Biosynthesis of chlorophyll

Chlorophyll b occurs as an accessory pigment of the light-harvesting systems in land plants and green algae, and comprises one-third (or less) of total chlorophyll. The biosynthesis of chlorophyll b has been an area of active research particularly regarding its compartmentalization in chloroplast membranes, identification of the gene for chlorophyllide a oxidase, and characterization of the enzymes involved. ... 

Whereas the biosynthesis of chlorophylls a and b in higher plants has been described in detail, the synthesis and regulation of related substances found in less well-known algal groups and lower plants are largely unknown and will be areas of scientific interest in the future. Different and new types of chlorophylls and related substances have been reported and little is known about their possible biological... 

Rudiger, W., Biosynthesis of chlorophylls a and b the last steps, in Chlorophylls and Bacteriochlorophylls Biochemistry, Biophysics, Functions and Applications, 25, Grimm, B. et al., Eds., Springer, Dordrecht, 2006, chap. 14. 

Uracil derivatives can also function as herbicides by inhibition of the enzyme protoporphyrinogen-IX-oxidase (PRO), which is involved in the biosynthesis of chlorophyll <2006H(68)561>. Commercial examples of such PPO inhibitors include isocil 1104, bromacil 1105, terbacil 1106, flupropacil 1107, lenacil 1108, butafenacil 1109, and benzfendizone 1110 (Figure 9). 

From a photochemical reduction of the water-soluble porphyrin 32, hydrogen was obtained in a reaction sequence (Scheme 2) simulating the biosynthesis of chlorophyll as well as the hydrogen formation in photosynthesis (82AG132). 

Leeper FJ (1991) Intermediate steps in the biosynthesis of chlorophylls. In Scheer H (ed) Chlorophylls. CRC Press, Boca Raton, p 407... 

A number of other herbicides interfere with photosynthesis in specific ways. Amitrole inhibits biosynthesis of chlorophyll and carotenoids. The affected plants present a bleached appearance before they die because of the loss of their characteristic pigments. Another herbicide, atrazine, inhibits the oxidation of water to hydrogen ion and oxygen. Still other herbicides interfere with electron transfer in the two photosystems. In photosystem II, diuron inhibits electron transfer to plastoquinone, whereas bigyridylium herbicides accept electrons by competing with the electron acceptors in photosystem I. The inhibitors active in photosystem I include diquat and paraquat. The latter substance attained some notoriety when it was used to interfere with an... 

The biosynthesis of chlorophylls diverges from that of heme at the metal insertion stage. Magnesium is inserted into protoporphyrin IX by a little-known enzyme, called magnesium chelatase, followed by esterification of the propionic acid side chain on C-13 by transfer of a methyl group from... 

Interestingly, the biosynthesis of chlorophyll may be a window looking back into evolution. In this biosynthetic pathway, porph3uins are formed... 

C12H21N3O6, Mr 303.32, monohydrate, mp. >240°C, [a] 3 -60.5° (H2O), pK, 6.97,9.13,9.75 (0.1 m KCIO4, 25 °C). A component of tobacco leaves (Nicotiana ta-bacum), seeds of Fagus sylvatica and related species N. regulates the biosynthesis of chlorophyll and is possibly involved in iron transport in plants, like mugineic acid (C,2H2oN20g, Mr 320.30) which is excreted from oat and rice roots, N. binds iron ions, and transports them into the plant. 

Photorespiration—The C2 Carbon Oxidation Cycle G. H. Larimer and T. J. Andrews Biosynthesis of Chlorophyll P. Castelfranco and S. Beale... 

Protoporphyrin IX (26) is enzymatically generated in solution so that it is quite easy to isolate intermediates of the biosynthetic pathway (49). However the second part of chlorophyll biosynthesis takes place in the chloroplasts (49, 50). All enzymes participating in the formation of chlorophylls are located in the membrane and closely associated to each other so that the isolation of intermediates is very difficult. The identification of biosynthetic intermediates is also complicated by the fact that the structures become more and more lipophilic at the end of the biosynthetic chain making them insoluble in water. Another difficulty results from the lack of specificity of the enzymes involved in the late chlorophyll biosynthesis leading very often to an interchange of reaction steps in the biosynthetic sequence. Due to this very complicated situation it is intended here to give only a rough overview of the biosynthesis of chlorophyll a (2) 49-51). 

Protoporphyrin IX is a precursor for the biosynthesis of heme, chlorophyll, and cytochrome. Bile pigment is also derived from heme. The structure of bilirubin, the main component of this bile pigment, is shown [7]. Bilirubin is also a main component of the crude drug Go-Oh (bezoar, concave) prepared from the unhealthy calculus in the gallbladder or bile duct of cattle. Bezoar is an animal preparation used for detoxification, as an antipyretic, and as a cardiotonic. The biosynthesis of chlorophylls and bacte-riochlorophylls from protoporphyrin IX has been reviewed [8]. 

Also, as shown in Scheme 14.31, incorporation of magnesium with the aid of magnesium chelatase (EC 6.6.1.1.) leads to magnesium protoporphyrin IX, now committed to the biosynthesis of chlorophyll. 

We have described the biosynthesis (p. 238) of porphyrins from 8-aminolevulinic add via porphobilinogen. On to this basic process are superimposed a considerable number of variations. By insertion of iron into the protoporphyrin nucleus we obtain what Granick has called the iron branch of the biosynthetic chain (p. Ill), and a number of other variants have been described in these pages. Protoporphyrin is also the starting point for the biosynthesis of chlorophyll (the magnesium branch of Granick) as well as for the biosjmthesis of haem. 

Biosynthesis.—Further evidence has been adduced for the formation of 5-ALA and magnesium protoporphyrin-IX from glutamate in greening plants,and the enzymic preparation of the monomethyl ester of magnesium protoporphyrin has been described." Intermediates in the last stages of chlorophyll biosynthesis in which the geranylgeranyl side-chain is converted into phytyl have been studied l- C-labelled acetate is incorporated into the expected alternate positions in the phytyl ester side-chain (as shown by C n.m.r. spectral studies), but only low incorporations of mevalonate were obtained, presumably because of poor transport into the cell. The biosynthesis of chlorophyll-f has also been studied." ... 

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