30 Spirazines 



acid and arginine obtained therefrom upon 

 hydrolysis. 



Sulphur occurs in the molecular structures of 

 nearly all proteins, but is seldom present in 

 amounts greater than two or three percent. Al- 

 though several different sulphur compounds have 

 been obtained from proteins upon hydrolysis, yet 

 they all have their sulphur in chemical combina- 

 tion with the beta carbon atoms of alpha amino 

 acids and appear to be merely ditf erent cleavage 

 products of the same original structures. The 

 principal sulphur-containing cleavage product is 

 cystine, which contains a pair of sulphur atoms 

 between two alpha amino acid groups. If we 

 assume that all alpha amino acid groups were 

 derived from spirazines, then we shall have to 

 conclude that sulphur takes the place of the 

 gamma carbon atoms at double junctions for con- 

 necting two adjacent spirazines. It probably 

 occurs only at the surfaces and not generally 

 throughout the interior molecular structures be- 

 cause the interior structures would require triple 

 rather than double junctions, and furthermore 

 the amount of sulphur in proteins is not sufficient 

 for general distribution. 



If we assume a sulphur content of 2.5 percent, 

 which is more than most proteins contain, then 

 there would be about one cystine molecule or two 



