Motions of single molecules and proteins in trehalose glass

The fluorescence intensity-time records of individual metal-free porphyrin cytochrome-c and Zn porphyrin cytochrome-c molecules whose translational motions are restricted by encapsulation in trehalose are examined by single-molecule spectroscopy by means of a two-channel confocal microscope that records transient fluorescence signals in two orthogonal polarization directions. Large angular motions often occur on time scales ranging to many seconds. Measurements of the photobleaching time distributions indicate that the trehalose glass restricts the accessibility of the fluorescent molecules to oxygen.