LUIS F. LELOIR 



There is still another redox reaction of interest. This is the 

 oxidation at position 2 of a sugar alcohol, D-sorbitol, to the cor- 

 responding ketose, D-fructose, which was found to be catalyzed 

 by a liver enzyme with diphosphopyridine nucleotide as oxi- 

 dant (18). Since the reaction is reversible, it appears likely that 

 polyhydric alcohols are formed in plants by reduction of ketoses. 



Amination 



Glucosamine is present in the acetylated and polymerized 

 form as chitin in the cell walls of fungi and in the shells of 

 Crustacea. Hyaluronic acid, a mixed polymer of glucosamine 

 and glucuronic acid, is present in vitreous humor, umbilical 

 cord, and synovial fluid, and is formed by some hemolytic 

 streptococci. Tracer evidence has shown that the carbon skele- 

 ton of glucosamine is derived directly from glucose without 

 breakage of the chain. Evidence from the enzymic side has 

 shown that extracts can be obtained (16) from Neurospora which 

 will catalyze the reaction 



hexose-6-phosphate + glutamine > 



glucosamine phosphate + glutamic acid (14) 



It may be pointed out that Neurospora was selected for this 

 study, not because it is an especially interesting organism, but 

 because it was believed that its glucosamine metabolism should 

 be high in order to supply the organism with the necessary ma- 

 terial for the building of its chitin walls. Following this assump- 

 tion, a fairly active enzyme was obtained from Neurospora, and 

 now that we know something about the reaction we can look for 

 it in other organisms. 



The enzyme has not been separated from the isomerase 

 which catalyzes the interconversion of glucose-6-phosphate into 

 fructose-6-phosphate, so that a discussion of the mechanism is 

 premature. It might be formulated as shown in reaction (15) 

 and would involve an exchange of an OH for an — NH2 group. 



600 



