LUIS F. LELOIR 



of asymmetry may be suspected, such as a substitution, a break- 

 age of the carbon atom chain, or the formation of a double bond. 

 Further work using labeled compounds would be of the utmost 

 interest. 



Another inversion at position 4 has been detected recently. 

 This is the transformation of UDP-acetylglucosamine (UDPAG) 

 (IV) into UDP-acetylgalactosamine (UDPAGA) (V) by liver 

 enzymes. The use of yeast as starting material led to the isola- 



C 



/ 



(UDP) 



HCNH-CO-CHg 



HOCH 

 I 

 HCOH 



I 

 HC 



G- 



/ 



(UDP) 



O 



HCNH-CO-CHs 

 I 

 HOCH 



I 

 HOCH 

 I 

 HC 



O 



CH2OH 



(IV) 

 UDP-acetylglucosamine 



CH. 



OH 



(V) 

 UDP-acetylgalactosamine 



tion of pure UDPG and pure UDPAG (4), but a study of these 

 compounds in liver showed that instead of UDPG, the product 

 obtained was a mixture of UDPG and UDP-galactose. The 

 same occurred with the acetylamino derivatives. Instead of 

 UDP-acetylglucosamine as in yeast, the product obtained from 

 liver contained about 20% of the acetylgalactosamine deriva- 

 tive (20). Further investigation showed that liver extracts 

 catalyze the transformation of UDPAG into UDPAGA, and this 

 may be the starting point of the study of a practically unexplored 

 field : the enzymology of galactosamine-containing compounds. 

 Studies on uridine nucleotides have been extended in several 

 directions. The list of sugars which have been found combined 

 with UDP is — glucose, galactose, acetylglucosamine, acetyl- 

 galactosamine, glucuronic acid, and three hexosamine amino 

 acid compounds (19). It has also been found that UDPG can 

 act as a glucose donor to fructose, to fructose-6-phosphate, or to 

 glucose-6-phosphate, yielding sucrose, sucrose phosphate, or 



592 



