Phosphoribosyl pyrophosphate synthase

During the conversion of anthranilate to tryptophan, two additional carbon atoms must be incorporated to form the indole ring. These are derived from phosphoribosyl pyrophosphate (PRPP) which is formed from ribose 5-phosphate by transfer of a pyro-phospho group from ATP.60 61 The - OH group on the anomeric carbon of the ribose phosphate displaces AMP by attack on Pp of ATP (Eq. 25-5). In many organisms the enzyme that catalyzes this reaction is fused to subunit II of anthranilate synthase.62 PRPP is also the donor of phosphoribosyl groups for biosynthesis of histidine (Fig. 25-13) and of nucleotides (Figs. 

Anthranilic acid is the precursor to the amino acid tryptophan via the attachment of phosphoribosyl pyrophosphate to the amine group to form A-(5 -phosphoribosyl)-anthranilate (PRA) (Fig. 14.5) [11]. The second step of the tryptophan biosynthesis is the PRA isomerization to l-(o-carboxyphe-nylamino)-l-desoxyribuoso-5-phosphate (CdRP) by PRA isomerase. Further elimination of hydroxyl group and decarboxylation forms indole-3-glycerol phosphate (InGP) by InGP synthase. Tryptophan synthase catalyzes the final two... 

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