VITAMINS, ANTIBIOTICS, AND GROWTH 



345 



Only four sugar derivatives have been found to be capable of in- 

 creasing the synthesis of L-ascorbic acid when supplied to germinating 

 seedlings or of increasing the excretion of L-ascorbic acid after injec- 

 tion into rats. These are the gamma lactones of L-gulonic and L- 

 galacturonic acids, the gamma lactone of D-glucuronic acid, and the 

 methyl ester of D-galacturonic acid (Mapson, 1958). None of these 

 four compounds (Figure 9) is effective against scurvy in guinea pigs. 

 The conclusion is that the inability of the guinea pig and presumably 

 of man to synthesize ascorbic acid is due to the absence of the specific 

 enzymes for carrying out the final stage of the reactions shown in 

 Figure 9. 



The enzymes in rat liver that convert the lactones of gulonic and 

 galacturonic acids into ascorbic acid are present in the mitochondrial- 

 microsomal fractions. These particles will not oxidize the free acids. 

 The corresponding fraction from guinea-pig liver will not produce 

 ascorbic acid from the two lactones mentioned above. 



Further discussions and additional references to the biosynthesis 

 of the vitamins are in the review by Brown ( 1960 ) . 



Vitamins and the growth of human cells 



Mammahan cell cultures have been investigated for their require- 

 ment for growth factors by Eagle (1959) and others. Eagle's medium 

 contains 29 components, including 13 amino acids, 8 vitamins, 6 in- 

 organic ions, glucose, and 5 to 10 per cent of whole or dialyzed serum 

 protein, which may of course supply any number of "unidentified 

 factors" that are bound to the protein. However, the studies have 

 shown a clear need for the following vitamins in the growth of normal 



H OH 



V- 



Hi 



OH 



HOCH 

 HCOH 

 HC- 



0- 



H OH 

 \/ 



C — 



H(j:OH 



I HCOH 

 I 



0- 



90-n 

 '9^ 



th- 



.OH 



|H9 



I— r 



HOCH 



HOCH 

 I 

 HC 



CO 



Hoin 

 CH2OH 



CO — I 



Hoi I 

 li 



HOC I 



HOCH 

 CHsOH 



(a.) 



D-qlucose D-qlucurono L-qulono L- Ascorbic 



-lactone -lactone acid 



/ 



— ^ Methvl > L-qaloctono 



D-qolocturonate - lactone 



Figure 9. Formation of ascorbic acid from glucose or galactose. 



(b.) D-qolactose 



