24 



ring structures similar to the one suggested by Sehmerda 

 may be formed: 



H o OH 



N — C — S — NH3 — CH2OH 



HOCH, — NH3 — S — C — N 

 HO O H 



In the ring structures thus produced we have the same 

 peptide group — CO — NH — as in polypeptides, so that 

 these rings should be capable of further polymerization 

 into double-strand spirals by superposition upon one an- 

 other in the same manner as diketopiperazines. In the 

 double-strand sulphur-peptide spiral the chain-sequence 

 — N — C — S — N — C — S — will occur not only around the 

 rings but also along the length of the spiral, just as in 

 polypeptide spirals the sequence — N — C — C — N — C — C — 

 occurs not only circumferentially but also longitudinally. 



It is believed that under the conditions of Herrera's 

 experiments there will be some transformation similar 

 to the one outlined above, rather than the formation of 

 thiourea resin. Ammonium thiocyanate will not change 

 into thiourea except at elevated temperatures, and the at- 

 tachment of a formaldehyde group to the ammonium 

 nitrogen will probably hinder, rather than help the for- 

 mation of thiourea. On the other hand the hydroxyl 

 group of the formaldehyde residue will be brought into 

 close proximity with the cyanide group (on account of 

 the angular relationships of the valencies) so as to assist 

 in the hydrolysis of the latter. 



In the sulphur-peptide spirals there will be rows of 

 hydroxyl groups along diametrically opposite sides, just 

 as in polypeptide spirals, so that the same type of lattice 

 structure should he produced in both cases. This may be 

 the reason why Herrera has obtained cell-structures and 

 mitotic figures which closely resemble those of living 

 cells. It is possible that sulphur-peptide spirals of this 

 sort may have gradually changed over into ordinary poly- 



