Ascorbic Acid As a Growth Hormone 



729 



such, accumulated in the treated tissues largely in the oxidized form, 

 dehydroascorbic acid (DHA) (Table 2). It was also observed that the 

 inhibition of respiration and growth is much better correlated with 

 the internal concentration of DHA than with that of AA (12) (Figure 

 2). Moreover, pretreatment of the pea internode segments with 0.5 

 per cent diethyl dithiocarbamate (an inhibitor of AA oxidase), which 

 markedly inhibited the accumulation of DHA within the treated tis- 

 sues, consistently reduced and in some experiments completely sup- 

 pressed the inhibiting effect of AA treatment on growth (17) (Table 3). 

 These results were interpreted as evidence that DHA, rather than 

 AA, is the real inhibitor in the case of the treatment with AA. In sup- 

 port of this view, a series of experiments on the effects of AA, DHA, 

 and 2,3-diketogulonic acid on metabolic systems in vitro, show that 

 DHA at concentrations between 10"^ and IQ-^M markedly inhibits 

 several dehydrogenase systems (14), as well as the oxidative and phos- 

 phorylative activity of mitochondrial preparations (2, 10) (Figure 2). 

 This seemed to provide a satisfactory explanation for the inhibitory 

 effect of AA on respiration in vivo, and also to suggest that at least 

 part of the growth effect could depend on the inhibition of some step 

 of respiratory metabolism. 



Table 2. The effects of diethyldithiocarbamate (DIECA) pretreatment on growth 

 mhibition by ascorbic acid (A A) (11). 



Average 

 0.0 

 2.0 



9.6 

 5,8 



9.1 

 7.8 



40 



14 



