ABSTRACT
A challenge in the life sciences today is understanding processes in living organ isms at the molecular level. A deeper insight into these processes enables progress in medicine and biotechnology. The two essential players at the molecular levels are DNA and proteins (1). DNA stores the genetic information. Proteins are the nanomachines that perform the biochemical processes of living organisms. Un derstanding biological processes at the molecular level therefore means un derstanding the function of proteins at the atomic level. An essential step in the elucidation of the functioning of a protein is the determination of its threedimensional structure. Structural models of proteins are provided today almost routinely by x-ray structure analysis and for smaller water-soluble proteins by NMR spectroscopy (2,3)- However, both techniques usually deliver structural models of the quiescent protein ground state. Understanding how proteins func tion needs in addition time-resolving techniques to determine transient occupied states with atomic resolution. Spectroscopic techniques fulfill both conditions (4). Infrared spectroscopy especially is capable of monitoring absorption bands of single molecular groups of a protein and their absorbance changes down to femto second time resolution. Time-resolved Fourier transform infrared (FT-IR) differ ence spectroscopy has proved itself as a powerful method for studies of molecular reaction mechanisms of proteins larger than 100,000 daltons and time resolutions
up to nanoseconds (5). Using monochromatic IR spectroscopy, the time resolu tion is even pushed into the picosecond time range (6). However, dispersive tech niques provide absorbance changes only at selected single wavenumbers, but not complete spectra as does the polychromatic FT-IR technique. In order to assign bands, which is important for interpretation, complete spectra are needed. In addi tion, pulsed IR sources in combination with the FT-IR technique will allow moni toring even in the picosecond time range in the future.
