70 OXIDATION-REDUCTION POTENTIALS 



pyocyanine). The system has been studied by Biihnann and Lund (1923), Richard- 

 son and Cannan (1929), and Biihnann and Berg (1930). At 30°C. and pH 7-0 the 

 electrode potentials of the system are expressed (in volts) by the formula : — 



E, = 0-06 + 0-03 f^^^^'^^, 

 [Dialuric acidj 



Hence two electrons are concerned in the reaction in accordance with theoretical 

 requirements. Richardson (1932) rejects the view that the system is of biological 

 significance. Hill and Michaelis (1933) find that iron is of importance in the estab- 

 lishment of the potential. 



CARBOHYDRATES 



An inert electrode immersed in a sugar solution slowly assumes a negative 

 potential difference with respect to the solution. This potential difference is regarded 

 as being due to an unknown reversible oxidation-reduction system present in the 

 solution. The potential is said to be independent of the nature of the sugar and 

 reaches a value of — 0-21 v. at pH 7-0 and at 40° C. (Goard and Rideal, 1924 ; Aubel 

 Genevois and Wurmser, 1927 ; Preisler, 1927 ; Wurmser and Geloso, 1928, 1929, 

 1931 ; Mayer, 1929.) 



SUCCINATE-FUMARATE 



The system succinate-fumarate appears to be reversible in the presence of the 

 appropriate enzyme (occurring in muscle and B. coli.). 



COOH.CH : CH.COOH + H^ ^ COOH.CH^.CHa.COOH. 



The system may be readily studied by the methylene blue technique in Thunberg 

 (1921) vacumn tubes. The possible importance of the system depends on the fact 

 that fumarate may act as hydrogen acceptor in bacterial systems and this accounts 

 for some bacterial respiration processes. The constant for the system is stated to 

 be, Eo -= + 0-005 V. (Thunberg, 1925). Lehmann (1930) could obtain a readily 

 reproducible electrode potential in the succinate-fumarate-succinic dehydrogenase 

 system only in the presence of oxidation-reduction indicators, the potential observed 

 being the same as that obtained by Thunberg. Wurmser and de Boe (1932) investi- 

 gated the lactic acid-pyruvic acid system (in the presence of a bacterial autolysate) 

 and observed a normal potential of — 0-2 v. (See also Barron and Hastings, 1934 ; 

 Baumberger, Jiirgensen and Bardwell, 1932). 



Laid (1937) finds the oxidation-reduction potential of the malic-oxaloacctic acid 

 system to be — 0-1G9 v. at pH 7 which approximates to that of the lactic-pyruvic 

 acid system and much lower than the succinate-fumarate level. Nevertheless, 

 in muscle oxaloacetic acid is reduced more rapidly than fumaric acid. 



The /^-hydroxy butyric : acetoacetic acid system has been found to be a 

 reversible oxidation-reduction system in the presence of tissue preparations and the 

 normal potential at pH 7 is given as 0-282 v. by Green, Dewan and Leloir (1937) 

 and - 0-293 v. by Hoff-Jorgensen (1938). 



