Efforts toward the direct experimental characterization of enzyme microenvironments: tyrosine100 in dihydrofolate reductase.

State secrets: Site-specific deuteration and FTIR studies reveal that Tyr100 in dihydrofolate reductase plays an important role in catalysis, with a strong electrostatic coupling occurring between Tyr100 and the charge that develops in the hydride-transfer transition state (see picture, NADP(+) purple, Tyr100 green). However, relaying correlated motions that facilitate catalysis from distal sites of the protein to the hydride donor may also be involved.