Respiratory pigment Respiratory pigment A respiratory pigment is a molecule, such as hemoglobin in humans and other vertebrates, that increases the oxygen-carrying capacity of the blood. The four most common invertebrate respiratory pigments are hemoglobin, hemocyanin, hemerythrin and chlorocruorin. Hemoglobin is bright red when oxygenated, and dark red(purplish) when deoxygenated, oxygenated hemocyanin is blue in colour, deoxygenated it is almost colourless. Oxygenated chlorocruorin turns from green to red, whereas oxygenated hemerythrin is a violet to pink colour and colourless when deoxygenated. Any of various coloured conjugated proteins, such as hemoglobin, occur in living organisms and function in oxygen transfer in cellular respiration.
Photosynthetic pigment other groups of bacteria use the bacteriochlorophyll pigments (similar to the chlorophylls) for photosynthesis. Unlike the cyanobacteria, these bacteria do not produce oxygen; they typically use hydrogen sulfide rather than water as the electron donor. Recently, a very different pigment has been found in some marine γ-proteobacteria: proteorhodopsin. It is similar to and probably originated from bacteriorhodopsin (see below: under Archaea). Bacterial chlorophyll b has been isolated from Rhodopseudomonas spp. but its structure is not yet known to us. Halobacteria use the pigment bacteriorhodopsin which acts directly as a proton pump when exposed to light. Photosynthetic pigment A photosynthetic pigment