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Brian Bennett

Publications and source records attributed to Brian Bennett.

25 records · Page 2Linked to original sources
PubMed2004

Mononuclear nitrogen/sulfur-ligated cobalt(II) methoxide complexes: structural, EPR, paramagnetic 1H NMR, and electrochemical investigations.

The first examples of mononuclear nitrogen/sulfur-ligated Co(II) alkoxide complexes, species of relevance to a reactive intermediate observed for Co(II)-substituted liver alcohol dehydrogenase, have been isolated and characterized by multiple methods including X-ray crystallography, EPR, paramagnetic (1)H NMR, and cyclic voltammetry.

Alcohol Dehydrogenase↗
PubMed2003

Substrate specificity, metal binding properties, and spectroscopic characterization of the DapE-encoded N-succinyl-L,L-diaminopimelic acid desuccinylase from Haemophilus influenzae.

The catalytic and structural properties of divalent metal ion cofactor binding sites in the dapE-encoded N-succinyl-L,L-diaminopimelic acid desuccinylase (DapE) from Haemophilus influenzae were investigated. Co(II)-substituted DapE enzyme was 25% more active than the Zn(II)-loaded form of the enzyme. Interestingly, Mn(II) can activate DapE, but only to approximately 20% of the Zn(II)-loaded enzyme. The order of the observed k(cat) values are Co(II) > Zn(II) > Cd(II) > Mn(II) >Ni(II) approximately equal Cu(II) approximately equal Mg(II). DapE was shown to only hydrolyze L,L-N-succinyl-diaminopimelic acid (L,L-SDAP) and was inactive toward D,L-, L,D-, and D,D-SDAP. DapE was also inactive toward several acetylated amino acids as well as D,L-succinyl aminopimelate, which differs from the natural substrate, L,L-SDAP, by the absence of the amine group on the amino acid side chain. These data imply that the carboxylate of the succinyl moiety and the amine form important interactions with the active site of DapE. The affinity of DapE for one versus two Zn(II) ions differs by nearly 2.2 x 10(3) times (K(d1) = 0.14 microM vs K(d2) = 300 microM). In addition, an Arrhenius plot was constructed from k(cat) values measured between 16 and 35 degrees C and was linear over this temperature range. The activation energy for [ZnZn(DapE)] was found to be 31 kJ/mol with the remaining thermodynamic parameters calculated at 25 degrees C being DeltaG(++) = 64 kJ/mol, DeltaH(++) = 28.5 kJ/mol, and DeltaS(++) = -119 J mol(-1) K(-1). Electronic absorption and EPR spectra of [Co_(DapE)] and [CoCo(DapE)] indicate that the first Co(II) binding site is five-coordinate, while the second site is octahedral. In addition, any spin-spin interaction between the two Co(II) ions in [CoCo(DapE)] is very weak. The kinetic and spectroscopic data presented herein suggest that the DapE from H. influenzae has similar divalent metal binding properties to the aminopeptidase from Aeromonas proteolytica (AAP), and the observed divalent metal ion binding properties are discussed with respect to their catalytic roles in SDAP hydrolysis.

Acetylation↗
PubMed2002

Structurally distinct active sites in the copper(II)-substituted aminopeptidases from Aeromonas proteolytica and Escherichia coli.

The aminopeptidase from Aeromonas proteolytica (AAP) was titrated with copper, which bound sequentially at two distinct sites. Both the mono- and disubstituted forms of AAP exhibited catalytic hyperactivity relative to the native dizinc enzyme. Monosubstituted AAP exhibited an axial Cu(II) EPR spectrum with slight pH dependence: at pH 6.0 g(parallel) = 2.249, g( perpendicular ) = 2.055, and A(parallel)((63/65)Cu) = 1.77 x 10(-)(2) cm(-)(1), whereas at pH 9.65 g(parallel) = 2.245, g( perpendicular ) = 2.056, and A(parallel)((63/65)Cu) = 1.77 x 10(-)(2) cm(-)(1). These data indicate oxygen and nitrogen ligation of Cu. AAP further substituted with copper exhibited a complex signal with features around g approximately 2 and 4. The features at g approximately 4 were relatively weak in the B(0) perpendicular B(1) (perpendicular) mode EPR spectrum but were intense in the B(0) parallel B(1) (parallel) mode spectrum. The g approximately 2 region of the perpendicular mode spectrum exhibited two components, one corresponding to mononuclear Cu(II) with g(parallel) = 2.218, g( perpendicular ) = 2.023, and A(parallel)((63/65)Cu) = 1.55 x 10(-)(2) cm(-)(1) and likely due to adventitious binding of Cu(II) to a site distant from the active site. Excellent simulations were obtained for the second component of the spectrum assuming that two Cu(II) ions experience dipolar coupling corresponding to an inter-copper distance of 5 A with the two Cu(II) g(z)() directions parallel to each other and at an angle of approximately 17 degrees to the inter-copper vector (H = betaB.g(CuA).S(CuA) + betaB.g(CuB).S(CuB) + [S.A.I](CuA) + [S.A.I](CuB) + [S(CuA).J.S(CuB)]; g(parallel(CuA,CuB)) = 2.218, g( perpendicular )((CuA,CuB)) = 2.060; A(parallel(CuA,CuB))((63/65)Cu) = 1.59 x 10(-)(2) cm(-)(1), J(isotropic) = 50 cm(-)(1), r(Cu)(-)(Cu) = 4.93 A, and chi = 17 degrees ). The exchange coupling between the two copper ions was found to be ferromagnetic as the signals exhibited Curie law temperature dependence. The Cu-Cu distance of approximately 5 A indicated by EPR was significantly higher than the inter-zinc distance of 3.5 A in the native enzyme, and the dicopper species therefore represents a novel dinuclear site capable of catalysis of hydrolysis. In contrast to AAP, the related methionyl aminopeptidase from Escherichia coli (EcMetAP) was found to bind only one Cu(II) ion despite possessing a dinuclear binding site motif. A further difference was the marked pH dependence of the signal in EcMetAP, suggestive of a change in ligation. The structural motifs of these two Cu(II)-substituted aminopeptidases provide important insight into the observed catalytic activity.

Aeromonas↗
PubMed2002

Simvastatin promotes atherosclerotic plaque stability in apoE-deficient mice independently of lipid lowering.

OBJECTIVE: This study sought to determine whether simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, has stabilizing effects on vulnerable atherosclerotic plaques that are independent of their lipid-lowering capabilities. METHODS AND RESULTS: Simvastatin (50 mg/kg per day) was administered to 30-week-old apolipoprotein E-deficient mice exhibiting advanced unstable atherosclerotic lesions within the innominate/brachiocephalic artery. Simvastatin was administered in the chow to separate groups of mice for 6, 12, 18, or 24 weeks. Simvastatin significantly increased serum cholesterol after 12, 18, and 24 weeks of treatment. The average cross-sectional area of atherosclerotic lesion increased in the innominate artery after 12 and 24 weeks of treatment, concomitant with the increase in serum cholesterol. However, histological analysis of sections of the innominate artery stained with Movat and von Kossa stains demonstrated a 49% reduction in the frequency of intraplaque hemorrhage and a 56% reduction in the frequency of calcification, both markers of advanced and unstable atherosclerotic plaques. CONCLUSIONS: These data suggest that despite an increase in serum cholesterol and lesion size, simvastatin has stabilizing effects on advanced atherosclerotic lesions.

Animals↗
PubMed1998

Synthesis, Molecular Structure, and Reactivity of Dinuclear Copper(II) Complexes with Carboxylate-Rich Coordination Environments.

The dinucleating ligand N,N'-(2-hydroxy-5-methyl-1,3-xylylene)bis(N-(carboxymethyl)glycine) (CH(3)HXTA) has been used to synthesize the dinuclear Cu(II) bis(pyridine) complex Na[Cu(2)(CH(3)HXTA)(Py)(2)].1.5(1,4-dioxane) (Na(1)): triclinic space group P&onemacr; (a = 12.550(3) Å, b = 13.413(3) Å, c = 13.540(4) Å, alpha = 117.12(2) degrees, beta = 104.70 (2) degrees, and gamma = 92.13(2) degrees ). The structure shows two distinct distorted square pyramidal Cu(II) centers with each Cu(II) ion bound by two carboxylate oxygen atoms, one amine nitrogen atom, a phenolate oxygen atom, and one pyridine nitrogen atom. The Cu--Cu separation is 3.531 Å, and the Cu1-O1-Cu2 angle is 123.7 degrees. The phenyl ring of the CH(3)HXTA ligand is twisted relative to the Cu1-O1-Cu2 plane, and the resulting dihedral angle is 44.2 degrees. The electronic absorption spectrum of 1 in aqueous solution at pH 3 suggests a shift toward trigonal bipyramidal Cu(II) coordination in solution. Spectral titration of Na[Cu(2)(CH(3)HXTA)(H(2)O)(2)] with L (where L = pyridine or sodium cyanide) results in complexes with terminal L groups. These exogenous ligands appear to bind in a positive cooperative stepwise fashion. Variable-temperature magnetic susceptibility data for 1 indicate that the Cu(II) ions are antiferromagnetically coupled (-2J = 168 cm(-)(1)). X-band EPR spectra of an aqueous solution of 1 shows isotropic signals with g = 2.14, while a powdered sample of 1 provides no EPR spectrum. A DeltaM(s) = 2 transition at g = approximately 4.5, expected for weakly magnetically coupled Cu(II) ions, is not observed for powdered samples but is observed for a methanolic solution sample of 1. On the basis of these data, the two Cu(II) ions are antiferromagnetically coupled in the solid state but due to a coordination geometry change become weakly ferromagnetically or antiferromagnetically coupled in solution. (1)H NMR studies on a methanol solution of 1 are consistent with weak spin-coupling in solution.

Journal Article↗