THRE CHEMISTRY OFTHE ‘PROTEINS III 
octaglycylglycine. This decapeptide, on combination with 
bromisocapronyl diglycylglycine, and subsequent replacement 
of Br by NH,, yields the tetradecapeptide 
NH,CH(C,H,)CO . [NHCH,CO}],. NHCH(C,H,)CO.[NHCH,.CO],. 
NHCH,COOH, 
and a repetition of the process of combining with bromisocap- 
ronyldiglycylglycine gives the octadecapeptide 
NH.CH(C,H,)CO .[NHCH,CO};. NHCH(C,H,)CO . [NHCH,CO}. 
NHCH(C,H,)CO .[NHCH,CO},. NHCH,COOH. 
Many technical difficulties had to be surmounted in its 
preparation which were successfully overcome ; e.g. prevention 
of frothing by shaking up with glass beads, etc. 
The molecular weight of this compound is 1213. It far 
exceeds that of the fats, of which tristearin has the molecular 
weight 891, and it belongs to the most complicated combinations 
ever obtained synthetically without our losing the knowledge of 
its constitution. If, in place of the glycine residues, it contained 
tyrosine, phenylalanine, or leucine residues, its molecular 
weight would be increased two- to three-fold, 7e. to values 
taken as the normal for many natural proteins. The values of 
12,000—15,000 for other proteins, according to Fischer, are 
uncertain, as we have no guarantee of the purity of these 
natural substances. 
Up to the present time nearly one hundred different poly- 
peptides have been prepared. Their structure is derived directly 
from their synthesis, and they are generally represented as in 
the formule given in the above equations. Other structures are 
also possible; indications of these have been observed in their 
study, and they are at present only of theoretical interest. 
The configuration of the polypeptides is of extreme im- 
portance, for, with the exception of glycine, all the amino acids 
contain an asymmetric carbon atom. According to van’t Hoff’s 
formula, 2", the number of isomers possible when two amino 
acids are combined together is four, namely, the dd, ll, dl, ld 
forms ; and two racemic forms—dd, I] and dl, ld—can be obtained 
from these. With more amino acids coupled together the 
complications are still greater, and their separation well-nigh 
impossible. Fortunately, these conditions do not seem to be 
present in the protein molecule, since the amino acids as they 
result on hydrolysis are optically active and! hence exist in 
