Raman Spectra of Isotope-substituted Mitochondria of Living Budding Yeast Cells: Possible Origin of the “Raman Spectroscopic Signature of Life”

The 13C and 2H isotope substitution effects have been examined for the “Raman spectroscopic signature of life,” a mitochondrial Raman band at 1602 cm−1 that sharply reflects the metabolic activity of living yeast cells. The band shifts to 1542 cm−1 with 13C substitution and to 1599 cm−1 with 2H substitution. Normal mode analysis based on a DFT calculation suggests that it originates from a C=C double bond having no hydrogen atoms attached to the carbon atoms. The in-phase C=C stretch mode of ubisemiquinone radicals (CoQ and/or CoQH•) emerges as a strong candidate for the origin of the 1602 cm−1 band.