IV. BIOCHEMICAL SYSTEMS 219 



b. Manganese 



Manganese has l)een reported as lieing a necessary cof actor in the syn- 

 thesis of ascorbic acid. Seedlings of Avena, Triticum, Hordeum, Phaseolus, 

 Miingo, and Cicer anetinum were found to contain more ascorbic acid when 

 grown in the presence of manganese salts than when grown in their ab- 

 sence.^* The ascorbic acid content of tomatoes grown in soils low in man- 

 ganese was found to be lower than that of similar plants grown in soils 

 with higher manganese contents.''® This work was extended to animal tis- 

 sues, and it was reported that with both rat and guinea pig liver tissues 

 the formation of ascorbic acid was increased in vitro if the tissue was sup- 

 plied with mannose, glucose or galactose, and manganese salts; the increase 

 did not occur if sugar alone was supplied. ^^ With guinea pig liver a higher 

 concentration of manganese was found to be essential. Similar findings were 

 reported from experiments when rats or guinea pigs were injected with the 

 sugar and manganese salt. 



These results with animal tissue have not, however, been confirmed by 

 later workers.*^ WTien scorbutic guinea pigs were injected with both man- 

 nose and manganese salts there was no evidence, either by the phosphatase 

 test or by an analysis of tooth structure, of any protection against scurvy, 

 which developed as cjuickly in injected animals as in control animals. The 

 hypothesis that manganese is an essential cofactor in the synthesis of as- 

 corbic acid needs further investigation. 



c. Molybdenum 



The possible role of molybdenum has recently been emphasized. ^^ It has 

 been shown that the tissues of plants deficient in this element are low in 

 ascorbic acid. Neither disparity in growth nor lack of chlorophyll could 

 account for this. It is too early to decide whether molybdenum affects the 

 sjTithesis of ascorbic acid directly or whether the lack of it leads to a dis- 

 turbance in the normal ascorbic acid-dehydroascorbic acid equilibrium in 

 the cell. The role of molybdenum in higher plants is thought to be closely 

 connected with the assimilation of nitrate nitrogen;*" molybdenum require- 

 ments appear to be much reduced when nitrogen is supplied as ammonium 

 salts. *• It may therefore function in the processes concerned with the reduc- 

 tion of nitrate. The suggestion that ascorbic acid may also be associated 



'' M. X. Rudra, Nature 141, 203 (1938); Biochem. Z., 301, 238 (1939). 



« J. B. Hester, Science 93, 401 (1941). 



^' M. X. Rudra, Nature 144, 868 (1939). 



« J. T. Skinner and J. S. McHargue, Am. J. Physiol. 145, 566 (1946). 



" E. J. Hewitt, S. C. Agarvvala, and E. W. Jons, Nature 166, 1119 (1950). 



" E. J. Hewitt and E. W. Jons, J. Pomol. Hort. Set. 23, 254 (1947). 



" E. G. Mulder, Plant and Soil 1, 94 (1948). 



