HOKMONES 



71 



Tissues also catalyse the a-hydroxyglutaric : a-ketoglutaric acid reaction 

 giving a reversible system with a normal potential of — 0-07 v. at pH 7. 



The alanine : ammonium pyruvate system in the presence of kidney d-amino 

 oxidase and Nile blue (as a carrier) has Eo^ — 0-066 v. at pH 7-3 (Wurmser and Filitti- 

 Wurmser, 1938). 



ADRENALINE 



Ball and Clark (1931) have investigated the adrenaline system ; they plotted 

 potential-time curves of mixtures of oxidant and reductant and by extrapolation 

 obtained a value for the potential at zero time. The potentials characteristic of the 

 system are closely similar to those of the closely related pyrocatechol system, but the 

 stability is lessened by the presence of the side chain. It is suggested that the 

 reduction potential of tissues is such as to protect the adrenaline from oxidation and 

 rapid destruction. 



Ball and Chen (1933) emphasise the instability of the oxidant of adrenaline and 

 related compounds and give as the potential of the half-oxidised system (Eo') at 

 pH 7-0 a value of -f0-38v. 



These workers measured the instability of a number of substances by observing 

 the alteration of the electrode potential with time. Table 14 shows the alteration 

 in potential (given in millivolts per second) of catechol and adrenaline in solutions 

 of different pH. The more unstal3le the system, of course, the greater is the change, 



dE,. 

 dt 



TABLE 14 

 e' Values and Instability Factors of Catechol and Adrenaline at different pH (30°C.> 



It will be noted that there is a general increase in instability as the systems- 

 become more alkaline. In table 15 are given the instability factors (alterations of 

 potentials with time) of a number of related compounds studied by Ball and Chen. 



