sentences:  First, orotate phophoribosyltransferase has Aspartic acid- Aspartic acid residues next to its PRPP-binding motif which interact with the ribosyl 2-/3- hydroxyl groups that stabilize the movement of Carbon-1 of the bound ribosyl group.The stabilization occurs through a hydrogen bonding network of these hydroxyl groups with pyrophosphate, water and magnesium.Second, the side-chains of the C-terminal end of the PRPP-binding motif interact favorably with PRPP’s 5-phosphate.