Femtosecond transient absorption spectroscopy to study the effects of low irradiance light on cytochrome c and cytochrome c reductase

Abstract

Photobiomodulation (PBM) describes the enhancement of cellular functions following exposure to low irradiance visible or NIR light. Although these effects are not well understood, PBM has been shown to enhance the synthesis of ATP so the mitochondrion is the hypothesized target for the processes of photobiomodulation. More specifically, cytochromecontaining enzyme complexes of the electron transport chain (ETC) in the mitochondria are expected to be the primary photoabsorbers of the light thought to induce PBM. Recently, our group found light-induced changes in the activity of complex III (cytochrome c reductase) in isolated mitochondria. In this study, we use femtosecond transient absorption spectroscopy (TAS) to study the excited state dynamics of the electronic transitions in complex III as well as reduced cytochrome c. To investigate the potential for inducing PBM effects in these proteins, TAS experiments are performed without, and with, low irradiance light exposures during the scanning procedure choosing from blue (450 nm), red (635 nm), and near-infrared (808 nm) laser diodes. The TAS experiments with and without light exposures during the procedure are compared to determine if PBM effects were induced. Understanding illumination induced changes in the excited state dynamics of proteins can help to better characterize the molecular processes caused by PBM and lead to a more optimized treatment for the enhancement of human performance and therapy.