38 The Nature of Biological Diversity 



B* 



phate in present-day organisms and perhaps to the appearance of 

 ATP in primitive organisms as well. 



Figure 12 shows that, starting with the primitive function of iron 

 for the decomposition of hydrogen peroxide, which will he formed in 

 the seas either hy ultraviolet radiation or hy K 40 radiation, the iron 

 catalysis can he improved hy a factor of 1,000 if it is built into a 

 porphyrin. If we now- transform this iron further by encasing the 

 heme into a folded protein and make the molecule of catalase, the 

 catalytic function is improved hy another factor of 10 million for this 

 particular peroxide decomposition reaction. 35 



This fact is of great importance because I believe that peroxide 

 appeared in the primitive seas of the earth at the very earliest stages 

 as a result of both the ultraviolet radiation at the top of the atmos- 

 phere and of the potassium-40 radioactivity in the earth's crust. This 

 peroxide can now serve as an evolutionary selection pressure 38 to 

 improve the catalytic function of iron from the bare iron to the iron 

 heme to the iron heme-protein combination. 



The way in which this can occur is shown by having a look at the 

 way in which hemes are synthesized by modern living organisms 

 (Fig. 13). We start with succinic acid and glycine, which were made 

 by random synthesis from the primitive earth's atmosphere, and by 

 combining these two substances, we make the alpha-amino-beta-keto- 

 adipic acid which then decarboxylates to give the delta-amino-levu- 

 linic acid, two of which can combine to form the heterocyclic pyrrole 

 ring. Then there follows a series of oxidation and condensation steps 

 to give rise to the tetrapyrrole ring. 39 This reaction is a spontaneous 

 one which involves a number of oxidation steps, several of which are 

 almost certainly catalyzed by iron. The oxidation is achieved either 

 by oxygen or peroxide under the influence of iron and presumably 

 better achieved by iron in a porphyrin than by bare iron. Therefore, 

 once the porphyrin is formed, more of it will be formed because of this 

 autocatalytic self-selection mechanism. 4 ' 7 



Pyrophosphate formation 



This idea is important because the mechanism of the formation of 

 pyrophosphate seems to involve the oxidation of iron. In the last 

 few months, we have been able to demonstrate that one can generate 

 pyrophosphate in aqueous media by simply allowing hydrogen perox- 

 ide to oxidize ferrous iron in the presence of orthophosphate. 40 In 



