Ureides metabolism

In an earlier report (J>), the decay of healthy yam tubers during storage was shown to be a result of catabolism of its proteins by an active a-glutamyl transpeptidase. There is also some alkaline proteolytic activity in the yam tuber (6), but little information is available on individual enzymes of the purine degradative pathway and on the properties of an alkaline proteinase that may function in yams during storage. This report describes the interrelation of five enzymes of ureide metabolism in fresh and stored yams, the release of ammonia in vitro by three of the enzymes that may provide an environment for alkaline proteinase activity in vivo, and the in vitro properties of an... 

Release of Ammonia. Of the five enzymes, three lead to release of amide/ami no nitrogen as ammonia during ureide metabolism ... 

Alkaline Proteinase Activity in Yams. The release of ammonia at several stages during ureide metabolism suggested a potential for alkaline conditions in yam tubers, rather than the usual neutral or acid conditions generally found in seeds and plants. 

Schutte, M. Luckner, eds.). Deutscher Verlag der Wissenschaften, Berlin 1985 Thomas, R. J., Schrader, L. E. Ureide metabolism in higher plants. Phytochemistry 20, 361-371 (1981)... 

Daily, the two enzymes have quite distinct electrophoretic mobilities and immunological properties. Levels of leaf urease were calculated to be adequate for known flux rates for ureide metabolism. Polacco et al. (1985) speculated that this ubiquitous urease might play a role in ureide catabolism. 

Ureides. Compounds that contain urea functionalities are stable and are not commonly metabolized or hydrolyzed. 

Ammonium, the primary product of nitrogen fixation, is transported to the host cell cytoplasm where it is assimilated into amides and, in some cases, further converted into ureides before being transported to the shoot. Since the physiological environment within the nodule is apparently different from the other parts of the plant, nodule-specific or nodule-abundant forms of several enzymes of the nitrogen and carbon assimilation pathways have evolved, and are induced to improve the efficiency of nitrogen and carbon metabolism in nodules. 

From their discovery, the glycosyl ureides have been of interest from a biochemical standpoint. The fact that D-glucose and urea occur in human blood in approximately equimolar concentrations (about 0.006 M) has led to speculation and to some investigation of the metabolic role of these compounds. Mayer, in a series of metabolic experiments with dogs, attempted to determine whether 1-D-glucosylurea is a natural constituent of normal or of pathological blood or urine. 

Whether the glycosyl ureides play a role in normal metabolic processes remains a challenging question. The fact that the chemical synthesis of pyrimidine nucleosides from glycosyl ureides has been demonstrated should serve to stimulate further investigation of this problem, particularly with the application of some of the more recent, sensitive techniques including radioactive tracers and paper chromatography. ... 

Balance sheets for production, storage, and utilization of ureides have been constructed for different stages of development of the nodulated cowpea (Herridge et al., 1978). In practically all periods of growth the shoot metabolized over 90% of the ureides it received from the roots, which acted as a N source for protein synthesis. During early fruit development when N... 

Ureides are metabolized by conversion to urea and glyoxylate as shown in Fig. 6. Allantoin may be hydrolyzed to allantoic acid as discussed above. The key enzyme in the breakdown is allantoicase, which is located in the shoots and pods (Tajimaet al., 1977). Such a system allows for the transport of N from the nodule to the shoot and rapid metabolism of the ureides to liberate N for protein synthesis (Herridge et al., 1978). 

Figure 2A,B, C show the typical HPLC of DNPH of urinary carbonyls. The Maillard reactants such as acetone, methylglyoxal, glyoxal, crotonal, were tentatively identified among these peaks, because identification was based only on retention times of HPLC (data not shown). Figure 2 shows that there were marked qualitative and quantitative differences of urinary carbonyls by each individual. Since urine is an ultra filtrate of plasma, many factors in urine are present. Therefore, our present findings of urinary carbonyl ureides would serve as the useful guide for the discovery of novel diagnostic markers for abnormal metabolisms.

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