432 IX. HEMATIN ENZYMES, II 



Soret band, shifted toward the red; choleglobin does not possess a 

 similar band. Verdohemochrome {cf. Chapter X) is reduced by 

 dithionite to a yellow compound with a similar band (e^M = 50), but 

 its absorption in the visible part of the spectrum is quite different. 

 Fluoride and carbon monoxide do not cause any spectroscopic changes. 

 The reduced enzyme is not autoxidizable in neutral or alkaline solu- 

 tions, but is autoxidizable below pH 5. The enzyme is inhibited by 

 10-" M cyanide (86%), 10-^ M hydroxylamine (30%), and IQ-^M 

 azide (66%); it is not inhibited by carbon monoxide. The PZ is 75, 

 if calculated from the initial reaction velocity, but the latter drops 

 rapidly. Polyphenols, p-phenylenediamine, and ascorbic acid can 

 serve as substrates. Hydroquinone reacts rapidly with the green 

 hydrogen peroxide compound, restoring the ferriperoxidase. 



Agner believes that myeloperoxidase may be the compound with absorp- 

 tion band at 639 m/x observed by Warburg in Acetobacter pasteurianum 

 (Chapter VIII. Section 3.6.3.), when the latter is aerated in the presence of 

 cyanide. There is, however, no indication of a band in the red in the reduced 

 state in the organism, which should be the case if the band were due to a 

 substance similar to myeloperoxidase. 



3.7. Cytochrome c Peroxidase 



An interesting enzyme has been discovered in bakers' yeast by 

 Hogness and his collaborators {1,41, 4-2) ■ It was first believed to be 

 water-soluble cytochrome c oxidase, but later it was found that its 

 activity depended on the presence of hydrogen peroxide in the reduced 

 cytochrome c preparation; hence catalase prevented its action. The 

 peroxide probably owed its presence to the use of dithionite as reducer 

 in the preparation of cytochrome c. 



The enzyme is isolated from yeast by toluene autolysis, followed 

 by ammonium sulfate - trichloroacetic acid precipitation, solution of 

 the precipitate in water, fractional alcohol precipitation, and adsorp- 

 tion to 7-aluminum hydroxide. On reduction with dithionite in the 

 presence of pyridine it yields pyridine protohemochrome ; a spectro- 

 photometric estimation of this showed that the enzyme contained 

 about 0.3% protohematin. 



The ferric enzyme has weak absorption bands at 6*^0 m/i (cmM = ^-0) and 

 500 mM (cmM = 10.5) and a strong Soret band (fmM = 9'^). Dithionite 

 reduces it to the ferrous compound which has an absorption band at 560 mpt, 

 a Soret band at 437.5 m//. and possibly atso a weak band at 670 m^t. 



The ab.sorption spectrum of the hydrogen peroxide complex resembles 

 that of the horse-radish peroxidase-hydrogen peroxide compound II of 



