TREHALOSE PREVENTS MYOGLOBIN COLLAPSE AND PRESERVES ITS INTERNAL MOBILITY

A quantitative model, which involves diffusion on a temperature-depend ent potential, is utilized to analyze the time-dependence of geminate CO recombination to sperm whale myoglobin in a trehalose glass and the accompanying spectral shifts. Most of the recombination is inhomogene ous. This is due to higher geminate reactivity rather than slower prot ein relaxation. A fraction of the hemes undergoes relaxation with a co ncomitant increase in the barrier height for recombination. The activa tion energy for conformational diffusion (relaxation) is considerably lower than in glycerol/water. ''Protein collapse'', manifested in glyc erol/water by a decrease in the equilibrium conformational separation between the bound and deoxy states, is completely prevented in trehalo se. We postulate that the high internal viscosity in glycerol/water is due to dehydration of the heme pocket. Trehalose prevents the escape of the few vital internal water molecules and thus preserves the inter nal lability of the protein. This might be important in understanding the ability of trehalose to protect against the adverse effects of deh ydration.