Ill ATP AND RELATED NUCLEOTIDES 39 



Hyaluronic acid is a linear polymer of alternating N-acetyl-D-glucosamine and D-glucuronic 

 acid residues joined in p-glycosidic linkage. The molecular weight may vary between 

 300,000 and 1 ,500,000, depending on the source. Cell free extracts of the Rous sarcoma 

 synthesize oligosaccharides of the hyaluronic acid chain when incubated with labelled 

 substrates (Glaser and Brown, 1955) as shown in reactions b) and c) : 



b) UDP-N-acetyl('''C) -glucosamine -^ UDP-glucuronate — » '■'C-oligosaccharide 



c) UTP + N-acetyl(''»C)-glucosamine-6-phosphate + UDP-glucuronate -^ '•»C-oligo- 



saccharide 



UDPG and DPN"^ can replace UDP glucuronate in reactions b) and c) due to the presence 

 of the dehydrogenases required for UDP glucuronate synthesis (Strominger et ai, 1954) : 



Liver, tumor 



d) UDPG + 2DPN^ > UDP-glucuronate + 2DPNH2 



The carbon skeletons of glucuronate and N-acetyl glucosamine are both derived from 

 glucose without prior fission of the carbon chain. The synthetis of glucuronate will be 

 discussed in connection with ascorbic acid biosynthesis. N-acetylglucosamine may be 

 derived from glucose as follows : 



e) Hexose-6-phosphate + glutamine — > glucosamine-6-phosphate — glutamic 



f) Fructose-6-phosphate + NH3 " — ^ glucosamine-6-phosphate 



g) Glucosamine-6-phosphate + acetyl-CoA ^N-acetyl-glucosamine-6-phosphate + CoA 



mutase 

 h) N-acetylglucosamine-6-phosphate ' ^ N-acetylglucosamine- 1 -phosphate 



i) Glucosamine + ATP —> glucosamine-6-phosphate + ADP 



PP-uridyltransferase 



j) N-acetylglucosamine- 1 -phosphate + UTP ' t UDP-N-acetyl- 



glucosamine 



Reactions e) and g) have been observed in Neurospora (Leloir and Cardini, 1953, 1956) 

 while reaction f ) takes place in kidney, liver, and other animal tissues. Reaction h) occurs 

 in the Rous sarcoma, Neurospora, and animal tissues. Reaction i) is catalyzed by hexokinase 

 of yeast or brain (Leloir, 1951 : Harpur and Quastel, 1949). Enzymes which phosphorylate 

 galactosamine to galactosamine-i -phosphate also occur in liver and yeast (Leloir and 

 Cardini, 1953). 



In connection with UDP galactose, mention should be made of another uridyl transferase 

 enzyme of yeast and liver (Maxwell, 1956): 



GP-uridyl transferase 



k) galactose- 1 -phosphate + UDPG " r UDP-galactose + glucose- 1- 



phosphate 



Reaction k) is non pyrophosphorolytic, in contrast to reaction a). 



Bacteria, yeast, and many animal tissues also contain the enzyme galactowaldenase 

 thereby providing a third mechanism for generating UDP galactose: 



galactowaldenase 

 1) UDP-galactose ' r UDP-glucose 



Mammary gland tissue from lactating rats and brain tissue from 2-3 week old rats contain 

 galactowaldenase and the P-P uridyl transferase (reaction 73, Table 4, p. 35) but not GP- 

 uridyl transferase. The livers from these animals contained all three enzymes. Galacto- 

 waldenase has been purified from liver. DPN* is required, suggesting that the inversion 

 at carbon 4 occurs by an oxidation and subsequent reduction of the carbohydrate (Maxwell, 

 1956). 



Literature p. 124 



