IX. GENETICS .\ND HUMAN HEMOGLOBIN CHEMISTRY 



425 



TABLE II (Continued) 



The chemical study of the abnormal hemoglobins by means of the 

 fingerprinting method of analysis was initiated by Ingram (1956). The 

 fingerprints of Hb-A and Hb-S showed that only one peptide in the 

 Hb-S fingerprint occupies a position diff'erent from that in Hb-A finger- 

 prints (see Fig. 2). After tryptic hydrolysis of the human hemoglobins 

 a few large tryptic peptides, accounting for approximately ^ to % of 

 the molecule, are insoluble at neutral pH. These peptides are removed 

 by centrifugation from the tiyptic digest of the human hemoglobins 

 prior to fingerprinting (Ingram, 1958). That portion of the hemoglobins 

 which contains the peptides insoluble at neutral pH has been designated 

 the ''core" of the molecule (Ingram, 1958). The "core" can be examined 

 by fingerprinting after chymotryptic digestion (Hunt and Ingram, 1958a). 

 Hunt and Ingram (1958a) have shown that the fingerprints of the 

 chymotiyptic digest of the Hb-A and Hb-S "cores" are identical. 



The isolation and the analysis of the peptide altered in Hb-S have 

 allowed Ingram (1958) to establish that Hb-S differs from Hb-A by only 

 one amino acid: a valine in Hb-S is substituted for a glutamic acid 

 residue in Hb-A. This fundamental observation which revealed the 

 alteration caused by a mutant gene at the molecular level undoubtedly 

 was a landmark in the history of biology. 



The next abnormal hemoglobin analyzed was Hb-C (Hunt and In- 

 gram, 1958b) ; the same peptide displaced in Hb-S fingerprint is missing 

 in Hb-C fingerprint, while two new peptides appear. The chemical 

 analysis of these peptides (Hunt and Ingram, 1960) showed that the 

 same residue substituted by a valine in Hb-S, namely, a glutamic acid, is 

 replaced in Hb-C by a lysine residue. This new lysine offers a point of 

 attack to trypsin and two peptides appear instead of the altered one in 

 Hb-C fingerprints. 



