394 VIII. HEMATIN ENZYMES, I. CYTOCHROME SYSTEM 



In conformity with the hypothesis that Fe^^02 acts as an oxidative 

 catalyst we can write this: 



Fe*^02 (H2X) + Fe'^ ^ Fe'^ (OH)X + Fe'^ (OH) (3) 



It will be shown in Chapter X that a similar reaction between Fe* O2 

 and H2X may occur when oxyhemoglobin reacts with hydrogen 

 donors, the intermediate stage being the formation of an Fe' 

 hydrogen peroxide compound. In these cases, the hydrogen donor is 

 another molecule perhaps bound to hemoglobin; in the present 

 instance the hydrogen donor must be a group in the globin part of 

 hemoglobin (or myohemoglobin) itself. As early as 1924 Baudisch 

 and Welo (192) discussed the possibility of an Fe02 compound acting 

 as hydrogen acceptor. This hypothesis brings into close relationship 

 the formation of hem?'globin from hemoglobin by the action of reduc- 

 ing substances in the presence of oxygen and that by autoxidation. 

 We have seen above that Neill had been impressed by the similarity 

 between these reactions. If equation 3 represents the autoxidation of 

 myohemoglobin one should expect to find the latter dimolecular with 

 regard to total myohemoglobin concentration ; this has been assumed 

 to be the case by Brooks (S^O), but still requires experimental 

 verification. 



Equation 2 postulates the existence in the globin of hydrogen 

 donor groups able to supply four atoms of hydrogen per Hb4 molecule, 

 while we have seen above that so far only two such groups have been 

 discovered. The formula is, however, well supported by the obser- 

 vation that acid or pyridine, on denaturing oxyhemoglobin, liberate 

 only two of the four oxygen molecules, a third one being evidently 

 required for the oxidation of four iron equivalents, while the fourth 

 must be used in oxidizing two H2X groups of the globin (c/. next 

 section). 



Hb4(02)4 ^ Hb4* + 4 O2 



Hb4* + O2 + 2 H2O ^ Hb4*(OH)4 



2 H2X + O2 ^ 2 H2Q + 2 X 



Hb4(02)4(H2X)2 -> Hb4*(OH)4(X)2 + 2 O2 



The asterisk represents denaturation of the globin. 



This working hypothesis is amenable to experimental verification. 

 It is generally assumed that the preparation of hemiglobin by autoxi- 

 dation is particularly mild. Our hypothesis demands that the globin 

 of hemiglobin produced by autoxidation should differ from that of 



