PROTEIN STRUCTURE 



hydryl or disulfide groups. Limited knowledge of some sequences 

 in the peptide chains in other proteins has been achieved. The 

 difficulties of sequence determination are formidable, and 

 become increasingly so as the length of the chain increases. 

 Even for molecules as relatively simple as lysozyme or ribo- 

 nuclease, the chain length is of the order of 1 30 residues, and the 

 problem is far more complex than in the case of insulin. How- 

 ever, the pace of progress is so rapid that a complete structure 

 determination, for these relatively small proteins, may be a 

 matter of only two or three years. 



We tabulate some of the most important sequences already 

 determined, and invite the reader to contemplate them, to see 

 whether he can make some attempt to read the riddles with 

 which they confront him. 



NH, S 



Beef Insulin, 

 A Chain 



Gly. lieu. Val.Glu.Glu.Cy.Cy. Ala. Ser.VaL.Cy.Ser. 

 1 2 3 4 5 6 7 8 9 10 11 12 



Beef Insulin, 

 B Chain 



NH, 



NH, 



S NH, 



Leu . Tyr . Glu . Leu . Glu . Asp . Tyr . Cy . Asp . 

 13 14 15 16 17 18 19 20 21 



NH2 NH2 



I 



Phe . Val . Asp . Glu . His . Leu . Cy . Gly . Ser . His . Leu . Val . 

 1 2 3 4 5 6 7 8 9 10 11 12 



Glu. Ala. Leu. Tyr. Leu. Val. Cy. Gly. Glu. Arg. Gly. . . 

 13 14 15 16 17 18 19 20 21 22 23 



Phe . Phe . Tyr . Thr . Pro . Lvs . Ala 



24 25 26 27 28 29 30 



Pig Insulin Sequence same as in beef insulin except for residues 8, 9, 



and 10 in the A chain, for which the sequence is Thr.- 



Ser.Ileu. 

 Sheep Insulin Sequence same as in beef insulin except for residues 8, 9, 



and 10 in the A chain, for which the sequence is Ala.- 



Gly.Val. 



383 



