OXIDASES, PEROXIDASES, AND CATALASE 85 



rapid reactions affords further proof of the existence of enzyme- 

 substrate complexes as intermediates in the peroxidate catalysis. 

 The nature of the ternary complexes formed by catalase, hydrogen 

 peroxide, and some inhibitors is not yet clear. They may represent 

 ternary complexes between enzyme, substrate, and inhibitor, but 

 they may also be binary enzyme-substrate compounds the lifetime 

 of which is prolonged by the presence of the inhibitors. The inter- 

 pretation of the phenomena observed in the foregoing enzyme 

 reactions is reinforced considerably by observations made on such 

 closely related, non-enzymatic models as the methemoglobin- 

 hydrogen peroxide (21) and methemoglobin-ethyl hydrogen per- 

 oxide (58) complexes and the hemin-hydrogen peroxide intermedi- 

 ate (22). If we go back a little, we find that in 1905 Spitalsky 

 observed analogous phenomena in the chromic acid-hydrogen per- 

 oxide catalysis. It is safe to conclude that similar inteimediates arise 

 in all hemin-catalyzed reactions even if they cannot yet be demon- 

 strated experimentally. The writer has just been informed by 

 Professor Hogness that cytochrome peroxidase, too, forms a typical 

 enzyme-substrate complex with hydrogen peroxide. 



The oxidation of ferrous iron to ferric iron by oxygen is usually 

 regarded as a process fundamentally different from the oxygenation 

 of hemoglobin. However, it would simplify matters a good deal if 

 both types of reactions could be brought to a common denominator. 

 In agreement with Haber* and Warburg the reviewer believes that 

 this common link is that in the ferrous-ferric transformation by 

 molecular oxygen an oxygenated intermediate of a structure analo- 

 gous to oxyhemoglobin is interposed (see Oppenheimer and Stern 

 (49), pp. 14ff.): Fe^+ + O, -» Fe^O^ -» Fe^^\ 



The reasons for this hypothesis are, first, that molecular oxygen, 

 despite its high potential ( + 0.8 volt), appears to be too sluggish an 

 oxidant to react rapidly with ferrous iron without prior activation. 

 It is logical to assume that the hydrogen peroxide, formed as a result 

 of the oxidation of the ferrous iron, arises by interaction of the 

 ferrous-oxygen intermediate with water molecules or hydrogen ions. 

 Secondly, the well-known competition of molecular oxygen and 

 carbon monoxide for the ferrous fomi of the respiratory ferment, 

 which is governed by Warburg's distribution equations, would be 



* This concept appears applicable even to the simplest reactions in the gas 

 phase. Thus Haber and Sachsse (16), on the basis of kinetics experiments, 

 conclude tliat during the reaction of sodium vapor with oxygen one sodium 

 atom combines with one oxygen molecule. 



