Low frequency dynamics of chymotrypsin by neutron spectroscopy

Abstract

ABSTRACT:The low frequency vibrational modes of enzymes have large amplitudes of vibration which should be related to conformational changes that occur during enzyme action. In the present paper we present inelastic neutron scattering measurements for a-chymotrypsin that show a peak in the low frequency spectrum. This peak is well defined at 77 K. Gaussian fits yield values of 0.93 -+ 0.05, 0.86 +-0.04, 0.81 _+ 0.05, and 0.87 -+ 0.06 THz for the peak position at wave vector transfers (Q) of 1.00, 1.40, 1.85, and 3.00 A.-1, respectively. The full widths at half maximum are all greater than the resolution (0.2 THz) by at least a factor of two. At 298 K a weak peak at about 0.6 THz was observed for Q values of 1.0, 1.4 and 1.85 A,-1. The data are interpreted in terms of the allowed oscillations of a large globular protein treated as an elastic sphere. Assuming a Raman active oscillation at 0.9 THz it is shown that a peak in the neutron scattering response at 0.6 THz may arise from a rotational shear mode of the chymotrypsin molecule.