Photopsin

Photopsin refers to a group of light-sensitive proteins found in the photoreceptor cells of the retina. These proteins are crucial for vision, as they are responsible for detecting light and initiating the visual signaling cascade. There are different types of photopsins, each sensitive to different wavelengths of light, which allows for color vision.

In humans, there are three main types of photopsins, also known as cone opsins, located in the cone cells of the retina. These are the S (short-wavelength), M (medium-wavelength), and L (long-wavelength) photopsins, corresponding to blue, green, and red light sensitivity, respectively. When a photon of light strikes a photopsin molecule, it causes a conformational change in a bound chromophore, retinal. This change triggers a G-protein signaling pathway that ultimately leads to an electrical signal being sent to the brain, where it is interpreted as vision. The different sensitivities of the three photopsins enable the brain to distinguish between various colors. Variations or deficiencies in these photopsins can lead to color vision deficiencies, such as red-green color blindness.