Glutamine transport compound

Asparagine and glutamine are the major transport compounds found in plants, with arginine frequently being present particularly in perennials (e.g., trees). Nonprotein amino acids, homoserine, canavanine, and y-methy-leneglutamine are utilized in specific plants. The ureides allantoin and allantoic acid are frequently found in nodulated tropical legumes. 

FIGURE 31-7 Mitochondrial carriers. Ions and small molecules enter the intermembrane space, since the outer mitochondrial membrane is not a significant permeability barrier. However, the inner mitochondrial membrane is impermeable to ions except those for which there are specific carriers. Most of the carriers are reversible, as indicated by two-headed arrows. Compounds transported in one direction are indicated in red. The ATP/ADP translocase and the aspartate-glutamate carrier are both electrophoretic their transport is driven in the direction of the mitochondrial membrane potential, as indicated by red arrows. Glutamine is carried into the matrix by an electroneutral carrier. The unimpaired functioning of mitochondrial carriers is essential for normal metabolism. (Adapted with permission from reference [70].)... 

Figure 3 Correlation between the fraction absorbed and the membrane permeability in Caco-2 cells. Papp represents the membrane permeability of following 20 compounds, and was obtained by measuring the transcellular transport from the apical-to-basal side in Caco-2 cells. The fraction absorbed was obtained from literature. A amoxicillin, B antipyrine, C atenolol, D caffein, E cephalexin, F cyclosporin A, G enalaprilate, H L-glutamine, I hydrocortisone, J inulin, K D-mannitol, L metoprolol, M L-phenylalanine, N PEG-400, O PEG-4000, P propranolol, Q sucrose, R taurocholate, S terbutaline, T testosterone. Source From Ref. 37.

The amount of N fertilizer applied to the roots of the plant also affects the amount and ratio of compounds transported increased amounts of NO3 applied to wheat increased the total amount of N transported in the xylem and also the proportion of NOj-N amino-N (Kirkman and Miflin, 1979). In maize xylem exudates (Ivanko and Ingversen, 1971) over 10-fold less N is transported in plants starved for 5 days. On the addition of NO3 to the plants the N content of the sap increased rapidly after 4 h. The addition of NHJ to the roots causes a rapid synthesis of the two amides glutamine and asparagine, presumably as a detoxification mechanism. 

It has been clearly demonstrated that only a limited number of compounds are utilized for N transport in higher plants. By far the most common compounds are the amides asparagine and glutamine and to a lesser extent the ureides. Canavanine and the various substituted amides are only found in a very small number of species. 

Other reactions of glutamine include participation in purine biosynthesis and transpeptidation. This compound seems to be important in transport of ammonia, and much of the glutamate of proteins bears a 7-amide. These considerations and the transaminations of glutamine make the synthesis and reactions of this compound of considerable biological interest. 

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