Protein diffusion probed by the transient grating method with a new type of photochromic molecule.

A new type of photochromic molecule that can be used for diffusion coefficient (D) measurements of various proteins in solution is described. The absorption spectrum of this molecule is changed upon photoexcitation by the trans-cis isomerization reaction. Target proteins were labeled by this photochromic molecule in the dark and the translational motion of the proteins was detected by the transient grating (TG) method. The TG signal was simple enough to determine D accurately and was stable even for long-time irradiation by the laser light. The TG method using this probe molecule improves many drawbacks of the other techniques.