Multiple Cellular Photoacceptors (MCPs)

Multiple Cellular Photoacceptors refer to a diverse group of endogenous molecules, primarily located within the mitochondria and cell membranes, that possess the ability to absorb photons and convert light energy into biological signals. The most prominent member of this group is Cytochrome c oxidase (CCO), the terminal enzyme of the mitochondrial respiratory chain, which absorbs light in the red and near-infrared spectrum (Chung, H., et al., 2012). Other photoacceptors include non-visual opsins (such as OPN3 and OPN4), flavins, and porphyrins, which respond to shorter wavelengths like blue and green light. When these molecules absorb light, they undergo electronic excitation that can trigger the dissociation of inhibitory ligands like nitric oxide, thereby enhancing cellular respiration and ATP synthesis. This process, known as photobiomodulation, influences various downstream pathways involved in cell survival, inflammation reduction, and tissue repair (Hamblin, M. R., 2017). Consequently, these photoacceptors are the primary targets for light-based therapies used to treat conditions ranging from chronic pain and wound healing to neurodegenerative diseases. However, the term is considered a collective category rather than a single molecular target, as it encompasses various distinct proteins and enzymes with different absorption spectra and biological roles.

Other names

Cellular chromophoresMitochondrial photoacceptorsEndogenous photoacceptorsLight-sensitive moleculesBiological photoacceptors

The primary mechanism involves the absorption of photons by chromophores, most notably Cytochrome c oxidase (CCO) in the mitochondrial respiratory chain. This absorption leads to the photodissociation of inhibitory nitric oxide (NO) from the CCO catalytic center, which restores oxygen consumption and increases the mitochondrial membrane potential. This process results in enhanced ATP production and the release of low levels of reactive oxygen species (ROS), which act as secondary messengers to activate transcription factors (e.g., NF-kB, hypoxia-inducible factor) and downstream signaling pathways that promote cellular repair and anti-inflammatory responses (Karu, T. I., 1999; Hamblin, M. R., 2018).