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291 



White 

 Chain 



Black 

 Chain 



(d) 



Figure II (cont.). Perutz's model of hemoglobin. The white 

 units are an identical pair as are the two black units. Each 

 unit is very similar to myoglobin in the shape of the peptide 

 chain, (c) Hemoglobin model. The heme groups are indi- 

 cated by grey disks, (d) Chain configuration in the two 

 sub-units facing the observer. The other two chains are 

 produced by the operation of the dyad axis. After M. F. 

 Perutz, et al., "Structure of Hemoglobin," Nature 185: 416 

 (1960). 



