Low irradiance light exposure alters the activity of key enzymes in the mitochondrial electron transport chain

Abstract

Photobiomodulation (PBM) is an umbrella term for positive biological effects induced by low irradiance exposures of visible to near infrared light. Though therapeutic and protective benefits of PBM are increasingly well documented in the scientific literature, the molecular mechanisms underlying these effects remain poorly understood. The putative chromophore for these effects is cytochrome c oxidase, also known as complex IV (C-IV) of the mitochondrial electron transport chain (ETC). It is generally held that light absorption at C-IV initiates a cascade of events involving nitric oxide and reactive oxygen species (ROS) which subsequently results in increased ATP generation and improved cellular robustness. However, little is known about the mechanisms by which these pathways are initiated, and how they establish the observed beneficial outcomes. To probe these mechanisms, we have conducted low irradiance exposures of isolated mitochondria at a range of wavelengths and radiant exposures. We utilized a spectrophotometric method to make in vitro measurements of ETC complex enzyme activities, by observing changes in the redox state of the small electron carrier protein, cytochrome c. Specifically, we analyzed the enzyme kinetics of cytochrome c reductase, also known as complex III (C-III), and C-IV, with and without exposure to low irradiance light. Additionally, by utilizing C-III and C-IV inhibitors (Antimycin A and sodium cyanide, respectively) we are able to distinguish between effects acting directly on one complex or the other. In summary, this research represents a unique look at the earliest stages of PBM induction in the mitochondria, and its associated molecular mechanisms.