RESONANCE RAMAN LABELS AND RAMAN LABELS

Resonance Raman labels are small chromophoric molecules that are place d at biological sites as resonance Raman reporter groups. The label ma y resemble closely a natural biological component, or it may have no b iological counterpart and be placed at the site simply to probe the pr operties of that site. Most of the early work with resonance Raman lab els involved ligands binding to proteins, for example chromophoric sub strates or inhibitors binding to enzyme active sites. The sensitivity of Raman instrumentation has increased greatly in recent years such th at it no longer necessary to use the resonance condition to obtain the Raman spectrum of a ligand binding to a macromolecule. These data can now be obtained from non-resonance spectra by Raman difference spectr oscopy. It is still. advantageous if the ligand is a strong Raman scat terer and then the label becomes simply a Raman label. The advantages and disadvantages of resonance and non-resonance labels are discussed. For the latter, critical advantages of operating under non-resonance conditions and using deep red excitation are that problems associated with photochemistry and fluorescence interference are avoided; consequ ently a wide range of biochemical systems become accessible to Raman a nalysis. (C) 1998 John Wiley & Sons, Ltd.