Abstract

Time- and space-resolved Raman spectra of mitochondria in single living fission yeast cells have been measured under various nutrient, stress, and atmospheric conditions. A focus is placed on the behavior of the Raman band located at 1602 cm⁻¹, which sensitively reflects the metabolic activity in mitochondria and which has been called by us the "Raman spectroscopic signature of life". Addition of nutrients increases the intensity of this band by ∼1.5 times, confirming its correlation with the metabolic activity in mitochondria. The spectra of cells cultured under 100% N₂, 100% O₂, and N₂/O₂ (V_N2:V_O2 ≅ 4:1) atmospheres have been measured for both ¹⁶O₂ and ¹⁸O₂. Yeast cells have been found to lose their metabolic activity after the culture under 100% N₂ and 100% O₂ atmospheres. Cells cultured under a N₂/¹⁶O₂ (¹⁶O₂ = 20%) atmosphere show strong "Raman spectroscopic signature of life". No ¹⁸O isotopic shift has been found for the wavenumber 1602 cm⁻¹, indicating that the origin of this signature is neither O₂ nor an O-containing small molecule. Addition of H₂O₂ causes a quick decrease of the "Raman spectroscopic signature of life", followed by the cis–trans isomerization in the unsaturated phospholipid chain. The "Raman spectroscopic signature of life" has thus been proved to be a reliable real-time and in vivo indicator for monitoring the metabolic activity in living cells.

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