IV INORGANIC N FIXATION AND TRANSFER 87 



Glucosamine-6-phosphate is required for the synthesis of hyahironic acid and 

 other amino polysaccharides. The synthesis of the gkicosamine moiety of hyaluronic 

 acid has been studied in Streptococcus hemolylicus (Lowther and Rogers, 1956). 

 Washed bacterial suspensions synthesize hyaluronate from glucose, provided that 

 glutamine or ammonium glutamate is present. Cell free extracts, however, require 

 glutamine rather than glutamate. In the presence of ammonium glutamate, 

 synthesis is much more sensitive to methionine sulfoxide than when glutamine is 

 added. Methionine sulfoxide inhibits glutamine synthesis from ammonia and 

 glutamate. The transfer of the amide group of glutamine in glucosamine synthesis 

 is also indicated by the fact that ^^NH, is incorporated efficiently into the glu- 

 cosamine of hyaluronate in the presence of a large pool of unlabelled glutamate. 



(5) Imidazole nitrogen of histidine. Experiments with glutamine-amide-'^N have 

 shown that in E. coli cells, the amide group of glutamine is a more efficient pre- 

 cursor of nitrogen i of the imidazole ring than NH,, glutamate, or asparagine 

 (Neidle and Waelsch, 1956). It is not known whether the amide group of glutamine 

 participates directly in histidine synthesis by primary formation of an amino sugar 

 or an amino aldehyde or indirectly by group transfer from an intermediate such 

 as guanine. The amide-nitrogen of glutamine also contributes to nitrogen 3 of the 

 imidazole ring, but less efficiently than to nitrogen i. Possibly, the a-amino 

 group of glutamate is the precursor of both nitrogen 3 of the imidazole ring and of 

 the a-amino group of histidine. 



5. Aspartic acid and the transfer of (f.- amino nitrogen 



Four reactions are now known involving the transfer of the alpha amino nitrogen 

 of aspartate. Mention has already been made of i ) the transamination reaction 

 with glutamic acid and, of 2) the condensation of aspartate with citrulline to form 

 argininosuccinic acid, the arginine precursor. The other two reactions are steps in 

 the synthesis of purine nucleotides. The first of these is the conversion of inosinic 

 acid to adenosine-5-phosphate. The reaction has been studied in yeast (Carter and 

 Cohen, 1955) E.coli (Lieberman, 1956) and bone marrow cells (Abrams and Bentley, 

 1955a, b, c). Adenylosuccinate is an intermediate in the conversion: 



i) Inosinic -r L-aspartate + GTP —> adenylosuccinate + GDP + Pi 



2) Adenylosuccinate — > adenosine-5-phosphate + fumarate 



It was shown with aspartate-^'*C and with inosinic acid-S-^'^C (Carter and 

 Cohen, 1955) that the former compounds are incorporated into adenylosuccinate 

 and into adenosine-5-phosphate without dilution of the radioisotope. It should 

 be noted that GTP is required in this process (Lieberman, 1956). The second 

 reaction is the synthesis of 5-amino-4-imidazole (N-succinyl carboxamide) ribotide 

 from amino-imidazole ribotide (AIR): (Lukens and Buchanan, 1956). 



ATP 



3) AIR + aspartate + HCO3" ► 5-amino-4-imidazole (N-succinyl-carboxamide) ribotide 



This reaction accounts for the fact that the nitrogen of aspartic acid is the source 

 of nitrogen i of the purine rings of adenylic and guanylic acids (Sonne et al., 1956; 



Literature p. 124 



