E. M. JOPE 



tyrosine/tryptophan ratios of about 3:1, agreeing more closely with 

 some of Block's more recent chemical analyses 32 and also more closely 

 with the usual haemoglobin tyrosine/tryptophan ratio. It would have 

 been difficult to see how the tryptophan could suddenly rise in the 

 preparation of globin from haemoglobin unless the 67,000 unit split 

 into two unequal parts and one only remained in solution. The 

 haem group absorption unfortunately makes such a spectrophoto- 

 metric analysis difficult on haemoglobins themselves. 



The spectral absorption of tryptophan shows a prominent peak at 

 288 my.. In some polypeptides, such as gramicidin, this band appears 

 also at 288 my., but in most tryptophan-containing proteins, it appears 

 at a considerably longer wavelength, 291 my. in most cases. The 

 cause and significance of this wavelength shift will be discussed in 

 detail elsewhere by Dr Holiday and myself. Three interesting ex- 

 ceptions concern us here — human foetal haemoglobin, many mam- 

 malian muscle haemoglobins and preparations of globins from 

 mammalian red cell haemoglobins. In human foetal haemoglobin 

 this band appears at 289-8 m\x and it is particularly remarkable that 

 other mammalian foetal haemoglobins, sheep and rat, show this 

 band in the usual protein position of 291-0 m[i (Table II). 



Table II 

 Tryptophan absorption band wavelengths in haemoglobins (in my.) 



216 



