Abstract
A Resonance Raman label, which is a submolecular probe for interactions in biochemical and biological systems, can provide a detailed vibrational spectrum from a specially designed chromophore when it is bound to a biochemically active site. The resonance Raman label technique was introduced by Carey et al. in 1972. Since then the technique has been applied to systems where time-dependent effects are not observed, such as enzymeinhibitor, antibody-hapten, and drug-receptor interactions. Recently the application of this method has been extended to enzyme-substrate reactions. The first example of enzyme- substrate reactions discussed in this review includes a cinnamoyl group in the active site as a resonance Raman probe. The resonance Raman spectrum of 4-amino-3-nitro cinnamoylpapain was totally distinct from that of the substrate or the product. Comarison of the spectrum of the enzyme-substrate intermediate with the spectra of model compounds revealed that there is a highly polarized π-electron system in the active site binding the acyl group. The second example of enzyme-substrate reactions uses dithio chromophore as a resonance Raman probe. The resonance Raman spectrum of dithioacylpapain enabled us to monitor the vibrational spectrum of the bonds undergoing catalytic transformation in the active site. The study. revealed that the effect of the active site is to select, from a mixture of at least two thermodynamically accessible states, the single conformer in which an intramolecular interaction is occurring within the acyl group.
