184 E. R. REDFEARN 



succinic cytochrome c reductase activities had fallen to approximately 50% 

 of the original activities. Polar solvents, such as ether and acetone, differ 

 from non-polar solvents in that cytochrome oxidase is much more readily 

 inactivated. Thus after one or two extractions with ether, cytochrome 

 oxidase becomes the rate-limiting step in the respiratory chain. 



Although much remains to be done on the correlation between enzymic 

 activites and lipid content of respiratory chain particles, certain conclusions 

 can be drawn from these preliminary experiments. Treatment of heart- 

 muscle preparations with organic solvents appears to have three principal 

 effects : (i) the physical action of the solvent producing changes in particle 

 size and morphology, (ii) the removal of lipid from the particle by solution 

 in the solvent, and (iii) the retention by the particles of small amounts of 

 the solvent by surface adsorption or solution in the lipid. The first of these 

 is undoubtedly the cause of the increased enzyme activities obtained after 

 shaking the preparation with the solvent. This treatment probably results 

 in the breaking down of large particles or aggregates into smaller particles 

 or in changes in particle structure which allow an easier access of the 

 reactants to the particles. The effecc is probably analogous to the action 

 of surface-active agents and the effect of freezing and thawing, processes 

 which also result in increased enzyme activities. The solvent probably also 

 displaces endogenous cytochrome c, which explains why solvent treated 

 particles show a complete requirement for added cytochrome c. 



With regard to the second effect, lipid is removed only with great 

 difficulty by non-polar solvents but more readily by polar solvents, e.g. 

 certain lipid components, such as ubiquinone, can be almost completely 

 removed by extraction with ether. Cytochrome oxidase activity appears to 

 be much more sensitive to polar solvents than to non-polar solvents. 



The third effect, inhibition by the solvent itself, can be reversed by any 

 one of a number of methods which depend on the removal or displacement 

 of the solvent. It is interesting to note that this type of inhibition depends 

 upon the structure of the particular solvent. Weber and Wiss [10] have 

 show^n with the //-alkanes, those with 6-7 carbon atoms are the most 

 active. Even more potent inhibitors are the vitamin K., analogues with 

 short side-chains. Weber and Wiss [10] showed that like the organic 

 solvents, the inhibition due to these substances could be reversed by 

 vitamin K,, phvtol and ubiquinone. Redfearn, Pumphrey and Fynn [11] 

 suggested that the action of naphthoquinone inhibitors described by Ball, 

 Anfinsen, and Cooper [12] could be explained in terms of a similar non- 

 specific physical effect. Thus it could be imagined that the short lipophilic 

 side-chains dissolve in the lipid phase of the particle with the projecting 

 layer of large naphthoquinone nuclei acting as a barrier to the reactants. 

 Recently, Herdlin and Cook [13] have presented evidence which appears 

 to support this idea. 



