Establishing Plant’s Blood Relatives

Two of the most fundamental processes in life, the transport of oxygen by blood in animals and the absorption of light during photosynthesis in plants, rely on pigments to carry out their highly important missions. Hans Fischer received the 1930 Nobel Prize in Chemistry for showing how Nature constructs these different coloured pigments from the same chemical building blocks.

Chemists knew that haemoglobin, the complex oxygen-transporting molecule in blood, can be divided into one portion that contains the red pigment and another so-called protein part. Through isolating and examining crystals of the pigment-containing part, known as haemin or haem, Fischer could identify its chemical components. Fischer discovered that haemin could be broken down into less complex compounds called porphyrins, and that in turn these could be broken down into relatively simpler compounds that share ring-like structures with a group of chemicals called pyrroles. Reversing this process, he successfully achieved the considerable feat of artificially synthesising haemin completely from its simplest chemical constituents.

Structural similarities between haemoglobin and the plant pigment chlorophyll had been uncovered by the 1915 Chemistry Laureate Richard Willstätter, when he showed that chlorophyll holds an atom of magnesium within the centre of the molecule in the same way in which iron is held within haemin. Fischer provided a more detailed view of this similarity when he showed that chlorophyll is constructed from the same pyrrole constituents that make up haemin. He subsequently found that other biologically important pigments are derived from the same blood line of chemicals. Chief amongst these is bilirubin, a bile pigment that is derived from haemin, and which is responsible for the yellowing skin colour of patients suffering from jaundice.

First published 2 April 2009

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