416 CORRADO BAGLIONI 



urcd l)v alkali (K'liaturatioii. Tlir hiji;li(M- resistance to alkali is in fact 

 the outstaniling characteristic of Hb-F. The reaction which henioglol)in 

 undergoes in alkali is essentially the change of hemoglobin to henio- 

 chromogen (Drabkin and Austin, 1935) ; the rate of this change can be 

 followed quantitatively by spectrophotometry. The methods for the 

 identification and evaluation of Hb-F have been reviewed by White 

 and Beaven (1959). 



The end group analysis of the Hb-F peptide chains has shown the 

 jiresence of two pairs of peptide chains with the N-terminal sequence 

 Val. Leu. and Gly.His.Phe., respectively (Schroeder and Matsuda, 1958). 

 The peptide chains Gly.His.Phe., which were found to be different from 

 the p chains of Hb-A on the basis of their N-terminal sequence, were 

 designated y chains. 



Hunt (1959) has isolated l)y column chromatograi)liy the peptide 

 chains of Hb-F and has examined the pattern of pc])tides after tryptic 

 hydrolysis. The a chains isolated from Hb-A or Hb-F gave identical 

 fingerprints; the fingerprints of the /? and y chains were found to be 

 different. The chemical analysis of the N-terminal sequences of Hb-A 

 and Hb-F and the fingerprinting analysis support the claim that these 

 hemoglobins have a pair of peptide chains in common, the a chains, 

 which are associated with pairs of different chains, /? chains in Hb-A 

 and y chains in Hb-F. A sequence of the a chain of Hb-F has been 

 reported by Schroeder et al. (1961) ; this sequence is in agreement with 

 the sequence of the a chain of Hb-A reported by Konigsberg et al. 

 (1961) and by Braunitzer et nl. (1961b). Schroeder et al. (1961, 1962) 

 have determined the sequence of the y chain of Hb-F. This sequence 

 is reported in Fig. 4 together with the sequence of the /? chain of Hb-A. 

 Genetic evidence showing that the a chains of Hb-F and the a chains 

 of Hb-A are under the control of the same gene has been accumulating 

 in the past few years (Baglioni et al, 1961; IVIinnich et al., 1962), so 

 that there is little doubt today that these peptide chains are chemically 

 identical (see Section IV,E). 



Since Hb-A and Hb-F have in common the same a chains, the higher 

 alkali resistance of Hb-F has been attributed to a property of the y 

 chains. The denaturation of Hb-F at alkaline pH's follows, however, 

 a first-order kinetics, with no break in the linear plot corresponding to 

 the presence of a resistant portion of the molecule (Charlwood et al., 

 1960). Hb-A is known to dissociate at pH 11.0 into symmetric subunits 

 (see Section IV,D) of molecular weight approximately half that of 

 hemoglobin ('Hasserodt and Vinograd, 1959). Al)ove pH 11.0. Hb-A dis- 

 sociates into subunits of smaller molecular weight, pi'esuniably into 



