202 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



takes place, with formation of a ring compound known as 

 di-aci-piperazin, or di-glycocoU anhydride, 



NH^CHgCOOH-^ NH^CH^COOCaHg-^ 0= C^ )c= 



Glycocoll G-lycocoU 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 

 NHgCHgCO-NHCHgCOOH, the group NH^CHaCO being 

 termed glycyl. The reaction is expressed as follows : — 



CH^-NH 



o=c( c=o + 



Diacipiperazin 



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 : — 



rNH2CH(C^H9)CO[NHCH2CO]3NHCH(C4Hg)CO[NHCH2CO]3l 

 L NHCH(C4Hg)CO[NHCH2CO]8NHCH2COOH J 



It is termed Z-leucyl-triglycyl-Z-leucyl-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. 



