308 



T. HoRio, I. Sekuzu, T. Higashi and K. Okunuki 



P-cytochrome oxidase are similar to those of ox-heart cytochrome oxidase 

 (Okunuki, 1941), except that P-cytochrome oxidase rapidly oxidizes these 

 reagents regardless of the presence or absence of P-cytochrome-551 and 

 P-blue protein, whereas the animal cytochrome oxidase is inactive unless 



0.20r 



0.16 



0.12 



0.08 



0.04 



—I 1 1 — 



CYTOCHROME C 

 CYTOCHROME C, 



-I 1 I 



CYTOCHROME C ADDED 



at 553 mjLi 



8 



TIME IN MINUTES 



Fig. 4. Oxidations of reduced cytochrome c, and cytochrome Cj by cytochrome a. 

 The cuvette contained 3-3 x 10""^ m phosphate buffer of pH 7-4, 0-5% cholic 

 acid, 1-4 X 10~* m cytochrome o, and cytochromes c and Cj, total volume made 

 to 3-0 ml with water. Reactions were carried out at 15°C. The oxidations were 

 initiated by the addition of cytochrome a, and the oxidations of cytochrome c, 

 and cytochrome c^ were measured by the decrease in optical densities at 550 m^w, 

 and at 553 m// (each a-absoq3tion maximum), respectively. Curve A, oxidation 

 of 0-9 X 10^ M cytochrome c\ curve B, oxidation of 1-4 x IO~^m cytochrome 

 c^. The arrow shows the time when 2 x 10~® m cytochrome c was added. 



cytochrome c is present. The oxidation of the chemical reductants, P-cyto- 

 chrome-551 and P-blue protein, by P-cytochrome oxidase is strongly inhibited 

 by carbon monoxide and cyanide. The inhibition by carbon monoxide is 

 reversed by light. The absorption peak at 625 m/f and the shoulder around 

 450 m/^ of the reduced P-cytochrome oxidase are altered by carbon monoxide, 

 but the other absorption peaks exhibit no such alteration. The absorption 

 peaks of the oxidized P-cytochrome oxidase are not so significantly influenced 

 by cyanide in spite of its strict inhibition. The hydroquinone oxidation by the 

 oxidase reaches its half-maximal and full-maximal rates under the gas phase 



