SOME ASPECTS OF BIOCHEMICAL DIVERSITY 301 



normal haemoglobin concentration and at 20° and pH 7-4. It is clear that the 

 haemoglobin of Invertebrates has a distinctly higher affinity for oxygen 

 than human haemoglobin. 



The various haemoglobins also differ with respect to the change in their 

 affinity for oxygen with pH (Bohr effect). Some haemoglobins do not show 

 a Bohr effect; e.g. the haemoglobins of Urechis, of ChiroTiomus larva and 

 vertebrate myoglobin. The haemoglobins of Invertebrates other than those 

 quoted above show only a very feeble effect {Ceriodaphnia laticaudata, 

 Thalassema neptuni, Arenicola marina, Planorbis corneas, Daphnia magna). 

 It is present in a more or less marked degree in the various classes of 

 Vertebrates. 



The haemoglobins also differ from each other in other ways. If for each 

 haemoglobin we measure in angstrom units the span separating the position 

 in the absorption spectra of the a band of oxyhaemoglobin from the a band 

 of carboxyhaemoglobin, we find clear-cut differences. 



In addition, the auto-oxidation of haemoglobin to methaemoglobin is 

 very slow for vertebrate haemoglobin and more rapid with that of Gastro- 

 philus, mammalian myoglobin, and the haemoglobin found in the roots of 

 legumes. 



III. PROTEIN MACROMOLECULES 



We have emphasized the specific character of macromolecules. 

 Even in the arsenal of enzymes common to all cells we find indications of 

 this specificity. The glucose dehydrogenase of vertebrate liver for example, 

 is not inhibited by toluene, whilst that of E. coli is inhibited. Yeast alcohol 

 dehydrogenase is completely inhibited by 0-001 M iodoacetate, whilst even 

 at a concentration of 0-OlM, animal alcohol dehydrogenase remains 

 unaffected. Glutamic acid dehydrogenase of yeast requires TPN as a 

 coenzyme whilst the same enzyme from plants needs DPN. 



When examining the various characteristics of the haemoglobins we 

 noted a number of differences arising from the different properties of the 

 protein moiety. 



Another aspect of diversity in macromolecules is provided by the pro- 

 duction, in animals, of protein molecules circulating in the blood in re- 

 sponse to the injection of various substances. These antibodies are specific 

 for the injection antigens (proteins, polysaccharides, etc.) and react vnth. 

 them to produce a precipitate, or agglutination if the antigen is attached to 

 a cell surface. The antibodies circulating in the blood are usually present in 

 the serum y-globulin fraction. 



The antibody properties of these molecules is due to the special cha- 

 racteristics of a given part of the macromolecule and numerous facts 

 indicate that antibodies of various specificities are very similar to normal 

 globulin except at one very small part of the macromolecule. For example, 



