x1 = PRPP
x2 = IMP
x3 = SAMP
x4 = ATP
x5 = SAM
x6 = Ade
x7 = XMP
x8 = GTP
x9 = dATP
x10 = dGTP
x11 = RNA
x12 = DNA
x13 = HX
x14 = Xa
x15 = Gua
x16 = UA
x17 = R5P
x18 = Pi