330 



Discussion 



Warburg, O. & Gewitz, H. S. (1951). Hoppe-Seyl. Z. 288, 1. 



Warburg, O., Gewitz, H. S. & Volker, W. (1955). Z. Naturforsch. 10b, 541. 



DISCUSSION 



Model Systems for Cytochrome Oxidase 



Absorption Spectra of Ferro- and Ferri- Compounds of Haem a 



By R. Lemberg (Sydney) 



Lemberg : With regard to the compounds of haem a and haematin a there appears to be, 

 as in protohaematin compounds, a distinction between ferric compounds with absorp- 

 tion bands at 635 m/i and 500 m/* (probably 'ionic') and ferric compounds with a 

 single band at about 590 m/i similar to but lower than that of the ferrous complex 

 (probably 'co-valent'). As in protohaematin compounds, the (ferric) haematin 

 a-proteins appear spectroscopically to be mixtures of the two types, with the 'co- 

 valent' type prevailing in haematin a-globin and the serum albumin compounds, and 

 'ionic' compound prevailing in haematin a-apoperoxidase. 



This seems quite distinct as there appears to be only one single characteristic band 

 for each compound at 635 and 590 m/< respectively. There is, however, a rather poor 

 correlation between A m^ Fe++-Fe+++ for the Soret bands and the ratio £635/e590 m/i 

 in the ferric compounds as shown in Table 1 . 



Table 1 



The reason that CO always shifted the absorption band of all our models in the 

 visible to longer wavelengths, not to shorter ones as with cytochrome Oj, does not 

 appear to be due to a^ being a more 'ionic' type of compound than any of our model 

 haemoproteins a. Even the compound with apoperoxidase in which the absorption 

 spectrum of the ferric compound as well as A m/t Fe++-Fe+++ indicate a high degree 

 of 'ionic' nature, still gives a shift to the red with CO. Moreover, CO always shifts 

 the Soret band to shorter wavelengths, with our model haemoproteins as well as with 

 cytochrome a^. 



The haemochromes a formed with alkali-denatured proteins, with bands 13-14 m,« 

 to the blue compared with pyridine haemochrome a are unusual. High pH is necessary 

 for their formation. Urea-denatured globin at pH 9 gives a band quite close to that 



