Browsing by Author "Cao, Hung Duc"

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    A quasi-elastic neutron scattering study of hydrogen dynamics in trypsin-deuterium oxide solution (deuterium oxide)
    (1993) Cao, Hung Duc; Rorschach, Harold E., Jr.
    The quasi-elastic neutron scattering (QNS) method is a useful technique to study biomolecular dynamics. The versatility of the method makes possible motional studies of biomolecules in different forms: powder, crystalline, and solution; and at different temperatures. Thus, it allows investigation of biomolecular dynamics in different states of matter. We have used the QNS method to study the motion of the trypsin chain segments in powder and in D$\sb2$O solution at temperatures of 200K, 280K, and 300K. The scattering spectra S(Q,$\omega$) were measured in constant-Q mode. The S(Q,$\omega$) for trypsin protons in liquid solution exhibits a broadening due to diffusive motion which is absent in the powder and the frozen solution. This diffusive motion has the character of a jump diffusion. The high-frequency thermal motion obtained from the Debye-Waller factor $\langle$u$\sp2\rangle$/3 $\cong$ 0.33A$\sp2$ at T = 300K is consistent with earlier measurements. The DW factor at lower temperatures for trypsin solution shows deviation from theoretical predictions.
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    Protein dynamics at various hydration levels using the incoherent quasielastic neutron scattering technique
    (1995) Cao, Hung Duc; Huang, Huey W.
    The incoherent quasi-elastic neutron scattering (IQNS) method is a useful technique to study biomolecular dynamics. The versatility of the method makes possible motional studies of biomolecules in different forms: powder, crystal, and solution; and at different temperatures. Thus, it allows for the investigation of biomolecular dynamics over a wide-range of physical conditions. We have used the IQNS method to study the motions of side chains in trypsin and myoglobin at various D$\sb2$O hydration levels. The scattering spectra S(Q,$\omega$) were measured in constant-Q mode. The protein in powder form exhibits vibrational high-frequency motions, while the protein in solution and in crystals are characterized by diffusive jumps, and high-frequency vibrations. At temperatures below 200K, the S(Q,$\omega$) for these proteins in solution is similar to an harmonic solid. As temperature increases, a transition is seen at 200K, above which the protein becomes more liquid-like with rapid transitions between conformational substates. The diffusion constant D for the side chains is on the order of 10$\sp{-6}$ cm$\sp2$/sec.