Gene Action and Polypeptides 



413 



a 



• • 



. A i..- ,1 



Hb-S 



.0 



o 









?• 



26 



+ 

 Hb-A 



figure 32-5. The "fingerprints" of hemoglobin obtained after trypsin 



treatment. (Courtesy of V. M. Ingram, from C. Baglioni, Biochim. Bio- 



phys. Acta, 48:392-396, 1961.) 



its peptides. When these and other analyt- 

 ical procedures are carried out, the sequence 

 of all the amino acids in the « A and /3 A 

 chains can be determined (Figure 32-6). 

 Note that the Val in peptide 4 is at the N- 

 terminus of the (3 A chain. 



Persons heterozygous for the gene for 

 sickling have the "sickle cell trait," readily 

 detected when their red blood corpuscles 



are exposed to an oxygen pressure very 

 much lower than normal; persons homozy- 

 gous for this mutant have "sickle cell ane- 

 mia," and their red cells sickle even when 

 the oxygen pressure is not so drastically re- 

 duced. The hemoglobin of both types of 

 persons has been fingerprinted and analyzed 

 for amino acid content. The hemoglobin 

 of the mutant homozygote is identical with 



