Biosynthesis and properties of cholorophyll

plant physiology

1. Biosynthesis and Properties of chlorophyll Picture representing the title of the Topic By Shariqa Aisha University of Kashmir Department of Bioresources

2. Learning objectives Introduction Discovery Chemical structure Properties of chlorophyll Biosynthesis of Phytol chain Biosynthesis of Chlorophyllide

3. Chlorophyll is a green photosynthetic pigment found in plants, algae, and cyanobacteria. Chlorophyll absorbs mostly in the blue and to a lesser extent red portions of the electromagnetic spectrum, hence its intense green color. Green substance in producers that traps light energy from the sun, which is then used to combine carbon dioxide and water into sugars in the process of photosynthesis Chlorophyll is vital for photosynthesis, which helps plants get energy from light. Chlorophyll molecules are specifically arranged in and around pigment protein complexes called photosystems, which are embedded in the thylakoid membranes of chloroplasts. Plants are perceived as green because chlorophyll absorbs mainly the blue and red wavelength and reflects the green. Introduction

4. Chlorophyll was first isolated and named by Joseph Bienaime Caventou and Pierre Joseph Pelletier in 1817 . After initial work done by German chemist Richard Willstatter spanning from 1905 to 1915, the general structure of chlorophyll a was elucidated by Hans Fischer in 1940. Joseph Bienaime Caventou Pierre Joseph Pelletier Richard Willstatter Discovery

5. Chlorophylls are numerous in types, but all are defined by the presence of a fifth ring beyond the four pyrrole-like rings . Most chlorophylls are classified as chlorins, which are reduced relatives of porphyrins (found in hemoglobin). They share a common biosynthetic pathway with porphyrins, including the precursor uroporphyrinogen III . Unlike hemes, which have iron at the center of the tetrapyrrole ring, chlorophylls have magnesium at the center. The chlorin ring can have various side chains, usually including a long phytol chain. Chemical structure

6. The most widely distributed form in terrestrial plants is chlorophyll a . The chlorophyll molecule is made up of two moieties of distinct origin—chlorophyllide and phytol . The phytyl side-chain derives from the plastidic isoprenoid biosynthetic pathway. The initial steps in chlorophyllide synthesis , from the biosynthesis of δ -aminolevulinate to protoporphyrinogen IX, occur in the soluble phase of plastids, whereas the subsequent steps are membrane-bound . The initial steps leading to the synthesis of uroporphyrinogen III are common to all tetrapyrroles that are synthesized in chloroplasts (chlorophyll, heme, phytochromobilin, siroheme).

7. Chlorophyll is found in virtually all photosynthetic organisms including green plants, cyanobacteria and algae. It absorbs energy from light and this energy is then used to convert carbon dioxide to carbohydrates. C hlorophyll have a tadpole like structure. There is porphyrin head and a phytol tail. P orphyrin head consists of four pyrrole rings with a central magnesium atom connected with four nitrogen atoms. T he long hydrophobic phytol tail is lipid soluble and it is anchored in the thylakoid membrane. Physical & chemical p roperties of chlorophyll

8. The head is hydrophilic and generally lies in the surface of the membrane . The intense green color of chlorophyll is due to its strong absorbencies in red and blue regions of the spectrum. Because of these absorbencies the light it reflects and transmits appears green. Due to the green color of chlorophyll , it has many uses as dyes and pigments. It is used in coloring soaps, waxes, oils and confectioneries. Chlorophyll a and chlorophyll b :soluble in a alcohol, ether, benzene, acetone , and insoluble in water . The melting point of chlorophyll a is 152°C and the of chlorophyll b is 125°C.

9. It has antibacterial properties. It removes harmful toxins from the body. It speeds up would healing. It stimulates bowel function. It helps in reducing weight. It strengthens the immune system. It lowers blood pressure. It protects against carcinogens. It lowers cholesterol. It purifies blood. Beneficial properties

10. The 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway provides isopentenylpyrophosphate (IPP) for synthesis of the central intermediate geranylgeranyl diphosphate (GGDP) for plastidial isoprenoids. This process involves the following steps: The first step of the MEP pathway combines glyceraldehyde3-phosphate and pyruvate—a reaction catalyzed by 1-deoxyD-xylulose 5-phosphate synthase to form deoxy-D-xylulose 5-phosphate . The second step involves a reductive isomerization by a 1-deoxy-D-xylulose 5-phosphate reductoisomerase on deoxy- D-xylulose 5-phosphate and yields MEP (2C-methyl-D-erythritol 4-phosphate). Biosynthesis of phytol - chain from isoprenoid pathway

11. iii) The introduction of a cytidyl moiety by 2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase to produce 4-diphosphocytidyl-2C-methyl-D-erythritol. 4-diphosphocytidyl-2C-methyl-D-erythritol is phosphorylated by 4-(cytidine 5’diphospho) 2-C-methyl-D-erythritol kinase and then cyclized after loss of the cytidyl group to yield 2-C-methyl-D-erythritol 2,4cyclodiphosphate _reaction catalyzed by 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase. The active C5 unit (IPP) and DMAPP are then formed in final steps catalyzed by two enzymes: 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate synthase and reductase .

12. IPP( isoprenoid pyrophosphate) once synthesized undergoes a sequential series of condensation reactions to form geranylgeranyl diphosphate ( GGDP). GGDP is a central intermediate in the synthesis of plastidic isoprenoids: chlorophylls (phytyl side-chain), carotenoids and prenylquinones (isoprenoid side-chains. Geranylgeranyl Diphosphate Synthesis :

13. Glyceraldehyde 3-phosphate + pyruvate 1-deoxy-D-xylulose 5-phosphate 2C-methyl-D-erythritol 4-phosphate 4-diphosphocytidyl-2C-methyl-D-erythritol 4-diphosphocytidyl-2C-methyl-D-erythritol-2-phosphate 2C-methyl-D-erythritol 2,4-cyclo-diphosphate 1-hydroxy-2-methyl-2-butneyl 4-diphosphate isopentenyl pyrophosphate dimethylally diphosphate GGPP CHLOROPHYLL (phytol)

14. Synthesis of Protoporphyrin IX : The first step involves the conversion of L-glutamate to glutamate 1-semialdehyde which is catalysed by the enzyme Glutamyl-tRNA synthetase . Glutamate 1-semialdehyde gets converted into 5 aminolevulinic acid by the enzyme Glutamate 1-semialdehyde aminotransferase 1. Enzyme aminolevulinate dehydratase then converts 5 aminolevulinic acid into Porphobilinogen. Porphobilinogen gets converted into Hydroxymethylbilane by the enzyme Porphobilinogen deaminase. Biosynthesis of Cholorophyllide

15. Hydroxymethylbilane in the presence of enzyme Uroporphobilinogen III synthase forms Uroporphobilinogen III. Uroporphobilinogen III then in the presence of enzyme coproporphyrinogen III decarboxylase and oxidase forms Coproporphyrinogen III. Corproporphyrinogen III in the presence of enzyme protoporphyrinogen oxidase forms Protoporphyrin IX. The first enzymes of the pathway (i.e. up to protoporphyrinogen IX oxidase) are located in the stroma.

16. The second phase of chlorophyll biosynthesis is associated with chloroplast membranes in a complex manner. This involves the formation of Mg-protoporphyrin IX, catalyzed by the enzyme Mg -chelatase . Mg-chelatase catalyses the reaction by inserting Mg 2+ protoporphyrin IX. Mg-Protoporphyrin IX Synthesis

17. This involves the formation of Mg-protoporphyrin IX Monomethyl Ester from Mg-protoporphyrin IX and the reaction is catalysed by Mg-protoporphyrin IX methyltransferase. Mg-protoporphyrin IX Monomethyl Ester then gets converted into Protochlorophyllide in the presence of enzyme Mg-protoporphyrin IX Mecyclase. protochlorophyllide in the presence of enzyme protochlorophyllide oxidoreductase forms Chlorophyllide a. Protochlorophyllide and Chlorophyllide Synthesis

18. The chlorophyll synthase performs the esterification of chlorophyllide (a and b ), the last step of chlorophyll biosynthesis. The cholorophyllide a on addition with phtyl-PP in the presence of enzyme chlorophyll synthase yeilds chlorophyll a. Chlorophyll b is then formed from chlorophyll a by the enzyme chlorophyll a oxygenase.

19. Cholorophyllide Biosynthesis

20. References