328 D. B. MoRELL, J. Barrett, P. Clezy and R, Lemberg 



the pyridine and 25 for the native globin compound to 15-5 for the 

 apoperoxidase compound. 



The ratio of extinctions y-band/a-band varies from 3-3 for the imidazole 

 compound to 5-9 for the apoperoxidase compound, averaging 4-7 for the 

 haemoproteins. The ratio y-band/a-band for the difference spectra 

 (AFe++ — Fe+++) is similar to this (e.g. 4-4 for the ox serum albumin com- 

 pound); this is in good agreement with the ratio 4-5 observed by Chance and 

 Yonetani (1959) for cytochrome a. It has often been stated that this ratio is 

 abnormally low for haemoproteins. A higher ratio is, however, by no means 

 general for haemoproteins. For cytochrome c, e.g. it is 4-8. Cytochrome a^ 

 rather than cytochrome a appears to have an abnormal y/a ratio. 



The Soret band of haem a lies at 410^15 m/;, but is shifted towards longer 

 wavelengths by combination with nitrogenous compounds, e.g. to 446 m/^ 

 by cyanide, 442 m// by globin, 441 m^ by methylimidazole and peroxidase 

 apoprotein, 435 m/^ by the serum albumins, and 430 m/f by pyridine or 

 alkah-denatured proteins. The position of the y-band of cytochrome a^ 

 (445 ran) thus resembles those of haem «-methyhmidazole, haem a-globin and 

 haem ^-peroxidase. All the nitrogenous compounds, and also carbon mon- 

 oxide alone, increase the Soret band of haem a. 



Carbon Monoxide Compounds 



Carbon monoxide shifts the a-absorption band always towards the red by 

 5-1 1 m/^ (with the exception of haem a at pH 9, but not at pH 7-5). This also 

 holds for the compounds with denatured proteins, whose CO compounds 

 have absorption maxima at 583-584 m^t. The a-bands of the CO-haemo- 

 proteins and CO-haemochromes lie at 597-605 m/^. Thus so far no CO-haem 

 a compound with an absorption maximum at 590 m/i has been observed, 

 and no compound has as yet been found whose a-absorption band is shifted 

 by 15 m/t towards the blue by combination with CO, as is assumed for 

 cytochrome ^3. In this respect also, cytochrome a^ appears to be an unusual 

 haem a compound. 



The position of the Soret band of the CO-compounds including CO-haem a 

 has usually been found between 428 and 435 m/f, in agreement with the posi- 

 tion of this band of cytochrome a^. For the denatured protein CO compounds 

 the Soret band was found at 424 m/^. 



In summarizing; we have obtained no haemoprotein a which resembles 

 cytochromes a and a^ in all properties. In contrast to cytochrome a our 

 haemoproteins combine with carbon monoxide, and their a-bands lie at 

 590-596 m/( instead of 605 m/<, but their y/a ratio and the position of the 

 Soret band are those of cytochrome a. No haem a compound has been found 

 which like cytochrome a^ forms a carbon monoxide compound with shift of 

 the absorption maximum towards the blue, or a haemoprotein with a y/a 

 ratio of 15 reported for cytochrome a^ by Chance and Yonetani (1959). 



