Asparagine, synthesis

Recombinant L-asparaginase depletion of aspargine a metabolic defect of asparagine synthesis in malignant cells which are dependent on an exogenous source of asparagine Fusion protein (TNFR Fc) competitive inhibitor of TNF... 

The formation of asparagine from aspartate is chemically analogous to the formation of glutamine from glutamate. Both transformations are amidation reactions and both are driven by the hydrolysis of ATP. The actual reactions are different, however. In bacteria, the reaction for the asparagine synthesis is... 

Tyrocidine C, C H N O,. Separation from the tyrocidine mixture Ruttenberg et al. Biochemistry 4, 11 (1965). Possesses same structure as tyrocidine B except that D-tryp -tophan replaces T>-phenylalanine attached to I.-asparagine. Synthesis Kuromizu, Izumiya. Tetrahedron Letters 1970,... 

It has been suggested that this pathway not only seems to supply the carbon skeletons for asparagine synthesis, but is also useful for reassimilating the large quantities of COg liberated in an actively fixing nodule (Christel-ler et al., 1977 Atkins et ai, 1978). Presumably C4 plants, which contain large amounts of the enzyme in the leaf mesophyll cells, are able to form aspartate for asparagine synthesis in a similar manner (for a comprehensive review see Hatch, 1978). 

Acetate has been used as a precursor for asparagine in a number of experiments on maize roots. The incorporation into asparagine in root tips is inhibited by sugars (Oaks and Johnson, 1970) and by azaserine and cy-cloheximide (Oaks and Johnson, 1973 Jones, 1977). Azaserine apparently has a dual action on asparagine synthesis, as it is a strong inhibitor of isolated AS from lupin cotyledons (Lea and Fowden, I975a,b), but in maize roots it inhibits the synthesis of the enzyme in vivo rather than acting as a direct inhibitor (Stulen and Oaks, 1977). 

For a time the cyanide pathway was considered the sole route of asparagine synthesis in plants. However a m jor drawback to the hypothesis is the lack of cyanide production in the majority of plant species. Oaks and Johnson (1972) showed that cysteine was a very poor precursor in the absence of cyanide, but upon the addition of 10 M KCN there was a rapid incorporation into asparagine. In confirmation Mead and Segal (1973) showed that in Acada georginae there was an enzyme that converted cys-... 

In 1980, Lea and Miflin discussed the transport and metabolism of asparagine and other nitrogen compounds within the plant. Since that time there have been major developments in the study of asparagine breakdown but the precise enzymology of asparagine synthesis in green leaves has still not been established (Sieciechowicz et al, 1988a). 

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