70 research outputs found
Random Walks on a Fluctuating Lattice: A Renormalization Group Approach Applied in One Dimension
We study the problem of a random walk on a lattice in which bonds connecting
nearest neighbor sites open and close randomly in time, a situation often
encountered in fluctuating media. We present a simple renormalization group
technique to solve for the effective diffusive behavior at long times. For
one-dimensional lattices we obtain better quantitative agreement with
simulation data than earlier effective medium results. Our technique works in
principle in any dimension, although the amount of computation required rises
with dimensionality of the lattice.Comment: PostScript file including 2 figures, total 15 pages, 8 other figures
obtainable by mail from D.L. Stei
Diffractive optics-based heterodyne-detected four-wave mixing signals of protein motion: From “protein quakes” to ligand escape for myoglobin
Ligand transport through myoglobin (Mb) has been observed by using optically heterodyne-detected transient grating spectroscopy. Experimental implementation using diffractive optics has provided unprecedented sensitivity for the study of protein motions by enabling the passive phase locking of the four beams that constitute the experiment, and an unambiguous separation of the Real and Imaginary parts of the signal. Ligand photodissociation of carboxymyoglobin (MbCO) induces a sequence of events involving the relaxation of the protein structure to accommodate ligand escape. These motions show up in the Real part of the signal. The ligand (CO) transport process involves an initial, small amplitude, change in volume, reflecting the transit time of the ligand through the protein, followed by a significantly larger volume change with ligand escape to the surrounding water. The latter process is well described by a single exponential process of 725 ± 15 ns at room temperature. The overall dynamics provide a distinctive signature that can be understood in the context of segmental protein fluctuations that aid ligand escape via a few specific cavities, and they suggest the existence of discrete escape pathways
- …