52 The Nature of Biological Diversity 



geous mutation operating through a further mutation to a disadvan- 

 tageous outcome. 



In what has just heen said it would appear that the invention of 

 hemoglohin is certainly a gain event on the whole, for with its ac- 

 quisition many animals were enabled to penetrate into regions which 

 they could not otherwise have occupied, and were assured of a more 

 abundant supply of . oxygen and a consequently greater potential 

 activity, even in their normal habitats. Subsequent mutations in the 

 human race — and there surely must be others elsewhere among ani- 

 mals — seem to have had only indifferent consequences in some cases 

 (hemoglobin C), while others have been well on the way toward 

 being lethal (hemoglobin S) . 



Table 3. Chemical differences between normal and abnormal hemoglobins 



Hemoglobin Structural characteristics Chain in which structures occur 



A Val.hisJeu.thr.pro.gZu.glu.lys. N-terminal sequence of /3 chain 



S Val.his.leu.thr.pro.faZ.glu.lys. N-terminal sequence of /3 chain 



C Val.his.leu.thr.pro.Zys.glu.lys. N-terminal sequence of /3 chain 



G# Val.his.leu.thr.pro.glu.Zys.lys. N-terminal sequence of /3 chain 



E Gly.gly.Zys.ala.leu.gly. 



(Lys. replaces glu. of Hb-A) 

 I Try.gly.nsp.val.gly. 



(Asp. replaces lys. of Hb-A) 



Peptide in j3 chain 

 Peptide in a chain 



source: Prankerd (1961). 



Any discussion of the species-specificity of proteins leads one into 

 deep waters, for relatively little is known even today about the de- 

 tailed chemical structure of these materials. However, insulin is a 

 protein of fairly small molecular size and of which the structure is 

 precisely known through the brilliant work of Sanger and his co- 

 workers (Brown, Sanger, and Kitai, 1955; Harris, Sanger, and Naugh- 

 ton, 1956). They have shown that insulin is species-specific and have 

 discovered the precise nature of the differences between a number of 

 different insulins. Some of their results are summarized in Table 4. 

 All this demonstrates that it is possible to have a number of substances 

 which, though chemically different, nevertheless possess identical 

 physiological or pharmacological activity. 



Belatively little is known about the comparative side of enzymol- 

 ogy, though important advances have been achieved in elucidating 

 the structure of ribonuclease (Anfinsen & White, 1961). An interest- 

 ing point of a somewhat different kind is that, as is now well known, 



