OXIDASES, PEROXIDASES, AND CATALASE 91 



to Dr. Gorin, one would expect, if Keilin's theory were correct, that 

 the reduced form of catalase would accumulate in contact with 

 hydrogen peroxide and in the absence of air. The spectrum of the 

 ferro form of the enzyme, as obtained by treatment with sodium 

 hydrosulfite in the presence of hydrogen sulfide and subsequent 

 removal of the latter, has recently been described by Zeile et al. 

 (87). No spectral change, on the other hand, has as yet been reported 

 for a mixture of catalase and hydrogen peroxide under nitrogen. 

 Attempts to "catch" those ferro-catalase molecules, which might 

 possibly be formed as intermediate products during the catalase- 

 hydrogen peroxide reaction, with the aid of carbon monoxide have 

 been unsuccessful (61). The story of the eflFect of carbon monoxide 

 on catalase under various conditions is just as controversial as the 

 subject of its reaction mechanism (cf. 11, 61, 27). It may suffice 

 here to mention Keihn and Hartree's observations (27) that purified 

 carbon monoxide, in the absence of oxygen, exerts an inhibiting 

 eflFect on the enzyme which is not reheved by light, whereas certain 

 catalase preparations may be made sensitive to carbon monoxide 

 inhibition in the presence of oxygen by adding traces of azide, 

 cysteine, and glutathione. This eflFect of carbon monoxide is stated 

 to be completely relieved in a reversible manner by light. The 

 mechanism of this "sensitization" and the reason why crude enzyme 

 preparations are more readily inhibited by carbon monoxide than 

 chemically purified fractions are still obscure. It would seem that, for 

 the present at least, the observations made with the use of carbon 

 monoxide aflFord no basis for supporting or rejecting Keilin and 

 Hartree's reaction schema. The same is true, in the writer's opinion, 

 of the spectroscopic observations made by Keihn and Hartree (26) 

 on catalase solutions containing sodium azide or hydroxylamine in 

 addition to hydrogen peroxide. 



Let us now turn to the theoretical objections raised against Keilin 

 and Hartree's schema. As Weiss and Weil-Malherbe (80) point out, 

 an exclusive reoxidation of ferro-catalase by oxygen would in eflFect 

 prevent a decomposition of the hydrogen peroxide. For unless a 

 radical chain mechanism is postulated, the oxygen formed by the 

 reduction of the ferri form of the enzyme by hydrogen peroxide 

 (Step I, p. 90) is quantitatively used up again for the reoxidation 

 of a stoichiometric amount of the ferrous form with a simultaneous 

 reduction of the oxygen to hydrogen peroxide. To avoid this diffi- 

 culty, Keilin and Hartree formulate the oxidation reaction (Step II, 

 p. 90) in such a way that the reduction of oxygen to water does 



