EXPERIMENTAL-DETERMINATION OF INTERNAL ELECTRIC-FIELDS IN ORDERED SYSTEMS - MYOGLOBIN AND CYTOCHROME-C

We have developed methods to determine internal molecular electric fie lds at the sites of probe molecules which were doped into various host matrices from the Stark effect on persistent spectral holes. These in ternal electric fields are of fundamental importance in charge separat ion and transfer processes especially in biological systems (e.g. phot osynthetic reaction center). Two Interesting systems to demonstrate th e potential of our methods are the globular proteins myoglobin and cyt ochrome C, both of which contain a heme (iron porphyrin) chromophore a s a suitable probe molecule. The porphyrin pi-electron system serves a s a detector for the two In-plane components of the internal electric field. The orientation and magnitude of the in-plane field provide str uctural information. We conclude that in myoglobin the dominant field sources are the deprotonated propionic acid side chains of the porphyr in, but that in cytochrome C additional field sources close to the por phyrin also contribute significantly.