Nitrogen transport asparagine

Important concentrations of aspartic add and asparagine are observed these amino acids are known to be the more common form of nitrogen transport or stocking for plants, alga, etc., [17 ]. 

Two amino acids—asparagine and glutamine—contain acid-amide groups in the side chains, from which NH3 can be released by hydrolysis (hydrolytic deamination). In the blood, glutamine is the most important transport molecule for amino nitrogen. Hydrolytic deamination of glutamine in the liver also supplies the urea cycle with NH3. 

Most green plants transport nitrogen from roots to growing shoots as asparagine. However, in peanuts P-methyleneaspartate is the major nitrogen carri-er, °° and in some legumes, including soybeans, allantoin and allantoate (Eq. 24-15) play this role. Allantoin arises from hydrolysis of purines (see Fig. 

A similar classification may be appropriate for N2-fixing actinorhizal species. Asparagine is the major product of N2 fixation in Myiica species (32), w hereas the ureide, citrulline, predominates in Alnus species (20, 33). The structures of the difiFerent nitrogenous components transported from N2-fixing plants are given in Figure 3. 

Transport and Metabolism of Asparagine and Other Nitrogen Compounds within the Plant... 

In conclusion there is little doubt that cyanide can be converted to asparagine. It must be assumed that an active defense mechanism has evolved to prevent the accumulation of cyanide even at very low levels. If the localization of -cyanoalanine synthase in the mitochondria is correct then the protection of the sensitive electron transport chain is enhanced. The suggestion that the cyanide pathway contributes a major source of carbon and nitrogen to the synthesis of asparagine is doubtful. 

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). 

---