THE BIOCHEMISTKY OF THE THYKOID GLAND 257 



Thyroxin, as represented by formula (i) is a white, highly crystalliz- 

 able substance (needles), odorless, and tasteless. It exists in this keto form 

 in acid solution. It is insoluble in organic solvents except those strongly 

 acidic or basic; it is soluble in alcohol in the presence of a mineral 



II 



I H 



-X 



C CH 2 CH 2 COOH \C C C CH 2 CH 2 COOH 



OH 



i. Keto form. 



I/x /- \ 



C NH 2 

 H 



^OOH 





C C CH 2 CH 2 COOH 



OH 



iii. Open ring form. 

 H 



\ 



iv. Ammo-hydrate. 





C C CH 2 CH(NH 2 ) COOH 



C 



H-i 



v. Tryptophan. 



acid or an alkali. It is stable towards heat (m.p. about 250 C.), its 

 molecular weight is 585, and the empirical formula CnH^OgNIs. It is 

 amphoteric. Through the presence of the imino group it easily gives rise 

 to salts: sulphate, hydrochlorid, a ureid (with HCNO), an acetyl deriva- 

 tive (with acetic anhydrid). These are all crystalline compounds. It 

 yields crystalline mono-salts (Na, K, NH 4 ) and di-salts (Na, K, NH 4 , Ba, 



