FIGURE 4.

A, motional models of leucine. Rotameric jumps around χ₁ and χ₂ angle are represented by four magnetically non-equivalent conformers (out of nine possible configurations) pointing toward the corners of a tetrahedron. White spheres correspond to the C^δ position, blue spheres correspond to C^γ, and black spheres are for C^β and C^α, the positions of which are not changed during the rotameric inter-conversions. B, valine. Rotameric jumps around the χ₁ angle are represented by three conformers. C, methionine. Arc motion mode (motions within rotameric potential) is used for all states and all temperatures. Rotameric motions mode involving only the χ₃ angle is used for the dry state at all temperatures and for the hydrated state at T < 250 K. For the hydrated state at T > 250 K, rotameric motions (involving in reality all three χ₁, χ₂, and χ₃ angles) are approximated by four artificial symmetrical conformers. Positions of the ²H labels at the methyl groups of the side chains are shown in red.