86 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



LEUCINE AND TYROSINE 



These two substances have been frequently mentioned in the 

 preceding pages, and they are the final cleavage products of proteins 

 which have been longest known. Leucine is usually the most 

 abundant of all the cleavage products (see table on p. 35). 



We have already learnt that they are amino-acids, and that 

 leucine is amino-caproic acid (see p. 31). There are, however, several 

 isomeric amino-caproic acids. It was thought until quite recently 



FIG. 22. Leucine crystals. 



FIG. 23. Tyrosine crystals. 



that leucine was the amino-acid of normal caproic acid, but it has 

 been shown to be a-amino-iso-butyl-acetic acid. The difference in the 

 structure of these two compounds may be represented by the following 

 graphic formulae : 



fCH 3 /CH 3 CH 3 



OH 8 



CH 2 Tso-butyl J CH 



CH 2 a-amino- CH^ 



CH.NH 2 acetic acid CH.NH 2 



COOH I COOH 



Normal 



a-amino-caproic 

 acid 



Tyrosine is a little more complicated, as it is not only an amino-acid, 

 but also contains an aromatic radical (see p. 34). Figs. 22 and 23 

 represent the crystalline forms of leucine and tyrosine. 



