EPR Definition of the Non-Heme Ferric Active Sites of Mammalian 15-Lipoxygenases: Major Spectral Differences Relative to Human 5-Lipoxygenases and Plant Lipoxygenases and Their Ligand Field Origin

1995 ◽  
Vol 117 (28) ◽  
pp. 7422-7427 ◽  
Author(s):  
Yan Zhang ◽  
Qing-Fen Gan ◽  
Elizabeth G. Pavel ◽  
Elliott Sigal ◽  
Edward I. Solomon
Keyword(s):  
Active Sites ◽  
Ligand Field ◽  
Definition Of ◽  
Plant Lipoxygenases

Spectroscopic Definition of the Copper Active Sites in Mordenite: Selective Methane Oxidation

2015 ◽  
Vol 137 (19) ◽  
pp. 6383-6392 ◽  
Author(s):  
Pieter Vanelderen ◽  
Benjamin E. R. Snyder ◽  
Ming-Li Tsai ◽  
Ryan G. Hadt ◽  
Julie Vancauwenbergh ◽  
...  
Keyword(s):  
Methane Oxidation ◽  
Active Sites ◽  
Definition Of

scholarly journals Spectroscopic Definition of the Ferroxidase Site in M Ferritin: Comparison of Binuclear Substrate vs Cofactor Active Sites

2008 ◽  
Vol 130 (29) ◽  
pp. 9441-9450 ◽  
Author(s):  
Jennifer K. Schwartz ◽  
Xiaofeng S. Liu ◽  
Takehiko Tosha ◽  
Elizabeth C. Theil ◽  
Edward I. Solomon
Keyword(s):  
Active Sites ◽  
Definition Of

[NiFe]-hydrogenases: spectroscopic and electrochemical definition of reactions and intermediates

2005 ◽  
Vol 363 (1829) ◽  
pp. 937-954 ◽  
Author(s):  
Fraser A Armstrong ◽  
Simon P.J Albracht
Keyword(s):  
Fuel Cells ◽  
Active Sites ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Energy Technologies ◽  
Highly Active ◽  
Definition Of ◽  
Micro Organisms ◽  
Electron Paramagnetic

Production and usage of di-hydrogen, H 2 , in micro-organisms is catalysed by highly active, ‘ancient’ metalloenzymes known as hydrogenases. Based on the number and identity of metal atoms in their active sites, hydrogenases fall into three main classes, [NiFe]-, [FeFe]- and [Fe]-. All contain the unusual ligand CO (and in most cases CN − as well) making them intriguing examples of ‘organometallic’ cofactors. These ligands render the active sites superbly ‘visible’ using infrared spectroscopy, which complements the use of electron paramagnetic resonance spectroscopy in studying mechanisms and identifying intermediates. Hydrogenases are becoming a focus of attention for research into future energy technologies, not only H 2 production but also H 2 oxidation in fuel cells. Hydrogenases immobilized on electrodes exhibit high electrocatalytic activity, providing not only an important new technique for their investigation, but also a basis for novel fuel cells either using the enzyme itself, or inspired synthetic catalysts. Favourable comparisons have been made with platinum electrocatalysts, an advantage of enzymes being their specificity for H 2 and tolerance of CO. A challenge for exploiting hydrogenases is their sensitivity to O 2 , but some organisms are known to produce enzymes that overcome this problem by subtle alterations of the active site and gas access channels.

scholarly journals Structural definition of the lysine swing in Arabidopsis thaliana PDX1: Intermediate channeling facilitating vitamin B6 biosynthesis

2016 ◽  
Vol 113 (40) ◽  
pp. E5821-E5829 ◽  
Author(s):  
Graham C. Robinson ◽  
Markus Kaufmann ◽  
Céline Roux ◽  
Teresa B. Fitzpatrick
Keyword(s):  
Arabidopsis Thaliana ◽  
Active Site ◽  
Active Sites ◽  
De Novo ◽  
Primed State ◽  
Coenzyme Form ◽  
Ammonia Addition ◽  
Definition Of ◽  
Complex Chemistry ◽  
Structural Definition

Vitamin B6 is indispensible for all organisms, notably as the coenzyme form pyridoxal 5′-phosphate. Plants make the compound de novo using a relatively simple pathway comprising pyridoxine synthase (PDX1) and pyridoxine glutaminase (PDX2). PDX1 is remarkable given its multifaceted synthetic ability to carry out isomerization, imine formation, ammonia addition, aldol-type condensation, cyclization, and aromatization, all in the absence of coenzymes or recruitment of specialized domains. Two active sites (P1 and P2) facilitate the plethora of reactions, but it is not known how the two are coordinated and, moreover, if intermediates are tunneled between active sites. Here we present X-ray structures of PDX1.3 from Arabidopsis thaliana, the overall architecture of which is a dodecamer of (β/α)8 barrels, similar to the majority of its homologs. An apoenzyme structure revealed that features around the P1 active site in PDX1.3 have adopted inward conformations consistent with a catalytically primed state and delineated a substrate accessible cavity above this active site, not noted in other reported structures. Comparison with the structure of PDX1.3 with an intermediate along the catalytic trajectory demonstrated that a lysine residue swings from the distinct P2 site to the P1 site at this stage of catalysis and is held in place by a molecular catch and pin, positioning it for transfer of serviced substrate back to P2. The study shows that a simple lysine swinging arm coordinates use of chemically disparate sites, dispensing with the need for additional factors, and provides an elegant example of solving complex chemistry to generate an essential metabolite.

scholarly journals Aerobic oxidation of hydrocarbons in Mn-doped aluminophosphates: a computational perspective to understand mechanism and selectivity

2012 ◽  
Vol 468 (2143) ◽  
pp. 2053-2069 ◽  
Author(s):  
Furio Corà ◽  
Luis Gómez-Hortigüela ◽  
C. Richard A. Catlow
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Aerobic Oxidation ◽  
Periodic Boundary Conditions ◽  
Atomic Level ◽  
Functional Theory ◽  
Oxidation Of Hydrocarbons ◽  
Structural Environment ◽  
Definition Of ◽  
Mn Doped

We discuss the mechanism and energetics for the aerobic oxidation of hydrocarbons catalysed by Mn-doped nanoporous aluminophosphates with the AFI structure (Mn-APO-5), obtained computationally using electronic structure techniques. Calculations have been performed employing hybrid exchange density functional theory methods under periodic boundary conditions. The active sites of the catalyst are tetrahedral Mn ions isomorphously replacing Al in the microporous crystalline framework of the AlPO host. Since all Al sites in AFI are symmetry equivalent, all Mn dopants are in an identical chemical and structural environment, and hence satisfy the definition of a single-site heterogeneous catalyst. We focus in particular on the atomic-level origin of selectivity in this catalytic reaction.

scholarly journals A ligand field chemistry of oxygen generation by the oxygen-evolving complex and synthetic active sites

2007 ◽  
Vol 363 (1494) ◽  
pp. 1293-1303 ◽  
Author(s):  
Theodore A Betley ◽  
Yogesh Surendranath ◽  
Montana V Childress ◽  
Glen E Alliger ◽  
Ross Fu ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Active Sites ◽  
Ligand Field ◽  
Oxygen Evolving Complex ◽  
Oxygen Generation ◽  
Bond Forming ◽  
Oxygen Oxygen ◽  
Functional Models ◽  
High Valent ◽  
Oxygen Evolving

Oxygen–oxygen bond formation and O 2 generation occur from the S 4 state of the oxygen-evolving complex (OEC). Several mechanistic possibilities have been proposed for water oxidation, depending on the formal oxidation state of the Mn atoms. All fall under two general classifications: the AB mechanism in which nucleophilic oxygen (base, B) attacks electrophilic oxygen (acid, A) of the Mn 4 Ca cluster or the RC mechanism in which radical-like oxygen species couple within OEC. The critical intermediate in either mechanism involves a metal oxo, though the nature of this oxo for AB and RC mechanisms is disparate. In the case of the AB mechanism, assembly of an even-electron count, high-valent metal-oxo proximate to a hydroxide is needed whereas, in an RC mechanism, two odd-electron count, high-valent metal oxos are required. Thus the two mechanisms give rise to very different design criteria for functional models of the OEC active site. This discussion presents the electron counts and ligand geometries that support metal oxos for AB and RC O–O bond-forming reactions. The construction of architectures that bring two oxygen functionalities together under the purview of the AB and RC scenarios are described.

Introductory paper

1966 ◽  
Vol 24 ◽  
pp. 3-5
Author(s):  
W. W. Morgan
Keyword(s):  
Line Intensity ◽  
Classification Scheme ◽  
Two Dimensional ◽  
Spectral Classification ◽  
Dimensional Array ◽  
Rr Lyrae ◽  
Metallic Line ◽  
Introductory Paper ◽  
Parameter Varying ◽  
Definition Of

1. The definition of “normal” stars in spectral classification changes with time; at the time of the publication of theYerkes Spectral Atlasthe term “normal” was applied to stars whose spectra could be fitted smoothly into a two-dimensional array. Thus, at that time, weak-lined spectra (RR Lyrae and HD 140283) would have been considered peculiar. At the present time we would tend to classify such spectra as “normal”—in a more complicated classification scheme which would have a parameter varying with metallic-line intensity within a specific spectral subdivision.

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