FACILE CHARACTERIZATION OF THE SPECTRA OF cis AND trans PHOTOISOMERS IN A MIXTURE OF ACYL‐ENZYMES BY RAMAN DIFFERENCE SPECTROSCOPY

Abstract Raman difference spectroscopy is used to provide the spectra of both the cis and trans forms of acryloyl‐based acyl enzymes from a mixture without resorting to purification. A mixture of cis and trans, about the‐C=C‐C(=O) ethylenic linkage, is generated photochemically and by subtracting the Raman spectrum of the mixture from the spectrum of the pure trans form prior to photochemical irradiation, Raman peaks of the trans acyl‐enzyme appear as “negative” features and of the cis form appear as “positive” features. No operator intervention is required to scale the spectra for subtraction, and thus information on the relative Raman scattering efficiencies of the cis and trans isomers can be obtained immediately from the data. Results for 5‐methylthienylacryloyl chymotrypsin confirm earlier data for the purified cis and trans forms and data for cis indoleacryloyl chymotrypsin are presented for the first time.