scholarly journals Characterization of mutant forms of the quinoprotein methanol dehydrogenase lacking an essential calcium ion

1992 ◽  
Vol 287 (3) ◽  
pp. 709-715 ◽  
Author(s):  
I W Richardson ◽  
C Anthony
Keyword(s):  
Paracoccus Denitrificans ◽  
Molecular Size ◽  
Methanol Dehydrogenase ◽  
Single Atom ◽  
Methylobacterium Extorquens ◽  
Prosthetic Group ◽  
Low Concentrations ◽  
L Proteins ◽  
Group 2 ◽  
Mutant Forms

Methanol dehydrogenase (MDH) from Methylobacterium extorquens, Methylophilus methylotrophus, Paracoccus denitrificans and Hyphomicrobium X all contained a single atom of Ca2+ per alpha 2 beta 2 tetramer. The role of Ca2+ was investigated using the MDH from Methylobacterium extorquens. This was shown to be similar to the MDH from Hyphomicrobium X in having 2 mol of prosthetic group (pyrroloquinoline quinine; PQQ) per mol of tetramer, the PQQ being predominantly in the semiquinone form. MDH isolated from the methanol oxidation mutants MoxA-, K- and L- contained no Ca2+. They were identical with the enzyme isolated from wild-type bacteria with respect to molecular size, subunit configuration, pI, N-terminal amino acid sequence and stability under denaturing conditions (low pH, high urea and high guanidinium chloride) and in the nature and content of the prosthetic group (2 mol of PQQ per mol of MDH). They differed in their lack of Ca2+, the oxidation state of the extracted PQQ (fully oxidized), absence of the semiquinone form of PQQ in the enzyme, reactivity with the suicide inhibitor cyclopropanol and absorption spectrum, which indicated that PQQ is bound differently from that in normal MDH. Incubation of MDH from the mutants in calcium salts led to irreversible time-dependent reconstitution of full activity concomitant with restoration of a spectrum corresponding to that of fully reduced normal MDH. It is concluded that Ca2+ in MDH is directly or indirectly involved in binding PQQ in the active site. The MoxA, K and L proteins may be involved in maintaining a high Ca2+ concentration in the periplasm. It is more likely, however, that they fill a ‘chaperone’ function, stabilizing a configuration of MDH which permits incorporation of low concentrations of Ca2+ into the protein.

scholarly journals Thermal stability of methanol dehydrogenase is altered by the replacement of enzyme-bound Ca2+ with Sr2+

1994 ◽  
Vol 303 (1) ◽  
pp. 141-145 ◽  
Author(s):  
T K Harris ◽  
V L Davidson
Keyword(s):  
Paracoccus Denitrificans ◽  
Double Resonance ◽  
Pyrroloquinoline Quinone ◽  
State Theory ◽  
Methanol Dehydrogenase ◽  
Activation Entropy ◽  
Host Bacterium ◽  
Prosthetic Group ◽  
Electron Nuclear Double Resonance ◽  
Delta G

Methanol dehydrogenase (MEDH) possesses tightly bound Ca2+ in addition to its pyrroloquinoline quinone prosthetic group. Ca2+ was replaced with Sr2+ by growing the host bacterium, Paracoccus denitrificans, in media in which Ca2+ was replaced with Sr2+. At temperatures in the transition region for stability, the rate constants for inactivation of MEDH purified from these cells (Sr-MEDH) were 2-fold lower than those for MEDH. However, Arrhenius plots yielded an activation energy (Ea) of 699 kJ (167 kcal)/mol for MEDH compared with 640 kJ (153 kcal)/mol for Sr-MEDH. Further analysis by transition-state theory yielded values for the activation enthalpy (delta H*) and activation entropy (delta S*) of 696 kJ (166 kcal)/mol and 1.73 kJ (414 cal)/mol per K for MEDH and 637 kJ (152 kcal)/mol and 1.55 kJ (371 cal)/mol per K for Sr-MEDH. The higher rate of inactivation of MEDH than Sr-MEDH at higher temperatures is a consequence of a more favourable net gain in entropy. This positive entropy contribution increases at high temperatures, and reduces the more favourable stability obtained from the enthalpy contribution for the free energy (delta G*) of inactivation. The differences in these thermodynamic data are discussed in relation to the recently determined crystal structure of MEDH as well as 1H electron-nuclear double resonance studies of the influence of Sr2+ substitution on the structure of the pyrroloquinoline quinone-derived radical in MEDH.

scholarly journals Structure of the quinoprotein glucose dehydrogenase of Escherichia coli modelled on that of methanol dehydrogenase from Methylobacterium extorquens

1995 ◽  
Vol 312 (3) ◽  
pp. 679-685 ◽  
Author(s):  
G E Cozier ◽  
C Anthony
Keyword(s):  
Active Site ◽  
Glucose Dehydrogenase ◽  
Ring Structure ◽  
Enzymic Activity ◽  
Methanol Dehydrogenase ◽  
The Novel ◽  
Methylobacterium Extorquens ◽  
Prosthetic Group ◽  
Site Structure ◽  
Proposed Model

The structure of methanol dehydrogenase (MDH) at 0.194 nm (1.94 A) has been used to provide a model structure for part of a membrane quinoprotein glucose dehydrogenase (GDH). The basic superbarrel structure is retained, along with the tryptophan-docking motifs. The active-site regions are similar, but there are important differences, the most important being that GDH lacks the novel disulphide ring structure formed from adjacent cysteines in MDH; in GDH the equivalent region is occupied by His-262. Because of the overall similarities in the active-site region, the mechanism of action of GDH is likely to be similar to that of MDH. The differences in co-ordination to the cation and bonding to the pyrrolo-quinoline quinone (PQQ) in the active site may explain the relative ease of dissociation of the prosthetic group from the holo-GDH. There are considerable differences in the external loops, particularly those involved in formation of the shallow funnel leading to the active site, the configuration of which influences substrate specificity. The proposed model is consistent in many respects with previous proposals for the active-site structure based on the effects of chemical modification on binding of PQQ and enzymic activity.

scholarly journals The role of the novel disulphide ring in the active site of the quinoprotein methanol dehydrogenase from Methylobacterium extorquens

1995 ◽  
Vol 307 (3) ◽  
pp. 735-741 ◽  
Author(s):  
A Avezoux ◽  
M G Goodwin ◽  
C Anthony
Keyword(s):  
Active Site ◽  
Hydrogen Transfer ◽  
Ring Structure ◽  
Methanol Dehydrogenase ◽  
Active Enzyme ◽  
The Novel ◽  
Methylobacterium Extorquens ◽  
Disulphide Bridge ◽  
Prosthetic Group ◽  
Cytochrome Cl

All cysteines in methanol dehydrogenase (MDH) from Methylobacterium extorquens are involved in intra-subunit disulphide bridge formation. One of these is between adjacent cysteine residues which form a novel ring structure in the active site. It is readily reduced, the reduced enzyme being inactive in electron transfer to cytochrome cL. The inactivation is not a result of major structural change or to modification of the prosthetic group pyrrolo-quinoline quinone (PQQ). The reduced enzyme appears to remain active with the artificial electron acceptor phenazine ethosulphate but this is because the dye re-oxidizes the adjacent thiols back to the original disulphide bridge. No free thiols were detected during the reaction cycle with cytochrome cL. Carboxymethylation of the thiols produced by reduction of the novel disulphide ring led to formation of active enzyme. Reconstitution of inactive Ca(2+)-free MDH with Ca2+ led to active enzyme containing the oxidized bridge and reduced quinol, PQQH2, consistent with the conclusion that no hydrogen transfer occurs between these groups in the active site. It is concluded that the disulphide ring in the active site of MDH does not function as a redox component of the reaction. The disulphide ring has no special function in the process of Ca2+ incorporation into the active site. It is suggested that this novel structure might function in the stabilization or protection of the free radical semiquinone form of the prosthetic group (PQQH.) from solvent at the entrance to the active site.

scholarly journals Replacement of enzyme-bound calcium with strontium alters the kinetic properties of methanol dehydrogenase

1994 ◽  
Vol 300 (1) ◽  
pp. 175-182 ◽  
Author(s):  
T K Harris ◽  
V L Davidson
Keyword(s):  
Paracoccus Denitrificans ◽  
Competitive Inhibitor ◽  
Methanol Dehydrogenase ◽  
Native Enzyme ◽  
Kinetic Properties ◽  
Host Bacterium ◽  
Prosthetic Group ◽  
Dependent Activity ◽  
Cyanide Inhibition ◽  
Endogenous Activity

Methanol dehydrogenase (MEDH) possesses tightly bound Ca2+ in addition to its pyrroloquinoline quinone (PQQ) prosthetic group. Ca2+ was replaced with Sr2+ by growing the host bacterium, Paracoccus denitrificans, in media in which Ca2+ was replaced with Sr2+. MEDH, which was purified from these cells (Sr-MEDH), exhibited an increased absorption coefficient for the PQQ chromophore, and displayed certain kinetic properties which were different from those of native MEDH. Native MEDH exhibits an endogenous activity which is not stimulated by substrate and which is inhibited by cyanide. Sr-MEDH exhibited lower endogenous activity which was stimulated by substrate, and was much less sensitive to inhibition by cyanide. The Vmax. for the methanol-dependent activity of Sr-MEDH was 3-fold greater than that of the native enzyme, and the Ks for methanol was altered. Cyanide also acts as an obligatory activator and competitive inhibitor of methanol-dependent activity in native MEDH from P. denitrificans [Harris and Davidson (1993) Biochemistry 32, 4362-4368]. Sr-MEDH exhibited a similar K1 for cyanide inhibition of methanol-dependent activity, but the KA for cyanide activation of this activity was 17-fold greater than that for the native enzyme. The activation energy of Sr-MEDH was 13.4 kJ (3.2 kcal)/mol lower than that of the native enzyme. These data confirm and significantly extend the conclusions from genetic [Richardson and Anthony (1992) Biochem. J. 287, 709-715] and crystallographic [White, Boyd, Mathews, Xia, Dai, Zhang and Davidson (1993) Biochemistry 32, 12955-12958] studies that suggest an apparently unique role for Ca2+ in MEDH compared with other Ca(2+)-dependent proteins and enzymes.

scholarly journals The isocitrate dehydrogenases of Acinetobacter lwoffi. Separation and properties of two nicotinamide–adenine dinucleotide phosphate-linked isoenzymes

1972 ◽  
Vol 130 (1) ◽  
pp. 211-219 ◽  
Author(s):  
Colin H. Self ◽  
P. David J. Weitzman
Keyword(s):  
Molecular Weight ◽  
Ph Dependence ◽  
Gel Filtration ◽  
Deae Cellulose ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Molecular Size ◽  
Ion Exchange Chromatography ◽  
Exchange Chromatography ◽  
Low Concentrations ◽  
Stimulation Of

Two isoenzymes of NADP-linked isocitrate dehydrogenase have been identified in Acinetobacter lwoffi and have been termed isoenzyme-I and isoenzyme-II. The isoenzymes may be separated by ion-exchange chromatography on DEAE-cellulose, by gel filtration on Sephadex G-200, or by zonal ultracentrifugation in a sucrose gradient. Low concentrations of glyoxylate or pyruvate effect considerable stimulation of the activity of isoenzyme-II. The isoenzymes also differ in pH-dependence of activity, kinetic parameters, stability to heat or urea and molecular size. Whereas isoenzyme-I resembles the NADP-linked isocitrate dehydrogenases from other organisms in having a molecular weight under 100000, isoenzyme-II is a much larger enzyme (molecular weight around 300000) resembling the NAD-linked isocitrate dehydrogenases of higher organisms.

scholarly journals Synthesis and Evaluation of [18F]FEtLos and [18F]AMBF3Los as Novel 18F-Labelled Losartan Derivatives for Molecular Imaging of Angiotensin II Type 1 Receptors

Molecules ◽  
2020 ◽  
Vol 25 (8) ◽  
pp. 1872
Author(s):  
Martha Sahylí Ortega Pijeira ◽  
Paulo Sérgio Gonçalves Nunes ◽  
Sofia Nascimento dos Santos ◽  
Zhengxing Zhang ◽  
Arian Pérez Nario ◽  
...  
Keyword(s):  
Angiotensin Ii ◽  
Binding Affinity ◽  
Renin Angiotensin System ◽  
Prosthetic Group ◽  
Positron Emission ◽  
One Step ◽  
Group 2

Losartan is widely used in clinics to treat cardiovascular related diseases by selectively blocking the angiotensin II type 1 receptors (AT1Rs), which regulate the renin-angiotensin system (RAS). Therefore, monitoring the physiological and pathological biodistribution of AT1R using positron emission tomography (PET) might be a valuable tool to assess the functionality of RAS. Herein, we describe the synthesis and characterization of two novel losartan derivatives PET tracers, [18F]fluoroethyl-losartan ([18F]FEtLos) and [18F]ammoniomethyltrifluoroborate-losartan ([18F]AMBF3Los). [18F]FEtLos was radiolabeled by 18F-fluoroalkylation of losartan potassium using the prosthetic group 2-[18F]fluoroethyl tosylate; whereas [18F]AMBF3Los was prepared following an one-step 18F-19F isotopic exchange reaction, in an overall yield of 2.7 ± 0.9% and 11 ± 4%, respectively, with high radiochemical purity (>95%). Binding competition assays in AT1R-expressing membranes showed that AMBF3Los presented an almost equivalent binding affinity (Ki 7.9 nM) as the cold reference Losartan (Ki 1.5 nM), unlike FEtLos (Ki 2000 nM). In vitro and in vivo assays showed that [18F]AMBF3Los displayed a good binding affinity for AT1R-overexpressing CHO cells and was able to specifically bind to renal AT1R. Hence, our data demonstrate [18F]AMBF3Los as a new tool for PET imaging of AT1R with possible applications for the diagnosis of cardiovascular, inflammatory and cancer diseases.

scholarly journals Functional investigation of methanol dehydrogenase-like protein XoxF in Methylobacterium extorquens AM1

Microbiology ◽  
2010 ◽  
Vol 156 (8) ◽  
pp. 2575-2586 ◽  
Author(s):  
Sabrina Schmidt ◽  
Philipp Christen ◽  
Patrick Kiefer ◽  
Julia A. Vorholt
Keyword(s):  
Growth Parameters ◽  
Methanol Dehydrogenase ◽  
Plant Colonization ◽  
Kinetic Properties ◽  
Wild Type ◽  
Methylobacterium Extorquens ◽  
Experimental Conditions ◽  
Dependent Protein ◽  
One Carbon Metabolism ◽  
Functional Investigation

Methanol dehydrogenase-like protein XoxF of Methylobacterium extorquens AM1 exhibits a sequence identity of 50 % to the catalytic subunit MxaF of periplasmic methanol dehydrogenase in the same organism. The latter has been characterized in detail, identified as a pyrroloquinoline quinone (PQQ)-dependent protein, and shown to be essential for growth in the presence of methanol in this methylotrophic model bacterium. In contrast, the function of XoxF in M. extorquens AM1 has not yet been elucidated, and a phenotype remained to be described for a xoxF mutant. Here, we found that a xoxF mutant is less competitive than the wild-type during colonization of the phyllosphere of Arabidopsis thaliana, indicating a function for XoxF during plant colonization. A comparison of the growth parameters of the M. extorquens AM1 xoxF mutant with those of the wild-type during exponential growth revealed a reduced methanol uptake rate and a reduced growth rate for the xoxF mutant of about 30 %. Experiments with cells starved for carbon revealed that methanol oxidation in the xoxF mutant occurs less rapidly compared with the wild-type, especially in the first minutes after methanol addition. A distinct phenotype for the xoxF mutant was also observed when formate and CO2 production were measured after the addition of methanol or formaldehyde to starved cells. The wild-type, but not the xoxF mutant, accumulated formate upon substrate addition and had a 1 h lag in CO2 production under the experimental conditions. Determination of the kinetic properties of the purified enzyme showed a conversion capacity for both formaldehyde and methanol. The results suggest that XoxF is involved in one-carbon metabolism in M. extorquens AM1.

scholarly journals Cytochalasins inhibit nuclei-induced actin polymerization by blocking filament elongation.

1980 ◽  
Vol 84 (2) ◽  
pp. 455-460 ◽  
Author(s):  
D C Lin ◽  
K D Tobin ◽  
M Grumet ◽  
S Lin
Keyword(s):  
Binding Sites ◽  
Actin Polymerization ◽  
Cytochalasin B ◽  
Molecular Size ◽  
Muscle Actin ◽  
Competitive Displacement ◽  
Low Concentrations ◽  
Relative Affinity ◽  
Cytochalasin E ◽  
Low Ionic Strength

Polylysine was found to induce polymerization of muscle actin in a low ionic strength buffer containing 0.4 mM MgCl2. The rate of induced polymerization was dependent on the amount and on the molecular size of the polylysine added. A similar effect was obtained by adding actin nuclei (containing about 2-4 actin subunits) cross-linked by p-N,N'-phenylenebismaleimide to G-actin under the same conditions, suggesting that the effect of polylysine is due to promotion of the formation of actin nuclei. Polymerization induced by polylysine and by cross-linked actin nuclei was inhibited by low concentrations (10(-8)-10(-6)M) of cytochalasins. Binding experiments showed that actin filaments, but not actin monomers, contained high-affinity binding sites for [3H]cytochalasin B (one site per 600 actin monomers). The relative affinity of several cytochalasins for these sites (determined by competitive displacement of [3H]dihydrocytochalasin B) was: cytochalasin D greater than cytochalasin E approximately equal to dihydrocytochalasin B. The results of this study suggest that cytochalasins inhibit nuclei-induced actin polymerization by binding to highly specific sites at the point of monomer addition, i.e., the elongation site, in actin nuclei and filaments.

scholarly journals The prosthetic group of methanol dehydrogenase. Purification and some of its properties

1980 ◽  
Vol 187 (1) ◽  
pp. 221-226 ◽  
Author(s):  
J A Duine ◽  
J Frank
Keyword(s):  
Methanol Dehydrogenase ◽  
Water Soluble ◽  
Soluble Nitrogen ◽  
Prosthetic Group ◽  
Whole Cells ◽  
Group A

Methanol dehydrogenases isolated from bacteria belonging to different classes of methylotrophs contain the same prosthetic group. A procedure for its purification from whole cells is given. The reduced and oxidized form of the enzyme from Hyphomicrobium X and those of the isolated group are compared and it is concluded that the latter indeed functions in the enzyme. Further evidence is presented that the prosthetic group is not a pterine or lumazine derivative, but a water-soluble nitrogen-containing quinone.

Sign in / Sign up

Export Citation Format

Share Document