Effects on turkey erythrocyte P2Y1 receptor-mediated phosphoinositide metabolism by methanocarba nucleotide analogues (3). The two structural variations restrict the ring pucker, i.e. hold the ribose-like ring (pseudosugar) in either Northern (N) or Southern (S) envelope conformations. PLC response is indicated on the y-axis, either in the presence (for antagonist MRS 2279, ▲, or partial agonist MRS 2266, ●) or absence (for full agonist MRS 2268, ▽, or partial agonist MRS 2266, ○) of the agonist 2-MeSADP, 30 nM.