Chlorophyll biosynthetic pathway

It has been demonstrated that peroxidizing herbicides interfere with the chlorophyll biosynthetic pathway (22) by accumulation of tetrapyrroles (17,18,23,24). It has also been shown that soluble plastidic cytochrome decreases when oxadiazon is present in a concentration when no peroxidation is yet apparent (25). For the identification of the tetrapyrrole the tolerant Bumilleriopsis was helpful. This species excretes large amounts of a tetrapyrrole into the liquid culture medium when treated with peroxidizing herbicides like oxadiazon, chlorophthalim, oxyfluorfen, or LS 82-556. The product found in the medium could be identified by mass and NMR spectrometry as protoporphyrin IX (17). 

EVIDENCE FOR A LIGHT-INDEPENDENT CHLOROPHYLL BIOSYNTHETIC PATHWAY IN ANGIOSPERM SEEDS GERMINATED IN DARKNESS. 

Evidence for a Light-Independent Chlorophyll Biosynthetic Pathway in Angiosperm Seeds Germinated in Darkness 687... 

Nonomnra, Y. et al.. Spectroscopic properties of chlorophylls and their derivatives inflnence of molecnlar stmctnre on the electronic state, Chem. Phys., 220, 155, 1997. Blairkenship, R.E., Identification of key step in the biosynthetic pathway of hacteri-ochlorophyU c and its implications for other known and nirknown green sulfur bacteria, J. Bacterial., 186, 5187, 2004. 

Figure 3.3 The tetrapyrrole biosynthetic pathways. Chelatases selectively insert Fe2+ to form haem, Mg2+ to form chlorophyll, Co2+ to form cobalamin and in methanogenic bacteria Ni2+ to form coenzyme F430.

Heme b is utilized for formation of hemoglobin, myoglobin, and many enzymes. It reacts with appropriate protein precursors to form the cytochromes c. Heme b is converted by prenylation to heme o405 and by prenylation and oxidation to heme fl.405a The porphyrin biosynthetic pathway also has a number of branches that lead to formation of corrins, chlorins, and chlorophylls as shown schematically in Fig. 24-22. 

Figure 24-22 Abbreviated biosynthetic pathways from 8-aminolevulinate to heme proteins, corrins, chlorophylls, and related substances.

Figure 24-23 Outline of the biosynthetic pathways for conversion of protoporphyrin IX into the chlorophylls and bacteriochlorophylls. After Bollivar et al.i17...

Branching of pathways is relevant in several cases. Thus, intermediates of the porphyrin biosynthetic pathway serve as precursors for chlorophyll (17, Fig. 2) and for the corrinoid ring systems of vitamin B12 (20, Fig. 2) (17). 1-Deoxy-D-xylulose 5-phosphate (43) serves as an intermediate for the biosynthesis of pyridoxal 5 -phosphate (39, Fig. 5), for the terpenoid precursor IPP (86) via the nonmevalonate pathway (Fig. 11), and for the thiazole moiety of thiamine pyrophosphate (46, Fig. 4). 7,8-Dihydroneopterin triphosphate (29, Fig. 3) serves as intermediate in the biosynthetic pathways of tetrahydrofolate (33) and tetrahydrobiopterin (31). The closely related compound 7,8-dihydroneopterin 2, 3 -cyclic phosphate is the precursor of the archaeal cofactor, tetrahydromethanopterin (34) (58). A common pyrimidine-type intermediate (23) serves as precursor for flavin and deazaflavin coenzymes. Various sulfur-containing coenzymes (thiamine (9), lipoic acid (7), biotin (6), Fig. 1) use a pyrosulfide protein precursor that is also used for the biosynthesis of inorganic sulfide as a precursor for iron/sulfur clusters (12). 

The MVA pathway was accepted as the unique biosynthetic pathway for the formation of aU isoprenoids in aU living organisms. Discrepancies with this general assertion appeared, however, as early as the 1950s (1, 2). For instance, -labeled MVA was not incorporated into chloroplast isoprenoids (e.g., carotenoids 25 and phytol 24 from chlorophylls Fig. 6), whereas it was well incorporated into phytosterols 27 synthesized in the cytoplasm. Unexpected labeling patterns were found in the prenyl chain of ubiquinone 22 in Escherichia coli at incorporation of C-labeled acetate. Finally, the labeling pattern in an isoprene unit from the sesquiterpenic pentalenene 21 series from a Streptomyces species at incorporation of uniformly... 

Terpenoids, which are also known as isoprenoids, constitute the most abundant and structurally diverse group of plant secondary metabolites, consisting of more than 40,000 different chemical structures. The isoprenoid biosynthetic pathway generates both primary and secondary metabolites that are of great importance to plant growth and survival. Among the primary metabolites produced by this pathway are phytohormones, such as gibberellic acid (GA), abscisic acid (ABA), and cytokinins the carotenoids, such as chlorophylls and plastoquinones involved in photosynthesis the ubiquinones required for respiration and the sterols that influence membrane stmcture (see also Steroid and Triterpene Biosynthesis) (Fig. 1). Monoterpenoids (CIO), sesquiterpenoids (Cl5), diterpenoids (C20), and... 

Aminolevulinic acid (ALA) is a common intermediate in the biosynthetic pathways of heme, chlorophylls, phycobilins, and cobalamins. Relationships between the various pathways are shown in Figure 21.27. 

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