Abstract

Picosecond polarization spectroscopies have been used to probe relaxation processes in heme proteins induced by ligand photodissociation. In particular, probing the N-band of myoglobin at 355 nm reveals a relaxation of several hundreds of picoseconds, over two orders of magnitude longer than the dynamics of photo-induced bond cleavage. Similar dynamics are also observed for studies in the Soret region. Time resolved linear dichroism studies confirm that the evolution of the CD signal does not arise from a change in the direction or degeneracies of the two degenerate, perpendicular transition moments of the heme. In addition, the time dependent spectral properties of the charge transfer absorption between the iron and the proximal histidine which results from photodissociation does not reveal any noticeable spectral shift on the time scale of the CD dynamics, strongly suggesting that the tilting of the proximal histidine is not causing the time dependent changes in the CD signal. These results suggest that the transient CD data is measuring a relaxation in the surrounding protein structure which is triggered by the photodissociation process.

© 1990 Optical Society of America