Monophosphate IMP Is the First Purine Nucleotide Formed

Inosine Monophosphate (IMP) Is the First Purine Nucleotide Formed 

The pathway from PRPP to the first complete purine nucleotide, inosine monophosphate (IMP), involves 10 steps and is shown in figure 23.10. It would seem logical that the purine should be built up first, followed by addition of ri-bose-5-phosphate, but this is not the case. The starting point is PRPP, to which the imidazole ring is added the six-member ring is built up afterward. 

Step 1, in which phosphoribosylamine is formed, is catalyzed by glutamine phosphoribosylpyrophosphate ami- 

Absorption spectra of the common ribonucleoside-5 -monophosphates giving the maximum absorbance are as follows AMP, 15.4 x 103  

Synthesis of phosphoribosylpyrophosphate (PRPP). This is an unusual kinase-catalyzed reaction because the group transferred is the pyrophosphate group rather than the phosphate group. 

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