The first three enzymes of the pyrimidine pathway occur in the same cytosolic protein as a trifunctional protein or polyprotein (Table 14-2).
The initial letters of each enzyme activity of this trifunctionaI protein are combined to form the acronym CAD, and the protein is called the CAD complex.
The dehydrogenase, a protein with one activity, is located on the outer face of the inner mitochondrial membrane, where it can interact with cytosolic dihydroorotate.
The last two enzymes of the pathway occur in the cytosol as a bifunctional protein called UMP synthase (Table 14-2).
Besides its role in pyrimidine biosynthesis, the UMP synthase complex also catalyzes two reactions in the conversion of quinolinate, a tryptophan metabolite that resembles a pyrimidine, to NAD+ (see Figure 13-26).
These sequential reactions in NAD+ formation involve phosphoribosylation and decarboxylation.
The first three enzymes of the pyrimidine pathway occur in the same cytosolic protein as a trifunctional protein or polyprotein (Table 14-2).The initial letters of each enzyme activity of this trifunctionaI protein are combined to form the acronym CAD, and the protein is called the CAD complex.The dehydrogenase, a protein with one activity, is located on the outer face of the inner mitochondrial membrane, where it can interact with cytosolic dihydroorotate.The last two enzymes of the pathway occur in the cytosol as a bifunctional protein called UMP synthase (Table 14-2).Besides its role in pyrimidine biosynthesis, the UMP synthase complex also catalyzes two reactions in the conversion of quinolinate, a tryptophan metabolite that resembles a pyrimidine, to NAD+ (see Figure 13-26).These sequential reactions in NAD+ formation involve phosphoribosylation and decarboxylation.
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