Amino acid residue 104 in an alpha-class glutathione S-transferase is essential for the high selectivity and specificity of the enzyme for 4-hydroxynonenal

By using resonance-enhanced two-photon ionization in a supersonic beam, photoionization spectra of the 0(0)0 band of the first singlet-singlet electronic transition of 35Cl-, 37Cl-, 79Br-, and 81Br-C6H5 have been obtained at a rotational temperature of 1 K. The ions have been analyzed according to their masses in a time-of-flight mass spectrometer. From the spectra of 35Cl- and 37Cl-C6H5 obtained simultaneously, an isotope shift of 0.14 +/- 0.02 cm-1 has been determined. Similarly, from the spectra of 79Br- and 81Br-C6H5 the isotope shift resulted to be smaller than 0.02 cm-1. The spectra obtained have been interpreted by considering the geometrical structure and symmetry of each molecule, and values for the rotational constants and geometrical parameters in the upper and lower states have been obtained in agreement with the experimental results.