Protein conformation monitored by energy-selective optical spectroscopy.

Fluctuations in the polypeptide chain lead to disorder in proteins and to a distribution in the parameters that regulate their functions. Using low temperature (to reduce the fluctuations) and narrow-band lasers (to select one substate among the many forms), high-resolution absorption and fluorescence spectra for chromophores in proteins can be obtained. These spectra reveal information on the kind and extent of disorder in proteins and allow for the determination of the vibrational energies of both ground and excited state molecules, true inhomogeneous spectral width, and kinetic studies of individual protein substates.