62 



OXIDATION-REDUCTION POTENTIALS 



rljv;^^/d ^-CH2-NH— < >-CO-NH-C-CH?CH2<:OOH 



4h ^ COOH 



Pterin 



p-Aminpbenzoic 

 ^ acid 



Glutamic 

 acid 



-^ 



PteroyI 

 Pt ero ylg iutamic Acid (Folic Ac! d) 



The combination of pterin, p-amino benzoic acid and glutamic acid suggests some 

 of the functions of the vitamin. The similarity of the pterin portion of the molecule 

 to riboflavin is evident. p-Amino benzoic acid appears to be a growth factor for some 

 micro-organisms and the chemotherapeutic effect of sulphanilamides may be due to 

 antagonism to this jjortion of the molecule. The great importance of glutamic acid 

 in the nutrition of micro-organisms is being increasingly realised. It is interesting to 

 note that xanthopterin occurring as a yellow pigment in the wings of butterfl.ies is 

 apparently without metabolic significance and the distribution of the pigment when 

 ingested by guinea-pigs is of interest. The inhibition of mammary tumours by 

 pteroyl-triglutamic acid may prove of importance. 



TOCOPHEROL, VITAMIN E 



Vitamin E or tocopherol, the antisterility factor for female rodents, is also an 

 anti-oxidant and the question arises w^hether the physiological activity is associated 

 with oxidation-reduction changes. Unlike anti-oxidants such as hydroquinone, 

 tocopherol (I) contains only one unsubstituted phenol group and the first oxidant 

 isolated (II) has the ring structure ruptured so that the oxidation is not reversible. 

 The possibility still remains, however, that reversible oxidation-reduction with an 

 intermediate radical might occur, the semiquinone differing from tocopherol by one 

 •electron. 



HO 

 C 



CH3 ^^ CH3 



Hsk. Ao/<^M~^^3lO% Jh ^'^ "33 



CH. ^^ ^'6^33 CH3 ^ ^" 



Toco phero l 



Evidence for such a radical has been lacking, but Michaelis and Wollman (1949) 

 ■dissolved tocopherol in organic solvents, froze the solution in liquid air, forming a 

 glassy film and this was irradiated with ultra-violet light. The radiation supplied 

 energy locally to remove an electron and an orange-coloured free radical accumulated. 

 The low temperature prevented thermodynamic equilibrium being established homo- 

 genously through the film and local accumulation of the radical was possible. 

 Immediately the temperature was raised, homogenous equilibrium occurred and the 



