What are the pigments of life?
The ‘pigments of life’ are molecules shaped as rings or horseshoes, called tetrapyrroles, that hold in their centre a metal ion. They colour our world and provide vital functions in all living beings. Examples are the green pigment chlorophyll, which captures light for photosynthesis in plants, the brown pigment haem, which transports oxygen for respiration in animals, and the magenta pigment vitamin B12, an essential nutrient in all domains of life.
In nature, cyclic tetrapyrroles are broken down by specialised enzymes that remove the caged metal, leaving behind the tetrapyrrole ‘skeletons’. These skeletons are usually also pigmented; for example, the haem skeletons of haemoglobin colour urine, faeces and eggshells. Moreover, thanks to the tetrapyrrole skeletons found in the fossil record, it is possible to infer about the environment where ancient algae and bacteria used to live.
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