Table 1.

Summary of published EC50 values of ATP at P2X1, P2X2, and P2X4 receptors with alanine substitutions (and isoleucine in the case of P2X2F271I) of conserved residues and/or residues presumed to contribute to the ATP binding site

Corresponding residues in P2X1, P2X2, and P2X4P2X1P2X2P2X4Binding ofRegion
wt∼ 1 μma,b∼ 10 μmc∼ 3 μmd
*K68A, K69A, K67A∼ 1.4 mman.f.cn.f.ePhosphatebA
*K70A, K71A, K69A∼ 4 μma>1000 μmcn.d.A
*F185A, F183A, F185A∼ 9 μmbn.d.n.d.AdeninebB
*K190A, K188A, K190A∼ 4.3 μma>1000 μmc> 5000 μmdPhosphatedB
F230A, F227I, F230A∼ 1.3 μmbn.f.f> 5000 μmdAdenined
G278A, R275A, R278An.d.n.d.> 5000 μmdPhosphated
Y280A, D277A, D280An.d.n.d.> 5000 μmdMg2+d
N290A, N288A, N293A∼ 71 μmg∼1000 μmcn.d.(C)
*F291A, F289A, F294A∼ 140 μmbn.d.n.d.AdeninebC
*R292A, R290A, R295A∼ 71 μma>1000 μmcn.d.AdeninebC
*R305A, R304A, R309A∼ 3.7 μma>1000 μmcn.d.D
*K309A, K308A, K313A∼ 1.1 mman.f.c> 3000 μmhPhosphatebD