scholarly journals Biosynthesis of the modified tetrapyrroles—the pigments of life

2020 ◽  
Vol 295 (20) ◽  
pp. 6888-6925 ◽  
Author(s):  
Donald A. Bryant ◽  
C. Neil Hunter ◽  
Martin J. Warren
Keyword(s):  
Chemical Reactions ◽  
Metal Ion ◽  
Side Chain ◽  
Vitamin B ◽  
Metal Chelation ◽  
Macrocyclic Compounds ◽  
Comparative Biochemistry ◽  
Chain Composition ◽  
Almost All ◽  
Life On Earth

Modified tetrapyrroles are large macrocyclic compounds, consisting of diverse conjugation and metal chelation systems and imparting an array of colors to the biological structures that contain them. Tetrapyrroles represent some of the most complex small molecules synthesized by cells and are involved in many essential processes that are fundamental to life on Earth, including photosynthesis, respiration, and catalysis. These molecules are all derived from a common template through a series of enzyme-mediated transformations that alter the oxidation state of the macrocycle and also modify its size, its side-chain composition, and the nature of the centrally chelated metal ion. The different modified tetrapyrroles include chlorophylls, hemes, siroheme, corrins (including vitamin B12), coenzyme F430, heme d1, and bilins. After nearly a century of study, almost all of the more than 90 different enzymes that synthesize this family of compounds are now known, and expression of reconstructed operons in heterologous hosts has confirmed that most pathways are complete. Aside from the highly diverse nature of the chemical reactions catalyzed, an interesting aspect of comparative biochemistry is to see how different enzymes and even entire pathways have evolved to perform alternative chemical reactions to produce the same end products in the presence and absence of oxygen. Although there is still much to learn, our current understanding of tetrapyrrole biogenesis represents a remarkable biochemical milestone that is summarized in this review.

Lignin peroxidase initiates O2-dependent self-propagating chemical reactions which accelerate the consumption of 1-(3′,4′-dimethoxyphenyl)propene

2000 ◽  
Vol 347 (2) ◽  
pp. 585-591 ◽  
Author(s):  
Rimko TEN HAVE ◽  
Maurice C. R. FRANSSEN ◽  
Jim A. FIELD
Keyword(s):  
Chemical Reactions ◽  
Lignin Peroxidase ◽  
Metal Ion ◽  
Consumption Rate ◽  
Peroxyl Radicals ◽  
Side Chain ◽  
Coupling Reactions ◽  
Air Atmosphere ◽  
Aromatic Substrates ◽  
Consumption Rates

Lignin peroxidase (LiP) has been used to study the Cα-Cβ cleavage of the propylene side chain in 1-(3ʹ,4ʹ-dimethoxyphenyl)propene (DMPP) to 3,4-dimethoxybenzaldehyde (veratraldehyde, VAD). Under an air atmosphere, LiP oxidized DMPP to VAD (27.8%) and 1-(3ʹ,4ʹ-dimethoxyphenyl)propan-2-one (DMPA, 8.7%), after 10 min of incubation. Dissolved O2 was rapidly consumed during DMPP conversion, of which one-third was converted into superoxide. The remaining two-thirds of the consumed O2 was involved in Cα-Cβ cleavage of DMPP to VAD and in self-propagating chemical reactions stimulating the consumption of DMPP. The involvement of peroxyl radicals, in the chemical consumption of DMPP, was confirmed by using the well-known peroxyl radical reductant Mn2+. This metal ion severely inhibited the DMPP consumption rate under air, but did not affect the lower enzymic DMPP consumption rate under N2. The substoichiometric requirement of LiP for H2O2 during DMPP oxidation could be explained in part by dismutation of superoxide, but more importantly by direct chemical reactions of DMPP-derived peroxyl radicals with fresh DMPP. Another VAD-producing route was found by incubating the DMPP oxidation product, DMPA, with LiP. Under air the molar yield of VAD was 29.7%. In the absence of O2, the Cα-Cβ cleavage of DMPA to VAD was strongly inhibited and side-chain coupling products (dimers) were formed instead. As a whole, the results suggest two new roles of O2 in LiP-mediated oxidation of aromatic substrates. First, O2 is responsible for the formation of reactive peroxyl intermediates, which can directly react with other substrate molecules and thereby accelerate consumption rates. Secondly, O2 can prevent coupling reactions by lowering the pool of carbon-centred radicals accumulating during LiP catalysis.

scholarly journals Physical principles of membrane organization

1980 ◽  
Vol 13 (2) ◽  
pp. 121-200 ◽  
Author(s):  
J. N. Israelachvili ◽  
S. Marčelja ◽  
R. G. Horn
Keyword(s):  
Chemical Reactions ◽  
Nerve Conduction ◽  
Energy Transduction ◽  
Molecular Organization ◽  
Cellular Structures ◽  
Cellular Activity ◽  
Simple Chemical ◽  
Unicellular Organisms ◽  
Almost All ◽  
Physical Principles

Membranes are the most common cellular structures in both plants and animals. They are now recognized as being involved in almost all aspects of cellular activity ranging from motility and food entrapment in simple unicellular organisms, to energy transduction, immunorecognition, nerve conduction and biosynthesis in plants and higher organisms. This functional diversity is reflected in the wide variety of lipids and particularly of proteins that compose different membranes. An understanding of the physical principles that govern the molecular organization of membranes is essential for an understanding of their physiological roles since structure and function are much more interdependent in membranes than in, say, simple chemical reactions in solution. We must recognize, however, that the word ‘understanding’ means different things in different disciplines, and nowhere is this more apparent than in this multidisciplinary area where biology, chemistry and physics meet.

Biocompatible fluorinated polyglycerols for droplet microfluidics as an alternative to PEG-based copolymer surfactants

Lab on a Chip ◽  
2016 ◽  
Vol 16 (1) ◽  
pp. 65-69 ◽  
Author(s):  
Olaf Wagner ◽  
Julian Thiele ◽  
Marie Weinhart ◽  
Linas Mazutis ◽  
David A. Weitz ◽  
...  
Keyword(s):  
Gene Expression ◽  
Cell Encapsulation ◽  
Droplet Microfluidics ◽  
Side Chain ◽  
Expression Studies ◽  
Chain Composition ◽  
Gene Expression Studies

Polyglycerol-based triblock surfactants with tailored side-chain composition are exemplified in cell encapsulation and in vitro gene expression studies in droplet-based microfluidics as alternative to PEG-based surfactants.

The Marine Environment

2020 ◽  
Author(s):  
Professor John Swarbrooke
Keyword(s):  
Marine Environment ◽  
Cold Water ◽  
Vital Role ◽  
Ocean Currents ◽  
The Sun ◽  
Weather Patterns ◽  
The World ◽  
Sheer Size ◽  
Almost All ◽  
Life On Earth

The fact that open ocean covers two-thirds of the surface of our planet dramati- cally illustrates the importance of the marine environment to life on Earth. But the importance of the oceans goes far beyond their sheer size for it is the oceans that largely determine our climate for the weather around the world is heavily influenced by what happens in our seas. ‘Weather patterns are primarily controlled by ocean currents which are influenced by surface winds, temperature, salinity, the Earth’s rotation and ocean tides....Ocean currents bring warm water and rain from the equator to the poles and cold water from the poles towards the equator’ (www.greentumble.com, 2016). Every schoolchild knows that the sun evaporates water from the sea which then become clouds that then produces almost all of the rain and snow which falls on every land mass in the world. The oceans also absorb heat from the sun and from human activities; this heat is then carried to the land in those places where the prevailing winds blow from the sea to the land. At the same time, the oceans play a vital role in the carbon cycle by absorbing carbon dioxide that is in the air.

Sources of Air Pollution

2018 ◽  
pp. 220-258
Author(s):  
Abderrezak Khelfi
Keyword(s):  
Air Pollution ◽  
Particulate Matter ◽  
Adverse Effects ◽  
Chemical Reactions ◽  
Dust Storms ◽  
Pollution Sources ◽  
Atmospheric Gases ◽  
Secondary Pollutants ◽  
Harmful Substances ◽  
Life On Earth

This chapter describes how air is a complex natural gaseous system essential to support life on Earth. Air pollution comes from a wide variety of sources, which discharge of harmful substances into the atmosphere, causing adverse effects to humans and the environment. They can be natural or anthropogenic. Natural air pollution sources are multiple and include volcanic eruption, fire, ocean vapors, dust storms and fermentation of organic materials. However, the range and quantities of chemicals discharged into the atmosphere from industry, transport, agriculture, energy production, domestic heating, and many other human activities, have increased dramatically. Some pollutants are emitted directly into the atmosphere and are known as primary pollutants (NOx, SOx, particulate matter, etc.). Others are formed in the air as a result of chemical reactions with other pollutants and atmospheric gases; these are known as secondary pollutants like ozone. This chapter provides an overview on air pollution sources as well as the ways in which pollutants can affect human health and the environment.

The aqueous chemistry of uranium minerals. Part I. Divalent cation zippeïte

1979 ◽  
Vol 43 (328) ◽  
pp. 539-541 ◽  
Author(s):  
David F. Haacke ◽  
Peter A. Williams
Keyword(s):  
Metal Ion ◽  
Metal Speciation ◽  
Divalent Metal ◽  
Free Energies ◽  
Naturally Occurring ◽  
Solution Studies ◽  
Chemical Studies ◽  
Divalent Metal Ion ◽  
Almost All ◽  
End Members

SynopsisFree energies of formation of divalent metal ion zippeïtes, M2(UO2)6(SO4)3(OH)10 ·nH2O, M = Mg,Co,Ni,Zn have been determined from solution studies and metal speciation calculations, in water. It is found that in the compounds, the number of molecules of water of crystallization is equal to 8. This is at variance with a previous report (Frondel et al., 1976), but it has been found that some at least of the water content of zippeite is either nonessential or very loosely bound in the structure. Based on the octahydrate formulation, values are −3506, −12695, −12683 and −12870±4 kJ mol−1 for the Mg,Co,Ni and Zn end-members, respectively. Almost all of the differences in the values are accounted for by those values for the metal ions alone with the exception of Znzippeïte where a discrepancy of some 22 kJ mol−1 is found. Even this value is small however, and the chemical studies indicate that extensive mutual solid solution between all end members is to be expected. These findings agree perfectly with observations on the composition of naturally occurring zippeite minerals of this group.

scholarly journals Gait after Birmingham Hip Resurfacing

2019 ◽  
Vol 101-B (11) ◽  
pp. 1423-1430 ◽  
Author(s):  
Anatole V. Wiik ◽  
Rhiannon Lambkin ◽  
Justin P. Cobb
Keyword(s):  
Metal Ion ◽  
Gait Pattern ◽  
Hip Resurfacing ◽  
Functional Change ◽  
Control Group ◽  
Healthy Controls ◽  
High Speeds ◽  
The Mean ◽  
Almost All ◽  
Gait Study

AimsThe aim of this study was to assess the functional gain achieved following hip resurfacing arthroplasty (HRA).Patients and MethodsA total of 28 patients (23 male, five female; mean age, 56 years (25 to 73)) awaiting Birmingham HRA volunteered for this prospective gait study, with an age-matched control group of 26 healthy adults (16 male, ten female; mean age, 56 years (33 to 84)). The Oxford Hip Score (OHS) and gait analysis using an instrumented treadmill were used preoperatively and more than two years postoperatively to measure the functional change attributable to the intervention.ResultsThe mean OHS improved significantly from 27 to 46 points (p < 0.001) at a mean of 29 months (12 to 60) after HRA. The mean metal ion levels at a mean 32 months (13 to 60) postoperatively were 1.71 (0.77 to 4.83) µg/l (ppb) and 1.77 (0.68 to 4.16) µg/l (ppb) for cobalt and chromium, respectively. When compared with healthy controls, preoperative patients overloaded the contralateral good hip, limping significantly. After HRA, patients walked at high speeds, with symmetrical gait, statistically indistinguishable from healthy controls over almost all characteristics. The control group could only be distinguished by an increased push-off force at higher speeds, which may reflect the operative approach.ConclusionPatients undergoing HRA improved their preoperative gait pattern of a significant limp to a symmetrical gait at high speeds and on inclines, almost indistinguishable from normal controls. HRA with an approved device offers substantial functional gains, almost indistinguishable from healthy controls. Cite this article: Bone Joint J 2019;101-B:1423–1430.

ON THE IDENTITY OF PLATELET FIBRINOGEN WITH PLASMA FIBRINOGEN

1987 ◽  
Author(s):  
H Kaudewitz ◽  
A Henschen ◽  
R E Zimmermann
Keyword(s):  
High Performance ◽  
Reversed Phase ◽  
Plasma Fibrinogen ◽  
Side Chain ◽  
Terminal Sequence ◽  
Hplc Fingerprint ◽  
Amino Terminal ◽  
Chain Composition ◽  
Established Fact ◽  
Amino Terminal Sequence

It is a well established fact that fibrinogen occurs not only in blood plasma but also in the α-granules of the platelets. Recently, it has been shown that fibrinogen is synthesised in the megakaryocytes as well as in the liver. Plasma fibrinogen is derived from the liver, but platelet fibrinogen either exclusively or partially from the megakaryocytes. Conclusive, proteinche-mical evidence for the identity of the fibrinogens from the two biosynthetic sources has previously not been produced. However, the two fibrinogen preparations have been shown to have the same overall peptide chain composition, to be thrombin-clottable and release fibrinopeptides of A- and B-type, and to react with antibodies against plasma fibrinogen. The two preparations differ in the way that platelet fibrinogen lacks the higher-molecular-mass γ-chain variant.The aim of the present investigation was to conduct a detailed proteinchemical comparison between human plasma and platelet fibrinogen. For this purpose, fibrin(ogen)s from the two sources were mercaptolysed, alkylated and the three peptide chains isolated by reversed-phase high-performance liquid chromatography (HPLC). The peptide chains were then analysed directly for amino-terminal sequence and for carboxyterminal sequence by isolation of a terminal fragment. The HPLC-fingerprint patterns of the cyanogen bromide-cleaved chains were compared. The native fibrinogens were also treated with thrombin and the fibrinopeptide type distribution determined by reversed-phase HPLC. The carbohydrate side chain compositions were established by ion-exchange-chromatographic methods after acid hydrolysis. So far no previously unrecognized differences have been observed.

The Kinetic Activation Volumes for the Binding of Iodide to Cobalamin (Vitamin B12) Studied on a High Pressure Laser Temperature Jump Apparatus

1974 ◽  
Vol 52 (6) ◽  
pp. 910-914 ◽  
Author(s):  
Brian B. Hasinoff
Keyword(s):  
High Pressure ◽  
Metal Ion ◽  
Temperature Jump ◽  
Outer Sphere ◽  
Dissociation Rate ◽  
Vitamin B ◽  
Laser Temperature Jump ◽  
Dissociation Rate Constants ◽  
Kinetics Of ◽  
Activated Complex

The relaxation kinetics of the reaction of iodide with cobalamin (vitamin B12) were studied on a high pressure laser temperature jump apparatus in aqueous solution at 25° and ionic strength 0.2 M. Analysis of the pressure dependence of the formation and dissociation rate constants gave their respective volumes of activation to be: ΔVf* = 5.50 ± 0.8 cm3 mol−1 and ΔVd* = 11.5 ± 1.6 cm3 mol−1 The positive activation volume for formation of the complex, ΔVf*, after appropriate correction for the volume change due to formation of an outer sphere complex, is consistent with a dissociative type mechanism in which the metal ion – water bond is stretched in the activated complex.

Five-coordinate iron(II) porphyrins derived from meso-α,β,γ,δ tetraphenylporphin: synthesis, characterization, and coordinating properties

1979 ◽  
Vol 57 (14) ◽  
pp. 1804-1813 ◽  
Author(s):  
Michel Momenteau ◽  
Bernard Loock ◽  
Emile Bisagni ◽  
Michel Rougee
Keyword(s):  
Metal Ion ◽  
Side Chain ◽  
Intramolecular Coordination ◽  
Trans Isomers ◽  
Visible Spectroscopy ◽  
Cis And Trans Isomers ◽  
The Stability ◽  
Heterogeneous Reduction ◽  
Cis And Trans ◽  
Reduced Forms

Meso-α,β,γ,δ, tetraphenylporphin derivatives bearing acrylic (cis and trans isomers) and propionic side chains with a terminal imidazole group have been synthesized. Intermediate compounds obtained during their preparation were characterized by visible spectroscopy and nmr. In non-coordinating solvents (benzene or toluene), the iron(III) complexes of these compounds do not show intramolecular coordination of the terminal base on the metal ion. The reduced forms of the compounds have been obtained from ferric forms by heterogeneous reduction with aqueous dithionite and exhibit optical spectra characteristic of five-coordinate ferrous complexes. The nitrogenous bases and carbon monoxide affinities of the latter have been measured and the results indicate that the 'transinfluence' exerted by the terminal imidazole does not depend greatly on the nature and the structure of the covalent side chain. In contrast the stability of the five-coordinate compounds depends on the side chain (trans acrylic < propionic < cis acrylic) as suggested by the values reported for the replacement constants of the terminal imidazole by 4-cyanopyridine in unsymmetrical six-coordinate derivatives. The stability of these compounds towards oxidation is also reported.

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