A Study of Manganous Complexes by Paramagnetic Resonance Absorption

Cohn, Mildred; Townsend, Jonathan

doi:10.1038/1731090b0

Cited by 235 publications

(127 citation statements)

References 3 publications

Supporting

Mentioning

124

Contrasting

Order By: Relevance

“…In work pioneered by the research group of Mildred Cohn [48][49][50][51][52][53][54] at the University of Pennsylvania, continuous-wave (CW) EPR spectroscopy was shown to be highly adept at probing the geometric and electronic structure of the Mn(II) ion present in ATP-dependent kinases. Through analysis of spectral changes upon the addition of natural abundance and isotopically labeled substrate, product, or inhibitor, they gained significant insight into substrate-induced active site rearrangements [51] and were able to propose models of the reaction transition state.…”

Section: Past Studiesmentioning

confidence: 99%

Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

et al. 2007

View full text Add to dashboard Cite

Electron paramagnetic resonance studies at multiple frequencies (MF EPR) can provide detailed electronic structure descriptions of unpaired electrons in organic radicals, inorganic complexes, and metalloenzymes. Analysis of these properties aids in the assignment of the chemical environment surrounding the paramagnet and provides mechanistic insight into the chemical reactions in which these systems take part. Herein, we present results from pulsed EPR studies performed at three different frequencies (9, 31, and 130 GHz) on [Mn(II)(H 2 O) 6 ] 2+ , Mn(II) adducts with the nucleotides ATP and GMP, and the Mn(II)-bound form of the hammerhead ribozyme (MnHH). Through line shape analysis and interpretation of the zero-field splitting values derived from successful simulations of the corresponding continuous-wave and field-swept echodetected spectra, these data are used to exemplify the ability of the MF EPR approach in distinguishing the nature of the first ligand sphere. A survey of recent results from pulsed EPR, as well as pulsed electron-nuclear double resonance and electron spin echo envelope modulation spectroscopic studies applied to Mn(II)-dependent systems, is also presented. Mn-Containing Biological SystemsManganese operates as a cofactor in numerous proteins, serving both catalytic and structural roles [1][2][3][4]. Many Mn-dependent enzymes take advantage o f the rich redox chemistry available to the metal, accessing the +2, +3, +4, and perhaps even the +5 oxidation states during their turnover. For example, Mn-superoxide dismutase (MnSOD), which detoxifies the cell of the superoxide radical , cycles between the Mn(II) and Mn(III) oxidation states via the ping-pong type mechanism shown below [5][6][7][8][9].(1a) (1b) Other examples of such mononuclear redox-active enzymes include the manganese peroxidase responsible for lignin degradation by white-rot fungus [10][11][12]; a unique Mndependent form of lipoxygenase [13][14][15][16]; oxalate decarboxylase [17,18]; as well as an extradiol catechol dioxygenase [19][20][21]. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptIn order to help minimize kinetic and thermodynamic penalties associated with electron transfer events and the execution of chemical reactions, two or more metal centers can be coupled together to provide active sites capable of conducting multiple electrons while still operating within a physiologically accessible range of reduction potentials [22]. Only three such examples of redox-active polynuclear Mn enzymes are known: Mn-catalase that disproportionates hydrogen peroxide [23][24][25][26]; a Mn form of ribonucleotide reductase (Mn-RNR) [27,28]; and, arguably the most recognized Mn-dependent enzyme, the photosynthetic core of green plants, algae, and certain cyanobacteria termed photosystem II (PSII) [29,30]. Through a series of photoinitiated electron transfer events, oxidizing equivalents are stored on the tetranuclear Mn core of PSII -the oxygen-evolving complex (OEC) -which then extracts four electr...

show abstract

Section: Past Studiesmentioning

confidence: 99%

Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

et al. 2007

View full text Add to dashboard Cite

show abstract

“…To determine the number of Mn 2ϩ tightly bound to ␥-GCS and their respective dissociation constants, ␥-GCS was titrated into a solution of 100 M MnCl 2 , and the change in concentration of free Mn 2ϩ was determined from the decrease in the peak to peak amplitude of the low field line of the room temperature free Mn 2ϩ EPR spectra (44). Representative spectra are shown in the Fig.…”

Section: Epr Studies With Mnmentioning

confidence: 99%

Escherichia coli γ-Glutamylcysteine Synthetase

Kelly¹,

Antholine²,

Griffith³

2002

Journal of Biological Chemistry

View full text Add to dashboard Cite

␥-Glutamylcysteine synthetase (␥-GCS, glutamate-cysteine ligase), which catalyzes the first and rate-limiting step in glutathione biosynthesis, is present in many prokaryotes and in virtually all eukaryotes. Although all eukaryotic ␥-GCS isoforms examined to date are rapidly inhibited by buthionine sulfoximine (BSO), most reports indicate that bacterial ␥-GCS is resistant to BSO. We have confirmed the latter finding with Escherichia coli ␥-GCS under standard assay conditions, showing both decreased initial binding affinity for BSO and a reduced rate of BSO-mediated inactivation compared with mammalian isoforms. We also find that substitution of Mn 2؉for Mg 2؉ in assay mixtures increases both the initial binding affinity of BSO and the rate at which BSO causes mechanism-based inactivation. Similarly, the specificity of E. coli ␥-GCS for its amino acid substrates is broadened in the presence of Mn 2؉ , and the rate of reaction for some very poor substrates is improved. These results suggest that divalent metal ions have a role in amino acid binding to E. coli ␥-GCS. Electron paramagnetic resonance (EPR) studies carried out with

show abstract

“…1 was derived by measuring the amplitude of EPR signals (sum of six lines) for the equilibrium amount of unbound Mn(I1) in solution in the presence of the free form of ACP-SH. This procedure for EPR data manipulation was described earlier [17,181. A small amount of the reducing agent dithiothreitol (0.1 mM) was added to the solution to ensure that ACP-SH remained in the free sulfhydryl form.…”

Section: Acp-shmentioning

confidence: 99%

Divalent cation biding to reduced and octanoyl acyl‐carrier protein

Tener

Mayo

1990

European Journal of Biochemistry

View full text Add to dashboard Cite

Mn(I1) EPR binding studies with reduced acyl-carrier protein (ACP-SH) strongly suggest the presence of two relatively high-affinity manganese-binding sites (average &/site z 80 pM) at physiological pH. Lowering the pH or titrating with sodium chloride reduces the average number of bound divalent cations and decreases the binding affinity. This is consistent with the idea that anionic ligand(s), e. g. the carboxylate of glutamic or aspartic acid, on the protein are involved in manganese ion coordination. At pH values above 8.0, binding affinity is also reduced, whereas the average number of bound metal ions increases to about five at pH 8.5. By interacting weakly with divalent cations (average &/site z 1 mM), octanoyl acyl-carrier protein (OcoACP) exhibits dramatically different metal-ion-binding properties compared to ACP-SH. Calcium and magnesium can compete in either ACP species for manganese binding. Photochemically-induced dynamic nuclear polarisation 'H-NMR experiments strongly suggest that ACP-SH and OcoACP undergo at pH-induced conformational change between pH 5.5 and pH 7.0, and that divalent cations stabilize the protein against such pH-induced structural perturbations.Fatty acid biosynthesis is a central biochemical pathway involving several enzymatic steps [I -31. Acyl-carrier proteins (ACP) are coenzymes which function in acyl-group-transfer reactions, chain-elongation reactions by successive addition of two-carbon fragments from malonyl-CoA, and as anchors for reduction and dehydration reactions that ultimately lead to a saturated fatty acid [2]. Since ACP is active in a variety of differing acylated states involved in various enzymatic reactions and, therefore, with a number of different enzymes, it is likely that ACP has the ability to modify or fine-tune its conformation to interact efficiently in all situations and, perhaps, even effect regulation of fatty acid biosynthesis.The ability to isolate ACP from Escherichiu coli as a soluble protein, and not as part of a tightly associated protein complex found in higher organisms, has made it the most studied among all ACPs which, in any event, possess a high degree of sequence similarity [2]. Of the 77 amino acids (8847 Da) found in E. coli ACP, 22 are acidic (glutamic and aspartic acid residues) and six are basic (lysine, arginine and histidine residues) [4, 51. This gives the protein an net charge of -16. To date, a secondary backbone structure for E. coli ACP-SH (reduced) has been derived from two-dimensional 'H-NMR studies [6]. The following segments are proposed to be helical: residues 3 -15,37 -51,56 -63 and 65 -75; these are connected by extended chain and p-turn structure. The three-dimensional structure of ACP-SH, determined by NMR pseudo-energy and distance geometry calculations [7], have identified three helical regions: residues 3-14, 37-51 and 65-75, which run anti-parallel to each other. Octanoyl-ACP, an S-acylated species of ACP, shows a similar overall conformation with Correspondence to K .

show abstract

A Study of Manganous Complexes by Paramagnetic Resonance Absorption

Cited by 235 publications

References 3 publications

Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

Escherichia coli γ-Glutamylcysteine Synthetase

Divalent cation biding to reduced and octanoyl acyl‐carrier protein

Contact Info

Product

Resources

About