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Interactions between Ca2+ and the Asp side chains in the Ca2+-binding site of equine lysozyme were investigated by Fourier-transform infrared (FT-IR) spectroscopy. In the spectrum of equine lysozyme, the intensities of the bands at about 1595 cm-1 and 1578 cm-1 in the region of the COO antisymmetric stretches increased upon Ca2+ binding. In the region of the COO- symmetric stretches, the loss of intensity at about 1388 cm-1 and gains of intensities at about 1423 cm-1 and 1403 cm-1 were observed due to Ca2+ binding to equine lysozyme. The spectral changes for equine lysozyme indicate that the COO- groups of Asp85, Asp90 and Asp91 in the Ca2+-binding site coordinate to Ca2+ in the pseudo-bridging mode, where divalent metal cation is bound to one of the two oxygens in the COO- group and a water molecule is hydrogen bonded to the other oxygen. The results presented here provide further evidence for a high degree of similarity between Ca2+-binding lysozyme and alpha-lactalbumin. The effects of Ca2+ binding on the main-chain conformation of equine lysozyme were compared with those of bovine alpha-lactalbumin and hen egg-white lysozyme.

Side chain dynamics of right-handed α-helical poly(γ-benzyl L -glutamate) (PBLG) was investigated by solid state 2 H NMR. Two main motional modes composed of the large amplitude motions and the rapid and small-amplitude librations along the side chain were extracted from line shapes and T 1 data above the glass-like transition temperature. The motional correlation times and amplitudes of the former are widely distributed, showing the heterogeneity of the side chain region. The phenyl rings at the end of the side chain also undergoes π-flipping. This reorientation is slightly restricted in the racemic complex of PBLG and its enantiomer, left-handed α-helical poly(γ-benzyl D -glutamate), in which phenyl rings from each L and D polymer are considered to stack regularly. The large amplitude motions and the librations are rather restricted in the stack state. About 75% of the side chain participate in the stacking. It is noted that the stacking structure is very flexible on the NMR time scale and the model for the ‘static’ stacks of the phenyl rings should be modified.