The Isolation, Purification and Properties of Haemin a 



Table 1. Comparison of extinction coefficients 

 OF CO compounds 



333 



of /? bands in some action spectra have both been commented upon (Dixon and Webb, 

 Enzymes, Academic Press Inc., 1958, p. 423). The third point is that the molecular 

 extinction coefficients of the CO compound of cytochrome a^ are known from photo- 

 dissociation kinetics to a reasonable accuracy to be 12cm~^ x mM~^ for the a band 

 and 115 for the Soret band. These data, when compared with haem a-CO data, 

 show reasonable similarities. 



Cryptohaem a 



Morell: The origin of cryptohaem is of some interest. In contrast to our earlier belief 

 we do not now think that cryptohaem a, as defined by us, is an artifact. Morrison 

 has suggested in his precirculated paper that cryptohaem a may arise from haem a, 

 in aged cytochrome oxidase preparations. We think that a thorough characterization 

 is necessary before this compound could be identified positively as cryptohaem a. 



Lemberg: The interesting observation of Morrison of the conversion of haem a into a 

 haem similar to cryptohaem a by a kind of autodestruction of active cytochrome 

 oxidase, requires further studies before it can be concluded that the haem in question 

 is cryptohaem a. The chemistry of our cryptoporphyrin a (see the precirculated 

 paper) and other observations of Parker {Biochim. biophys. Acta 35, 496, 1959), 

 make it appear unlikely that our cryptoporphyrin a is derived from haem a. Porphyrins 

 similar to but distinct from cryptoporphyrin a have been obtained by Miss Parker 

 from haemin a. Some of these porphyrins differed from cryptoporphyrin a in the 

 Rp of their methyl esters; one which had a similar ester- 7?/^ had a distinctly different 

 absorption spectrum. The cryptohaemin a of Morrison and Stotz may be the iron 

 complex of one of these porphyrins. Unless the identity of the porphyrin from their 

 cryptohaemin a with the cryptoporphyrin a now available as a well-crystallized methyl 

 ester has been established, the latter cannot be considered to be a compound derived 

 from one of the cytochromes a. 



Morrison: It would appear that we are all in agreement on that point, as we do not 

 consider cryptohaemin a to be an artifact either (see Morrison, Connelly and Stotz, 

 Biochim. biopliys. Acta 27, 214, 1958; Connelly, Morrison and Stotz, J. biol. Chem. 

 233, 743, 1958). Cryptohaemin a is, in our opinion, a naturally-occurring material 

 which may arise as the result of catalytic oxidation of the prosthetic group of the 

 cytochromes a. This may well be a situation comparable to the iron biliverdin complex 

 found in preparations of catalase. In identifying cryptohaemin a, we have used 

 the spectral properties published by Lemberg and Falk (Biochem. J. 49, 674, 1951) as 

 our criteria. Our compound fits these criteria very closely, particularly as our spectra 

 for the porphyrins were taken with pyridine as the solvent, and not with ether as 

 Lemberg assumed. 



The position of the alpha peak of the pyridine haemochrome is at 582 nyt both in 

 the original work of Lemberg and Falk and in the case of the compound we call 

 cryptohaemin a. In the more recently published work of the Sydney group, the alpha 

 peak is variously located at 579 m/i and 581 m//. It would appear that a clearer 

 definition of what is being called cryptohaemin a is in order. 



Lemberg : I certainly agree with the last point made by Morrison. It is not justified, e.g., to 



