Related Experiment Video
Updated: Sep 13, 2026

A Fluorescence Fluctuation Spectroscopy Assay of Protein-Protein Interactions at Cell-Cell Contacts
Published on: December 1, 2018
A spectroscopic technique for measuring slow rotational diffusion of macromolecules. 2: Determination of rotational
Abstract:
Experiments have been performed to test the validity of measurements of slow rotational diffusion using eosin isothiocyanate as a probe. When eosin-protein conjugates are covalently bound to Sepharose 4B, the dichroism of the flash-induced absorption transient does not decay with time. The magnitude of the dichroism is smaller than for eosin in solid solution. These results, together with measurements with highly viscous solutions, demonstrate the existence of a rapid but restricted independent motion of the eosin probe. This causes a partial loss of pf dochroism leaving a residual dichroism whose time dependence is determined by the rotational motion of the protein. Rotational correlation times in the microsecond-millisecond time range have been determined for eosinprotein conjugates dissolved in glycerol-water mixtures of varying viscosity. The measured values are in good agreement with theoretical predictions and show the correct dependence on the viscosity of the medium and the size and state of association of the protein.
Related Concept Videos
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
Two-Dimensional (2D) NMR: Overview
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse.
Protein Dynamics in Living Cells
Fluorescent recovery after photobleaching (FRAP) is a fluorescent-protein-based detection technique used to quantify protein movement rates within the cell. This method exposes a small portion of the cell to an intense laser beam. The laser beam causes permanent photobleaching of the fluorophore-tagged proteins in the exposed region. As the bleached...
Atomic Nuclei: Types of Nuclear Relaxation
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers energy to a nearby...
2D NMR: Overview of Homonuclear Correlation Techniques
COSY90 is the standard two-dimensional (2D) COSY experiment that...
2D NMR: Overview of Heteronuclear Correlation Techniques

