254 Discussion 



phenolic or alcoholic OH group will account for the 'anomalous' pH variation of the 

 equilibrium constants (George and Lyster, Proc. Nat. Acad. Sci. Wash. 44, 1013, 

 1958). It cannot be a carboxylate group because the pAT is too low. Furthermore, 

 such structures offer the interesting possibility that they remain intact in higher 

 oxidation states, thereby providing an explanation for the different reactivity of 

 peroxidase and catalase toward oxidizing agents. Whatever the true explanation may 

 be, it is clear that any structure suggested for a higher oxidation state that is equally 

 applicable to myoglobin and haemoglobin on the one hand, and to peroxidase and 

 catalase on the other, leaves many questions unanswered. 



Peroxide Compounds of Catalase and Peroxidase 



Lemberg : If there is any change in the porphyrin structure it is more likely to be in Cat. 

 H2O2 1 than in Cat. H2O2 II. As has been pointed out by Chance (/. Biol. C/iem. 179, 

 1331 (1949)), the band in the red part of the spectrum resembling that of verdohaemo- 

 chrome and the low Soret band of the type I compound are indicative of interruption 

 of conjugation in the porphyrin ring; no such evidence is available for the type II 

 compounds of catalase and peroxidase, or for the ferrimyoglobin HjOo compound. 



Williams: Recently Brill and I have been studying the absorption spectrum of compound 

 I formed from ethyl hydrogen peroxide and bacterial catalase. The spectrum we have 

 obtained is somewhat different from that given by Chance. In particular there is 

 evidence for a new absorption band at about 340-360 m/i not present in the spectrum 

 of free catalase, a weak band at 580-600 m/i very like that of the band found in 

 peroxidase compound I, and a lower Soret band. Brill has shown that there is no 

 evidence for free radicals of catalase. We interpret the spectrum, by using several 

 different lines of other relevant evidence, as indicating that compound I is an equi- 

 librium mixture of two components. One component does not have an intact 



porphyrin ring. We believe it to have a methene bridge which is oxidized to .CHOH 



and to have lost an electron from the ring. The second component is a simple ferric 

 complex. In either event the ethyl hydrogen peroxide is a component of the compound 

 I. The two components are also present in peroxidase compound I but the ratio of 

 the two is very different. We will discuss the difference between peroxidase and 

 catalase from the viewpoint of our new evidence. 



The Nature of Catalase-Peroxide Complex I 



By B. Chance (Philadelphia) 



Chance : The nature of catalase complex I is still an enigma in spite of much study. Two 

 views on the structure of this intermediate are possible, viz. that the components of 

 peroxide are: 



(a) a part of complex I ; 



(b) are not a part of complex I. 



Chemical configurations that illustrate these views are: 



CH3OOH + Fe+++-H20^ Fe+++HOOCH3 + HjO (I) 



h 

 CH3OOH + Fe+++ • HgO^ Fe+++0 + CH3OH (2) 



but these are only two of many possibilities, particularly with respect to Eq. (2) 

 where the oxidizing equivalent could alternatively be located in the porphyrin or 

 protein parts of the enzymes. 



Ogura, working in this laboratory, attempted by kinetic methods to determine 

 whether some intermediate form preceded the given complex I, first by optical studies 



