Mammalian complex III heme dynamics studied with pump-probe spectroscopy and red light illuminations

Area of Science:

• Biophysics
• Cellular Mechanisms
• Spectroscopy

Background:

• Photobiomodulation (PBM) mechanisms remain unclear.
• Understanding PBM requires studying molecular interactions with light.
• Complex III (C-III) is a key component of the electron transport chain.

Purpose of the Study:

• To investigate the effect of red light on the heme dynamics of porcine C-III.
• To determine if continuous wave laser coupled transient absorption spectroscopy (CW-TAS) can detect PBM effects.
• To elucidate the molecular mechanisms of PBM initiation.

Main Methods:

• Characterization of porcine C-III using transient absorption spectroscopy (TAS).
• Application of a novel continuous wave laser coupled TAS (CW-TAS) procedure.
• Analysis of heme dynamics in the c1 reduced state of C-III under red light (635 nm, 4.7 mW/cm2).

Main Results:

• Vibrational cooling time constant for the oxidized state: 3.3 ± 0.3 ps.
• Axial ligand rebinding time constant for the c1 reduced state: 4.9 ± 0.4 ps.
• No significant changes in C-III heme dynamics were observed using CW-TAS.

Conclusions:

• The applied red light (635 nm, 4.7 mW/cm2) does not induce photobiomodulation (PBM) effects on C-III heme dynamics.
• Photodissociation of the axial ligand of C-III is not a mechanism for PBM initiation under these conditions.
• Further research is needed to fully understand PBM initiation mechanisms.