VITAMINS Gl 



The normal potential (Eq) was found to be + 0-3895 v., and the slope of the 

 EflYpH curve was found to change from 0-06 to 0-03 at pH 4 and to remain at " 0-03^ 

 slope " as far as pH 8-6. It was concluded that dehydroscorbic acid does not exist 

 in tissues. 



Ascorbic acid has been determined potentiometrically by Becker and Digleria 

 (1937), Gillam (1945), and by Kirk and Tressler (1939). 



Ascorbic acid is widely distributed through the plant kingdom increasing during 

 germination and apart from being useful to animals who eat the plant products it 

 probably has biological significance to the plant. Like other compounds themselves 

 subject to oxidation-reduction reactions such as catechol, ascorbic acid acts as an 

 anti-oxidant and protects susceptible compounds from oxidation. Some recent work 

 by Virtanen and Hansen (1949), throws light on the possible importance of ascorbic 

 acid to plants. The cotyledons of pea seedlings are rich in vitamin C and removal of 

 the cotyledons stunts growth. Addition of ascorbic acid to the cotyledon-less 

 seedlings improves growth and it has been found to lower the oxidation-reduction 

 potential of the plant. Other reducing substances such as reductone, cysteine and 

 glutathione had the same beneficial effect. Administration of vitamin C to plants 

 already having a normal supply can restrict growth due to the development of too 

 low an oxidation-reduction potential. It is concluded that the function of ascorbic 

 acid in the plant is to regulate the oxidation-reduction potential at an optimum level. 



Improper cooking of vegetables results in destruction of vitamin C, traces of 

 copper markedly accelerating the oxidation to dehydro-ascorbic acid : — 



CO — COH CO — CO 



6 jcoH i /CO 



iHOH CHOH 



iHzOH CH2OH 



Ascorbic Dehydro-ascorbic 



acid acid 



A number of enzyme systems oxidise ascorbic acid ; these include catecJiol 

 oxidase, cytochrome, peroxidase and a specific ascorbic acid oxidase, which is a 

 copper protein complex (see page 54) inhibited by copper precipitants. 



FOLIC ACID ; PTEROYLGLUTAMIC ACID 



Administration of folic acid improves blood regeneration in pernicious anaemia 

 (the cobalt complex already mentioned being necessary for prevention of spinal cord 

 degeneration). It has been found that the factor necessary for the growth of 

 Lactobacillus casei, for the growth of chicks and Vitamin M from liver and yeast used 

 to alleviate pregnancy anaemia in India are all identical with folic acid, which i& 

 pteroyl-glutamic acid with the following structure: — 



