Artificial cells containing urease glutamate dehydrogenase and glucose6phosphate dehydrogenase

Since the needed NADH can be recycled, the next study was to see whether we could use a multienzyme system for the removal of urea. First, we used a model system of polymer membrane artificial cells loaded with three enzymes: urease, glutamate dehydrogenase and glucose-6-phosphate dehydrogenase (Fig. 11.13) (Cousineau and Chang, 1977; Chang and Malouf, 1979; Chang etal., 1979b). Urease converts urea into ammonia. Then glutamate dehydrogenase converts

6-phosphogluconate

Fig. 11.13. Polymer membrane artificial cells containing urease, glutamate dehydrogenase, glucose-6-phosphate dehydrogenase for the multistep enzyme reaction of conversion of urea into amino acid glutamic acid and for the recyling of NADPH. Urea is lowered without any increase in ammonia level, as ammonia is converted into glutamate (Cousineau and Chang, 1977; Chang and Malouf, 1979; Chang et al., 1979b).

6-phosphogluconate

Fig. 11.13. Polymer membrane artificial cells containing urease, glutamate dehydrogenase, glucose-6-phosphate dehydrogenase for the multistep enzyme reaction of conversion of urea into amino acid glutamic acid and for the recyling of NADPH. Urea is lowered without any increase in ammonia level, as ammonia is converted into glutamate (Cousineau and Chang, 1977; Chang and Malouf, 1979; Chang et al., 1979b).

TIME (mins)

ammonia into glutamic acid. Glucose-6-P dehydrogenase serves to recycle of NADPH.

The rate of conversion of urea into glutamate and the recycling of NADPH could be followed by the rate of formation of 6-phosphogluconate, decrease in urea level, or the formation of glutamic acid. Ammonium acetate could be used in this reaction instead of urea. Figure 11.13 shows that the area level is lowered without any increase in ammonia level, as ammonia is efficiently converted into glutamate. Glutamate is formed at the same rate irrespective of whether urea or ammonium acetate is used as the substrate. This suggests that the rate-limiting step in this sequential reaction is in the conversion of ammonia into glutamic acid.

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