FIGURE 5.

Relaxed-eyed steric pairs of the van der Waals surface of ribonuclease A. Those protein protons for which the oxygen-induced relaxation rate constant is <0.6 s⁻¹ are colored blue. (a) Gln-74:HB1 and Ile-107:HG11 (arrows) are located at a surface crevice surrounded by hydrophobic residues. An interpenetrating water network is reported in the neighborhood (Savage and Wlodawer, 1986; Wlodawer et al., 1988). (b) Ser-75:HB1 is the only surface proton with low oxygen-induced relaxation rate. Two of the invariant water molecules (W216 and W208) are found nearby (Sadasivan et al., 1998), which is consistent with the steric exclusion of oxygen caused by hydration effects.