Quasielastic neutron and light-scattering techniques along with molecular dynamics simulations were employed to study the influence of hydration on the internal dynamics of lysozyme. We identified three major relaxation processes that contribute to the observed dynamics in the picosecond to nanosecond time range: 1), fluctuations of methyl groups; 2), fast picosecond relaxation; and 3), a slow relaxation process. A low-temperature onset of anharmonicity at T ; 100 K is ascribed to methyl-group dynamics that is not sensitive to hydration level. The increase of hydration level seems to first increase the fast relaxation process and then activate the slow relaxation process at h ; 0.2. The quasielastic scattering intensity associated with the slow process increases sharply with an increase of hydration to above h ; 0.2. Activation of the slow process is responsible for the dynamical transition at T ; 200 K. The dependence of the slow process on hydration correlates with the hydration dependence of the enzymatic activity of lysozyme, whereas the dependence of the fast process seems to correlate with the hydration dependence of hydrogen exchange of lysozyme.

Two onsets of anharmonicity are observed in the dynamics of the protein lysozyme. One at T approximately 100 K appears in all samples regardless of hydration level and is consistent with methyl group rotation. The second, the well-known dynamical transition at T approximately 200-230 K, is only observed at a hydration level h greater than approximately 0.2 and is ascribed to the activation of an additional relaxation process. Its variation with hydration correlates well with variations of catalytic activity suggesting that the relaxation process is directly related to the activation of modes required for protein function.

Positron annihilation lifetime spectroscopy is a powerful method for characterizing free volumes in a variety of materials. Correlations between positron annihilation rates and the size of free-volume regions in which o-Ps localizes are well described. Unfortunately, difficulties in the analysis of positron annihilation lifetime data have limited the approach to the determination of average lifetimes and average free volumes. Recent advances in the development of numerical integral transform methods now make it possible to extract continuous distributions of positron annihilation rates. The application of these methods to the determination of free-volume distributions is described. The variable transformations required to convert positron annihilation rate probability density functions (PDF) to the corresponding lifetime, radius, and free-volume PDFs are given and the approach is illustrated by application to positron annihilation lifetime data for amorphous polytetrafluoroethylene.

Mitochondrial dysfunction has been proposed to play a role in the neuropathology of multiple sclerosis (MS). Previously, we reported significant alterations in the transcription of nuclear-encoded electron transport chain genes in MS and confirmed translational alterations for components of Complexes I and III that resulted in reductions in their activity. To more thoroughly and efficiently elucidate potential alterations in the expression of mitochondrial and related proteins, we have characterized the mitochondrial proteome in postmortem MS and control cortex using Surface-Enhanced Laser Desorption Ionization Time of Flight Mass Spectrometry (SELDI-TOF-MS). Using principal component analysis (PCA) and hierarchical clustering techniques we were able to analyze the differential patterns of SELDI-TOF spectra to reveal clusters of peaks which distinguished MS from control samples. Four proteins in particular were responsible for distinguishing disease from control. Peptide fingerprint mapping unambiguously identified these differentially expressed proteins. Three proteins identified are involved in respiration including cytochrome c oxidase subunit 5b (COX5b), the brain specific isozyme of creatine kinase, and hemoglobin β-chain. The fourth protein identified was myelin basic protein (MBP). We then investigated whether these alterations were consistent in the experimental autoimmune encephalomyelitis (EAE) mouse model of MS. We found that MBP was similarly altered in EAE but the respiratory proteins were not. These data indicate that while the EAE mouse model may mimic aspects of MS neuropathology which result from inflammatory demyelinating events, there is another distinct mechanism involved in mitochondrial dysfunction in gray matter in MS which is not modeled in EAE.

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