Pigments: chlorophyll and its synthesis

Published on October 1, 2007 Updated on February 9, 2021   42 min

A selection of talks on Biochemistry

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This talk deals with the metabolism of chlorophyll and related pigments presented by Wolfhart Rudiger from the Botanical Institute of the University of Munich.
The name chlorophyll is derived from the Greek words, chloros: green, and phyllon: leaf. It means the green of the leaf. The name chloroplast is, likewise, derived from this green pigment. The significance of chlorophyll for life on our globe is commonly known. The color of chlorophyll is sometimes even used as a synonym for life. In this sense, the poet, Johann Wolfgang von Goethe, apparently refers to chlorophyll with a famous sentence, "Grau teurer Freund ist alle Theorie und grun des Lebens goldner Baum." which translates to, "All theory, dear friend, is gray, but the precious Tree of Life is green." Chlorophylls are members of the large group of Metallo-tetrapyrroles; these have been named the pigments of life because they are widespread in nature and have important functions as prosthetic groups in many metabolic pathways, for example, in photosynthesis and respiration.
Chlorophyll biosynthesis is part of a network of branching pathways, leading to the formation of various Metallo-tetrapyrroles. Typically, such a network starts from simple compounds like amino acids. The first intermediates up to the first branching point are common for all pathways. Branching points are, uroporphyrinogen III, protoporphyrin IX, and sirochlorine. The end products include, amongst others, iron-containing heme, the prosthetic group of hemoglobin, of myoglobin, and of many cytochromes. Siroheme, the prosthetic group of nitrite reductase and sulfite reductase. Cobalt containing corrinoids of which vitamin B12 is best known, nickel-containing coenzyme F-430 of Metallo bacteria, and metal-free phycobilins. Of these pathways, only those related to chloroplasts will be discussed in this talk. Typical for photosynthetic organisms are in general, magnesium-containing chlorophylls and bacteria chlorophylls. An exception, however, is the genus acidiphilium which is a group of acidophilic bacteria that photosynthesize under aerobic conditions. This genus contains zinc bacteriochlorophyll in both the antenna intellection center. However, because only magnesium-containing bacteria chlorophyll precursors were detected, one must assume that zinc is introduced in exchange for magnesium only at a late biosynthetic step, ending with zinc bacteriochlorophyll and the secondary product of the magnesium branch. In plants and other plastid containing organisms, the complete pathway of the magnesium branch is confined to the plastid compartments. The steps that are common for all branches in organisms ranging from archaea to eubacteria, to eukarya, including animals and humans, these are not only formally identical but also catalyzed by homologous enzymes that are encoded by homologous genes. The first specific precursor molecule of tetrapyrroles formation