- 

 mine derivative of tyrosine. 



Phenylaeetic 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 arc developed very largely upon the vascular 

 system ; histamine, for example, produces marked vasodilatation and 

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



