518 



LIGHT AND LIFE 



were sufficiently decelerated to be conveniently measurable with a 

 recording spectrophotometer at room temperature. 



Effect of Vitamin K 



In fresh preparations of chromatophores the reduction of oxidized 

 cytochrome in the dark was not influenced by the addition of added 

 cofactors (compare Table 2) . However, as shown in Fig. 8, in aged 

 preparations the reduction of the oxidized cytochromes was greatly 

 accelerated by the addition of vitamin K, either in the oxidized form 

 (vitamin K3) or in the reduced form (vitamin K5) . The effect of 

 vitamin K, as an electron carrier, in accelerating the reduction of oxi- 

 dized cytochrome depended on the presence of chromatophores. With- 

 out chromatophores, using a purified cytochrome C2, a hundredfold 

 greater concentration of reduced vitamin K was required to reduce 

 the oxidized cytochrome. 



The observed effects of vitamin K in catalyzing the reduction of 



FRESH PREPARATION 

 (ILL.-D) 



AGED PREPARATION 

 (ILL.-D) 



0.0 



a. 

 E 



O 



CM 



O 



d 



-0.1 - 



-0.2 - 



Light off 



t 

 Light off 



Fig. 8. FJrcct of vilaniin K and txlicr tofaclois on tiic reduclion cytochrome 

 c, in cell-free preparations of CJnoiiuitiuin. Ilic cylot lirome was oxidi/ed by pre- 

 vious illumination (cf. Fig. 7). The reaction mixture included in a hnal volume 

 of 3.0 ml. dialyzed cell-free suspension (PS) containing 0.06 trig bacteriochlorophyll, 

 0.02 (Ltmoles of purified cytochrome Cj and 0.03 ^umolcs of the respective cofactors. 

 Differeiue in optical dcnsitv was measured on a IJccknian Df specliophotometer 

 with an atlaciied plioionudtiplier, and using as contiols cuvettes, kept in the dark, 

 with the respective cofactor omitted (Nozaki, Ogata, and Anion, 114). 



