20 



Inside the Living Cell 



phe 



I 

 ser 



I 

 leu 



I 

 tyr 



I 

 glu- 



I 



leu 

 I 

 glu 



I 

 asp< 



I 

 tyr 



I 



cys 



I 

 asp- 



NH2 



NH- 



NH- 



Variants in position B 



Cattle 



ala 

 I 



g'y 

 I 



val 



Pig_ 



thr 



I 



ser 

 I 



ileu 



Sheep 



ala 



I 

 ser 



I 



val 



FIG. 3. The arrangement of the fifty-one amino acids in the molecule of pig 

 insulin (for full names, see Appendix, p. 162). Insulins from other species 

 differ slightly in the short section marked B. asp— NH2 is asparigine and 

 glu — NH2 is glutamine. 



