1 16 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



Sorerisen suggests that the same reactions might be employed for 

 the synthesis of aspartic acid and of glutamic acid, in the case of the 

 former by condensing the sodium phthalimidomalonic ester with chlor- 

 acetic ester, and in that of the latter with yS-chloropropionic ester, 

 Cl . CH 2 . CH 2 . COOC 2 H 5 . In view of our having only one synthesis 

 of each of these two amino acids, and that these syntheses are somewhat 

 arduous, Sorensen's suggestion might with advantage be carried out 



Glutamic acid, as also its salts and esters, is very easily converted, 

 when heated, into its anhydride, pyrrolidone carboxylic acid : 



COOH 



CH 2 CH 2 CH 2 



CH 2 = H 2 O + CO CH . COOH 



CH.NH 2 jfo 



COOH 



and vice versa^ pyrrolidone carboxylic acid is easily reconverted into 

 glutamic acid by hydrolysis with acids or alkalies. 



On account of this ready interconversion of the one compound into 

 the other there is the possibility that pyrrolidone carboxylic acid is pre- 

 sent in the protein molecule in the place of glutamic acid, or at any rate in 

 place of part of the glutamic acid. 



Though this possibility does not seem likely in the case of those 

 proteins examined by Osborne, Leavenworth and Brautlecht, who found 

 that the amount of amide nitrogen corresponded very closely with the 

 amount of dibasic monamino acid, yet in other proteins pyrrolidone 

 carboxylic acid may be present. The method of hydrolysis, which 

 would in any case yield glutamic acid, gives no clue, but a clue may be 

 obtained if pyrrolidone carboxylic acid is formed by the action of 

 enzymes. This question is under investigation by Abderhalden and 

 Kautzsch, who are devising a method for their separation. Glutamic 

 acid differs from pyrrolidone carboxylic acid in forming a carbamino 

 acid. (See Part II.) 



The easy formation of a pyrrole ring compound from glutamic acid, 

 which occurs so widely in nature, suggests that the pyrrole ring in 

 chlorophyll and haemoglobin may arise from this compound. The 

 reduction to prolirie has been effected by Fischer and Boehner. 



