76 



OXIDATION-REDUCTION POTENTIALS 



which penetrate into the cell interior of starfish eggs (CO2 and NHg) affect tlie pH 

 and hence the E^^ of the cell whilst HCl and NaOH which are non-penetrating do not. 

 Machlis and Green (1933) using starfish sperm concluded that many of the more 

 highly reducing dyes were reduced by enzyme action and that the anaerobic poten- 

 tials investigated may be amenable to thermodynamic treatment but that aerobic 

 potentials as measured in dye experiments did not correspond to an intrinsic property 

 of the cell. 



It is evident that the results obtained by different workers by introducing 

 artificial dyes into cells are somewhat confused and contradictory. Evidence as 

 to the oxidation-reduction conditions of the cell interior may be obtained by observa- 

 tion of the behaviour of naturally occurring pigments which are normal constituents 

 of the cell. Some of the disadvantages inherent in the use of dyes are not encoun- 

 tered when considering natural pigments in their native cells, but other difficulties, 

 due to the abnormal behaviour of pigments in the presence of other cellular con- 

 stituents may arise. 



Hermidine occurs in green shoots, etc., of Mercurial is perennis and is at least 

 ■95 per cent, reduced, so that at pH 7-6 the E^ of the cells must be — 0-09 volt, or 

 more negative than this (Cannan, 1926). 



Echinochrome, on the other hand, which occurs in many echinoderms is mainly 

 in the oxidised condition. So that, assuming the pH to be 7-7, the Ei, of cells con- 

 taining echinochrome must be less negative than —0-2 v. if the pigment is at least 

 99 per cent, oxidised (Cannan, 1927). 



In the nudibranch Chromodoris zebra, the pigment is mainly in the oxidised form 

 so that the potential must be less negative than — 0-1 v. (Preisler, 1930). 



TABLE 17 

 Approximate Electrode Potentials of Biological Systems 



(In the case of pigments, etc., the potential of the half reduced 

 system, E^,' at pH 7-0 is given. All the results are quoted in volts.) 



TISSUE AND CELL SUSPENSIONS 



Ehrlich (1885) injected dyes into an animal and examined the condition of the 

 •dye in various organs of the animal immediately after death and so obtained some 

 idea of the oxidation-reduction conditions of different tissues, but the significance 



