THE PROTEINS AND THEIE METABOLISM 111 



It does not give rise to acetone bodies. Its conversion into glucose in 

 all probability is also through a malic acid stage. 



COOH COOH COo 



CH 2 CH 2 CH 3 



I 1 I 



CHOH > CHOH > CHOH - Glucose 



CHNH 2 COOH COOH 



COOH CO 2 



|3-hydroxyglutamic Malic Lactic 



acid acid acid 



Serin is converted into glucose, in all probability quantitatively. After 

 deamination it may give rise to glyceric acid, which is convertible into glu- 

 cose. (Dakin, Ringer and Lusk.) 



CH 2 OH CH 2 OH 



CHNH, Deamination CHOH > Glucose 



COOH COOH 



Serin Glyceric acid 



Cystin in the body is broken up into two molecules of cystein. 

 CH 2 S - - S CH, CH,SH 



CHNH 2 CHNH 2 - -*2 CHNH 2 



COOH COOH COOH 



Cystin Cystein 



Cystein may undergo deamination and desulphurization yielding a 



three carbon compound which is completely converted into glucose (Dakin). 



The intermediary products are, in all probability, similar to those of serin. 



Cystein to a small extent may also undergo decarboxylation, giving 



rise to thioethylamin, which on oxidation gives rise to taurin. 



CH 2 SH CH,SH CH 2 SO 2 OH 



Decarboxylation | Oxidation 

 CHNH 2 - > CH 2 NH 2 - -> CH 2 NH 2 



COOH CO 2 



Cystein Thioethylamin Taurin 



This taurin is used by the liver cells to combine it with cholic acid, form- 

 ing taurocholic acid, which is one of the bile salts. This is therefore the 



