162 THE BIOLOGY OF HYDRA : 1961 



TABLE 7 

 Action of the purified inhibitor on cytochrome oxidase 



Material Inhibitor to Cytochrome Inhibition 



tissue ratio oxidase activity 



fig.: nig. Qoo (wet weight) % 



Mouse Hver homogenate ■ 96 



Mouse liver homogenate 



plus purified inhibitor 



(1.16 /ig. protein N) 1.16 : I 110 0.0 



Each vessel contained 1.0 mg. of aqueous liver homogenate in final volume of 

 2.9 ml. 



flavin moiety and components of the intermediary portions of 

 succinoxidase, terminating at cytochrome c. The exact nature of 

 this system in the enzyme preparation we used is not thoroughly 

 understood. If the purified inhibitor is preincubated with the mouse 

 hver homogenate, we find significant inhibition of succinate-cyto- 

 chrome-c reductase. The inhibition, although less than with succin- 

 oxidase, is pronounced and occurs with the concentration of inhib- 

 itor which produces 50% reduction of succinoxidase (Table 8). 



Our overall results in this area of the investigation lead us to 

 postulate that the inhibition is specific [based on criteria of Keilin 

 and Hartee ( 4 ) and Slater ( 22 ) ] and that the reduction of cyto- 

 chrome c is blocked, that is, the inhibition occurs on the substrate 

 side of cytochrome c. Fmthermore, since there is no evidence for 



TABLE 8 

 Effect of the purified inhibitor on succinate-cytochrome-c reductase 



Material Inhibitor to Reductase activity Inhibition 



tissue ratio ( cyt. c reduction at 550 m/x ) 

 fig.: mg. fi moles in 10 min. % 



Mouse liver homogenate 0.0237 ■ 



Mouse liver homogenate 



plus purified inhibitor 



(0.0116 /ig. protein N) 0.058 : 1 0.0209 12 



Mouse liver homogenate 



plus purified inliibitor 



( 0.0309 /ig. protein N) 0.174 : 1 0.0094 60 



Aqueous liver homogenate preincubated with purified inhibitor for 30 minutes 

 at room temperature. Each cuvette in assay had 0.2 mg. of homogenate. Volume in 

 each cuvette = 3.0 ml. 



