Chlorophyll Magnesium Research Articles

Illuminating the black box of B 12 biosynthesis

Tetrapyrroles are nearly ubiquitous in nature as participants in a wide variety of biological reactions that are central to life, such as electron transfer, gas binding, and one-carbon metabolism (1, 2). Because of their diverse colors—for example the greens of plant chlorophylls, reds of blood, and blues and browns of avian eggs—tetrapyrroles have been called the “pigments of life.” The chemical diversity of cyclic tetrapyrroles owes much to their ability to coordinate a variety of redox active metals in a fashion that allows for fine-tuning of midpoint potentials, increasing or decreasing reactivity of the metal center, and providing protection against undesirable side reactions. One finds magnesium in chlorophyll, iron in hemes, nickel in factor F430, and cobalt in cyano-cobalamin (vitamin B12) (Fig. 1). Although hemes and chlorophyls are synthesized by both prokaryotes and eukaryotes, factor F430, which is involved in methanogenesis, is produced only by some archae, and cobalamin synthesis is found only in bacteria and archae. With regard to cobalamin, it has long been known that two distinct pathways exist for its biosynthesis, one aerobic and the other anaerobic. Whereas the genes required for both aerobic and anaerobic synthesis have been known, the actual mechanism for synthesis via the anaerobic pathway has remained a large “black box” in what is one of the longest known biosynthetic pathways. However, the contents of this box have now been identified and characterized, thanks to an elegant study that can properly be called a tour de force by Moore et al. at the University of Kent (3). Fig. 1. The family of tetrapyrroles originating from uroporphyrinogen III. The central metal atom is colored to represent the color of the metallo-tetrapyrrole. … [↵][1]1E-mail: hdailey{at}uga.edu. [1]: #xref-corresp-1-1

Preferential pathways for light-trapping involving β-ligated chlorophylls

The magnesium atom of chlorophylls (Chls) is always five- or six-coordinated within chlorophyll–protein complexes which are the main light-harvesting systems of plants, algae and most photosynthetic bacteria. Due to the presence of stereocenters and the axial ligation of magnesium the two faces of Chls are diastereotopic. It has been previously recognized that the α-configuration having the magnesium ligand on the opposite face of the 17-propionic acid moiety is more frequently encountered and is more stable than the more seldom β-configuration that has the magnesium ligand on the same face [T.S. Balaban, P. Fromme, A.R. Holzwarth, N. Krauβ, V.I. Prokhorenko, Relevance of the diastereotopic ligation of magnesium atoms in chlorophylls in Photosystem I, Biochim. Biophys. Acta (Bioenergetics), 1556 (2002) 197–207; T. Oba, H. Tamiaki, Which side of the π-macrocycle plane of (bacterio)chlorophylls is favored for binding of the fifth ligand? Photosynth. Res. 74 (2002) 1–10]. In photosystem I only 14 Chls out of a total of 96 are in a β-configuration and these occupy preferential positions around the reaction center. We have now analyzed the α/β dichotomy in the homodimeric photosystem II based on the 2.9 Å resolution crystal structure [A. Guskov, J. Kern, A. Gabdulkhakov, M. Broser, A. Zouni, W. Saenger, Cyanobacterial photosystem II at 2.9 Å resolution: role of quinones, lipids, channels and chloride, Nature Struct. Mol. Biol. 16 (2009) 334–342] and find that out of 35 Chls in each monomer only 9 are definitively in the β-configuration, while 4 are uncertain. Ab initio calculations using the approximate coupled-cluster singles-and-doubles model CC2 [O. Christiansen, H. Koch, P. Jørgensen, The second-order approximate coupled cluster singles and doubles model CC2, Chem. Phys. Lett. 243 (1995) 409–418] now correctly predict the absorption spectra of Chls a and b and conclusively show for histidine, which is the most frequent axial ligand of magnesium in chlorophyll–protein complexes, that only slight differences (< 4 nm) are encountered between the α- and β-configurations. Significant red shifts (up to 50 nm) can, however, be encountered in excitonically coupled β–β-Chl dimers. Surprisingly, in both photosystems I and II very similar “special” β–β dimers are encountered at practically the same distances from P700 and P680, respectively. In purple bacteria LH2, the B850 ring is composed exclusively of such tightly coupled β-bacteriochlorophylls a. A statistical analysis of the close contacts with the protein matrix (< 5 Å) shows significant differences between the α- and β-configurations and the subunit providing the axial magnesium ligand. The present study allows us to conclude that the excitation energy transfer in light-harvesting systems, from a peripheral antenna towards the reaction center, may follow preferential pathways due to structural reasons involving β-ligated Chls.

Bioinorganic chemistry: a short course

Chapter 1: Inorganic Chemistry Essentials. Introduction . Essential Chemical Elements. Metals in Biological Systems: A Survey. Inorganic Chemistry Basics. Biological Metal Ion Complexation. Thermodynamics. Kinetics. Electronic and Geometric Structures of Metals in Biological Systems. Bioorganometallic Chemistry. Electron Transfer. Introduction to Biological Metal Homeostasis, Transport, and Storage. Chapter 2: Biochemistry Fundamentals. Introduction. Proteins. Amino Acid Building Blocks. Protein Structure. Protein Sequencing and Proteomics. Protein Function, Enzymes and Enzyme Kinetics. Nucleic Acids. DNA and RNA Building Blocks. DNA and RNA Molecular Structures. Transmission of Genetic Information. Genetic Mutations and Site-Directed Mutagenesis. Genes and Cloning. Genomics and the Human Genome. The ATP-binding cassette (ABC) Transporter Superfamily. Chapter 3: Instrumental Methods. Introduction. Analytical Instrument-Based Methods. Spectroscopy. X-ray Absorption Spectroscopy (XAS) and Extended X-ray Absorption Fine Structure (EXAFS). Theoretical Aspects and Hardware. Descriptive Examples. X-ray Crystallography. Introduction. Crystallization and Crystal Habits. Theory and Hardware. Descriptive Examples. Electron Paramagnetic Resonance. Theory and Determination of g-values. Hyperfine and Superhyperfine Interactions. Descriptive Examples. Nuclear Magnetic Resonance. Theoretical Aspects. Nuclear Screening and the Chemical Shift. Spin-Spin coupling. Techniques of Spectral Integration and Spin-Spin Decoupling. Nuclear Magnetic Relaxation. The nuclear Overhauser Effect (NOE). Obtaining the NMR spectrum. Two-dimensional NMR Spectroscopy. Correlation Spectroscopy (COSY). Nuclear Overhauser Effect Spectroscopy (NOESY). Descriptive Examples. Mossbauer Spectroscopy. Theoretical Aspects. Quadrupole Splitting and the Isomer Shift. Magnetic Hyperfine Interactions. Descriptive Examples. Atomic Force Microscopy. Fast Methods. Stopped-Flow Kinetic Methods. Flash Photolysis. Time-Resolved Crystallography. Chapter 4: Introduction to Computer-Based Methods. Computer Hardware . Molecular Modeling and Molecular Mechanics. Introduction to MM. Molecular Modeling, Molecular Mechanics and Molecular Dynamics. Biomolecule Modeling. Molecular Modeling Descriptive Examples. Quantum Mechanics-Based Computational Methods. Introduction. Ab-initio Methods. Density Functional Theory. Semi-empirical Methods. Computer Software for Chemistry. Mathematical Software. World Wide Web Online Resources. Nomenclature and Visualization Resources. Online Societies, Literature, Materials, Equipment Webservers. Chapter 5: Group I and II metals in biological systems. Transport and storage of metal ions. Homeostasis involving Na+, K+, Ca2+, Mg2+, Zn2+ (as well as P, Cl, and H). Movement of molecules and ions across membranes. Proton pumps. Ion pumps. Active versus passive transport . Na+/ K+ ATPases. Magnesium dependent biomolecules. Kinases. ATP-pumps. Catalytic RNA and Magnesium. Magnesium in chlorophyll. Calcium dependent biomolecules. Calmodulins and triggering. Biochemistry of nitrogen oxides, nitroxyl, and peroxynitrite ion. Chapter 6: Iron Containing Proteins and Enzymes. Iron-containing proteins with porphyrin ligand systems. Hemoglobin and Myoglobin (first edition material somewhat condensed). Cytochrome P-450: a monooxygenase. Iron-containing cytochromes in photosynthesis. Green plant cytochromes. Cytochrome bc559. Cytochrome bf. Bacterial cytochromes. Cytochrome c2. Cytochrome bc1. Iron-containing cytochromes in the respiratory pathway. Cytochrome c. Cytochrome c oxidase. Non-Heme Iron-containing proteins. MMO-Methane Monooxygenase. Catechol dioxygenases. Iron-oxo clusters. Transferrin for metal transport . Ferritin for metal storage. Hemerythrin. Purple acid phosphatase. Iron-sulfur cluster proteins. Rubredoxin. Ferrodoxins. Aconitase. Chapter 7: Enzymes containing zinc, nickel, and enzymes with multiple metal cofactors. Zinc homeostasis, transport, and storage. Zinc Enzymes. Alkaline phosphatase. Alcohol dehydrogenase. Aspartate transcarbamoylase. Carbonic anhydrase. Carboxypeptidase A and B. Zinc Fingers. Nickel Enzymes. Urease. F430. Enzymes with multiple metal cofactors. Hydrogenases. Carbon monoxide dehydrogenases. Chapter 8 Disease, Disease Diagnosis and Treatment Utilizing Inorganic Species. Metal Transport and Metallochaperones. Disease States. Metal deficiency. Metal toxicity. Copper toxicity. FALS. Wilson and Menkes diseases. Disease Diagnosis. Technetium Imaging Agents. Gadolinium MRI Imaging Agents. Quantum Dots for In vivo Imaging. Metals in Medicine. Manganese superoxide mimetics. Vanadium-based Diabetes Drugs. Platinum-containing Anticancer Agents. Nanomedicine.

Off-line separation and determination of rare earth elements associated with chloroplast pigments of hyperaccumulator Dicranopteris dichotoma by normal-phase liquid chromatography and ICP-MS.

An off-line normal-phase liquid chromatography-ICP-MS method has been used for separation and determination of the rare earth elements (REE) associated with chloroplast pigments of Dicranopteris dichotoma. The stability of REE-bound pigments was tested, and almost no destruction of REE-bound pigments occurred during the so-called normal-phase liquid chromatography. The accumulated free REE ions on the microcrystalline cellulose column were cleaned by elution with 5 mmol L(-1) 2-ethylhexyl hydrogen 2-ethylhexylphosphonate (P507), to avoid exchange of these free ions with metals from the pigments. When these precautions were taken, the method was applied to the study of REE-bound pigments in D. dichotoma. ICP-MS results showed REE were present in chlorophylls and lutein, although REE concentrations in carotene and pheophytin were both below procedural blank levels. By careful analysis of the eluate fractions containing chlorophyll a it was found that REE-bound chlorophyll a in D. dichotoma was slightly enriched in the fractions with relatively short retention time. Results indicated that the retention time of REE-bound chlorophyll a might be slightly less than that of magnesium chlorophyll a, and REE-bound chlorophylls might be of relatively low polarity in comparison with magnesium bound chlorophylls. This phenomenon could be explained by the special double-decker sandwich-structure of REE-bound chlorophylls, as was reported by us and other authors. On the basis of these results we preferred to consider that REE can replace magnesium in chlorophyll a of D. dichotoma, and that the role of REE-bound chlorophylls in photosynthesis cannot be neglected. These data might be useful for understanding of both the properties of REE-bound pigments and the effect of REE on plant photosynthesis.

Discriminative Determination of Copper, Iron and Magnesium in Chlorophyll and Chlorophyllin Complexes and Their Contents in Foods

A convenient discriminative determination of copper (Cu), iron (Fe), magnesium (Mg) in chlorophyll and chlorophyllin complexes was developed. Vegetable samples were extracted with ethanol, and chewing gum samples with n-butyl acetate, ethanol and water. The metal chlorophyll (Cu, Fe and Mg) and metal chlorophyllin (Cu, Fe and Mg) in the extracts were purified and separated at either pH 8-9 or pH 5-6 by making use of partition chromatography with n-butyl acetate-ethanol-water (10:40:60). The metal in the discriminated chlorophyll and chlorophyllin was determined with a flame-type atomic absorption spectrometer.The recoveries of metal chlorophylls and chlorophyllins were as follows: Cu chlorophyll, 88%; Fe chlorophyll, 64%; Mg chlorophyll, 79% and Cu chlorophyllin, 87%; Fe chlorophyllin, 80%; Mg chlorophyllin, 87%.We have carried out a survey on metal chlorophyll and chlorophyllin in 36 vegetables and 5 chewing gums and found that some of them contained metal chlorophylls and chlorophyllins at the level of 0.1ppm or over.

Speciation studies of copper and magnesium in duckweed extract using interfaced HPLC and thermospray nebulizer flame AA

Abstract Studies on duckweed extract indicated that at least some of the magnesium in chlorophyll was replaced by copper. The copper combined not only with chlorophyll, but also with some other plant pigments in duckweed. The study also demonstrated that HPLC‐AA can be used to study the speciation of the copper and magnesium in duckweed, revealing the total number of such compounds present and the associated organic compounds. HPLC‐AA has the potential of extensive speciation application in many fields of science. To obtain the information needed the electronic spectra and HPLC‐AA chromatograms of three samples of treated duckweed were recorded. The three samples were: (i) A sample of solution extracted with ethanol from duckweed (DW‐extract); (ii) the product of reaction between DW‐extract and copper aqueous solution; (iii) the extract of duckweed which has been pretreated with copper aqueous solution at pH 5.0.

Studies on the Infection and the Multiplication of Plant viruses

The present paper dealts with the results of studies on the breakdown of chlorophyll in tobacco leaves systemically infected with CMV. The major findings are as follows: chlorophyllase activity gradually decreases and chlorophyll contents rapidly decreases as viral infection progresses. High content of pheophytin, a form lacking magnesium in chlorophyll, is found in the mosaic and yellowish areas of infected leaves but the amounts of chlorophyllides and pheophorbides are negligible in the same areas. Pheophytin is never produced from chlorophyll by the optimal reaction of chlorophyllase or proteolytic enzyme. These results suggest that the breakdown of chlorophyll in the leaves showing mosaic is mainly due to the conversion of chlorophyll to pheophytin by the alteration of intracellular environment that occurs as a result of viral infection.The concentration of carotenoids increases also in the mosaic and yellowish areas of infected leaves. Especially, xanthophyll. a yellow pigment, increases markedly.The content of fraction I protein in infected leaves dereases remarkably as the symptoms progress. The decrease of fraction I protein content is found to be closely correlated with the breakdown of chlorophyll. But, the mechanisms by which these two materials are degraded appear to be different.

Production of Hyperglycemia in Rabbits by Subcutaneous Injections of Magnesium Salts.

The presence of magnesium in chlorophyll, and the important role of the latter in the metabolism of carbohydrates in plants, led us to study the effect of magnesium salts on blood sugar in rabbits. Five normal rabbits, starved for 24 hours, were injected subcutaneously with a 5 per cent solution of MgCl2 or MgSO4, using 5 cc. of this solution per kilo of body weight. During the experiment the rabbits were kept quiet in a tray, without restraint, and there was no struggle when the 2 cc. of blood were taken from the marginal ear vein. Such moderate bleeding does not affect essentially the blood sugar level in rabbits, as shown in a previous paper1.The results of the experiments are presented in the following table:This table shows that subcutaneous injection of magnesium salts produces a marked hyperglycemia, with a maximum in from 2 to 2 1/2 hours. In 5 1/2 hours the blood sugar is not far from its initial level, and in 24 hours it has reached a normal value. Controls, on the hemoglobin content, show that ...