HUGO THEORELL 



linked cysteine residues, it appeared to us that if the peptide 

 chain has the shape of an a-helix with 3.7 amino acid residues per 

 turn, the cysteine residues would occur at the same side of the 

 helix, perhaps in a favorable position for the thioether bonds. 



When Professor Pauling visited Stockholm to receive his 



(«) 



(b) 



Fig. 1. Hemopeptide of cytochrome c arranged as left-hand 

 a-heUx. When the imidazole is bound to the Fe-atom, the heme is 

 nearly parallel with the axis of the a-helix. (a) Seen perpendicularly 

 to helix axis, (h) Seen parallel with helix axis. a-Carbons of the 

 amino acids numbered as in formula. 



280 



