202 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



takes place, with formation of a ring compound known as 

 di-aci-piperazin, or di-glycocoll anhydride, 



/CH 2 -NH X 

 NH 2 CH 2 COOH-> NH 2 CH 2 COOC 2 H 5 -> 0- V /C= 



Qlycocoll Glycocoll ethyl ester Diacipiperazin 



On saturating a boiling solution of this compound with 

 gaseous hydrochloric acid, it is split up with formation 

 of the simplest polypeptide, known as glycyl-glycin or 

 NH 2 CH 2 CO-NHCH 2 COOH, the group NH 2 CH 2 CO being 

 termed glycyl. The reaction is expressed as follows : 



Onx 

 ^\ \J=\J ~T boiling ~^V/=V; 



X NH-CH 2 / X NH-CH 2 -C0 2 H 



Diacipiperazin Glycyl-glycin 



It is readily seen that if glycyl-glycin is taken in its turn 

 as a starting point, and a similar set of reactions carried out, 

 further similar complexes of higher molecular weight could be 

 obtained. The most complex polypeptide so far synthesised 

 has the constitution : 



rNH 2 CH(C 4 H 9 )CO[NHCH 2 CO] 3 NHCH(C 4 H 9 )CO[NHCH 2 CO] 3 -i 

 L NHCH(C 4 H 9 )CO[NHCH 2 CO] 8 NHCH 2 COOH 



It is termed Meucyl-triglycyl-Meucyl-triglycyl-Meucyl- 

 octaglycyl glycin. 



It is an octadecapeptide, containing no less than 18 amino- 

 acid residues, giving it a molecular weight of 1213. 



Compounds such as this give the biuret reaction, and are 

 capable of being partially split up by ferments, such as trypsin ; 

 they are in fact nearly akin to peptones, which, as we have 

 seen, are some way on to the complexity of albumin. 



