scholarly journals Cytochrome b-562 from Acinetobacter calcoaceticus L.M.D. 79.41. Its characteristics and role as electron acceptor for quinoprotein glucose dehydrogenase

1988 ◽  
Vol 254 (1) ◽  
pp. 131-138 ◽  
Author(s):  
P Dokter ◽  
J E van Wielink ◽  
M A G van Kleef ◽  
J A Duine
Keyword(s):  
Cytochrome B ◽  
Electron Acceptor ◽  
Glucose Dehydrogenase ◽  
Acinetobacter Calcoaceticus ◽  
Primary Electron ◽  
Reduced Form ◽  
Alpha Band ◽  
Absorption Bands ◽  
Midpoint Potential ◽  
Triton X

A soluble cytochrome b was purified from Acinetobacter calcoaceticus L.M.D. 79.41. On the basis of the alpha-band maximum of a reduced preparation, measured at 25 degrees C, it is designated as cytochrome b-562. This cytochrome is a basic monomeric protein (pI 10.2; Mr 18,000), containing one protohaem group per molecule. The reduced form, at 25 degrees C, showed absorption bands at 428, 532 and 562 nm. At 77 K the alpha-band shifted to 560 nm (with a shoulder at 558 nm). The reduced cytochrome did not react with CO. Cytochrome b-562 is most probably (loosely) attached to the outside of the cytoplasmic membrane, since substantial amounts of it, equimolar to quinoprotein glucose dehydrogenase (GDH), were present in the culture medium when cells were grown in the presence of low concentrations of Triton X-100. The midpoint potential at pH 7.0 was found to be +170 mV, a value that was lowered to +145 mV by the presence of GDH. Since the GDH was shown to have a midpoint potential of +50 mV, cytochrome b-562 could function as the natural primary electron acceptor. Arguments to substantiate this view and to propose a role of ubiquinone-9 as electron acceptor for cytochrome b-562 are presented.

scholarly journals Purification and characterization of quinoprotein glucose dehydrogenase from Acinetobacter calcoaceticus L.M.D. 79.41

1986 ◽  
Vol 239 (1) ◽  
pp. 163-167 ◽  
Author(s):  
P Dokter ◽  
J Frank ◽  
J A Duine
Keyword(s):  
Electron Acceptor ◽  
Glucose Dehydrogenase ◽  
Substrate Inhibition ◽  
Acinetobacter Calcoaceticus ◽  
Reaction Rates ◽  
Reduced Form ◽  
Initial Reaction ◽  
Type I ◽  
Ph Optimum ◽  
Enzyme Form

Quinoprotein glucose dehydrogenase (EC 1.1.99.17) from Acinetobacter calcoaceticus L.M.D. 79.41 was purified to homogeneity. It is a basic protein with an isoelectric point of 9.5 and an Mr of 94,000. Denaturation yields two molecules of PQQ/molecule and a protein with an Mr of 48000, indicating that the enzyme consists of two subunits, which are probably identical because even numbers of aromatic amino acids were found. The oxidized enzyme form has an absorption maximum at 350 nm, and the reduced form, obtained after the addition of glucose, at 338 nm. Since double-reciprocal plots of initial reaction rates with various concentrations of glucose or electron acceptor show parallel lines, and substrate inhibition is observed for glucose as well as for electron acceptor at high concentrations, a ping-pong kinetic behaviour with the two reactants exists. From the plots, Km values for glucose and Wurster's Blue of 22 mM and 0.78 mM respectively, and a Vmax. of 7.730 mumol of glucose oxidized/min per mg of protein were derived. The enzyme shows a broad substrate specificity for aldose sugars. Cationic electron acceptors are active in the assay, anionic acceptors are not. A pH optimum of 9.0 was found with Wurster's Blue and 6.0 with 2,6-dichlorophenol-indophenol. Two types of quinoprotein glucose dehydrogenases seem to exist: type I enzymes are acidic proteins from which PQQ can be removed by dialysis against EDTA-containing buffers (examples are found in Escherichia coli, Klebsiella aerogenes and Pseudomonas sp.); type II enzymes are basic proteins from which PQQ is not removed by dialysis against EDTA-containing buffers (examples are found in A. calcoaceticus and Gluconobacter oxydans).

Occurrence of c-Type Cytochrome in Mycobacterium lepraemurium

1974 ◽  
Vol 52 (11) ◽  
pp. 991-996 ◽  
Author(s):  
M. Ishaque ◽  
L. Kato
Keyword(s):  
Absorption Spectrum ◽  
Cytochrome C ◽  
Cytochrome B ◽  
Antimycin A ◽  
Alpha Band ◽  
Difference Spectra ◽  
Absorption Bands ◽  
Type C ◽  
The Difference ◽  
Mycobacterium Lepraemurium

The existence of c-type cytochrome in Mycobacterium lepraemurium was examined. The dithionite-treated cell-free extracts exhibited absorption peaks of cytochromes a + a3 and b, whereas the alpha band of c-type cytochrome at 552 nm was obscured by the large absorption peak of cytochrome b at 560 nm. The addition of NADH, NADPH, or succinate to cell-free extracts caused the reduction of b- and c-type cytochromes to nearly the same extent and thus the difference spectra displayed distinct separate peaks of b- and c-type cytochromes at 562 and 552 nm, respectively. The cell-free extracts treated with ascorbate showed absorption bands of cytochrome types c and a + a3, whereas the addition of succinate to a system preinhibited by antimycin A revealed the absorption bands of cytochrome b only. The absorption spectrum of the pyridine hemochromogens of M. lepraemurium was similar to that of mammalian cytochrome c. The results clearly indicated that, in addition to cytochromes of the a + a3 and b type, c-type cytochrome is also present in M. lepraemurium.

scholarly journals The detection and characterization by electron-paramagnetic-resonance spectroscopy of iron–sulphur proteins and other electron-transport components in chromatophores from the purple bacterium Chromatium

1974 ◽  
Vol 138 (2) ◽  
pp. 177-183 ◽  
Author(s):  
Michael C. W. Evans ◽  
Anne V. Lord ◽  
Stuart G. Reeves
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Electron Transport ◽  
Electron Acceptor ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Primary Electron ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Midpoint Potential ◽  
Primary Electron Acceptor ◽  
Electron Paramagnetic

Low-temperature e.p.r. (electron-paramagnetic-resonance) spectroscopy was used to detect electron-transport components in Chromatium chromatophores with e.p.r. signals in the g=2.00 region. High-potential iron protein (Em8.0=+325mV, where Em8.0 is the midpoint potential at pH8) and a second component (g=1.90, Em8.0=+285mV) are oxidized in illuminated chromatophores. Two iron–sulphur proteins (g=1.94) with Em8.0=−290mV and Em8.0=−50mV are present. One (Em8.0=−50mV) is reduced on illumination. A component (g=1.82) with Em8.0=−135mV is photoreduced at 10°K. The midpoint potential of this component is altered by o-phenanthroline and pH. The properties of this component suggest that it is the primary electron acceptor of a photochemical system. Another component (g=1.98) also has some of the properties of a primary electron acceptor, but its function cannot be completely defined. These results show that iron–sulphur proteins are present in the electron-transport system of Chromatium and indicate their role in electron transport.

Benzofuroxan as Electron Acceptor at Photosystem I

1987 ◽  
Vol 42 (11-12) ◽  
pp. 1265-1268
Author(s):  
B. Lotina-Hennsen ◽  
A . Garcia ◽  
M. Aguilar ◽  
M. Albores
Keyword(s):  
Electron Transport ◽  
Photosystem I ◽  
Electron Acceptor ◽  
Primary Electron ◽  
Midpoint Potential ◽  
Primary Electron Acceptor

The midpoint potential of BFO, the sensitivity of its photoreduction to DCM, DBMIB and KCN, and the photosystem I activity, suggest that the photoreduction of BFO in the chloroplast is at the primary electron acceptor x of photosystem I. and is irreversible. Rates of electron transport are similar in basal phosphorylating or uncoupled conditions al­though electron transport is coupled to photophosphorylation.

The succinate:menaquinone reductase of Bacillus cereus — characterization of the membrane-bound and purified enzyme

2008 ◽  
Vol 54 (6) ◽  
pp. 456-466 ◽  
Author(s):  
L.M. García ◽  
M.L. Contreras-Zentella ◽  
R. Jaramillo ◽  
M.C. Benito-Mercadé ◽  
G. Mendoza-Hernández ◽  
...  
Keyword(s):  
Bacillus Cereus ◽  
Cytochrome B ◽  
Kinetic Studies ◽  
Opportunistic Pathogen ◽  
Molecular Characteristics ◽  
Uptake System ◽  
Absorption Bands ◽  
Genome Database ◽  
Midpoint Potential ◽  
Maximal Absorption

Utilization of external succinate by Bacillus cereus and the properties of the purified succinate:menaquinone-7 reductase (SQR) were studied. Bacillus cereus cells showed a poor ability for the uptake of and respiratory utilization of exogenous succinate, thus suggesting that B. cereus lacks a specific succinate uptake system. Indeed, the genes coding for a succinate–fumarate transport system were missing from the genome database of B. cereus. Kinetic studies of membranes indicated that the reduction of menaquinone-7 is the rate-limiting step in succinate respiration. In accordance with its molecular characteristics, the purified SQR of B. cereus belongs to the type-B group of SQR enzymes, consisting of a 65-kDa flavoprotein (SdhA), a 29-kDa iron–sulphur protein (SdhB), and a 19-kDa subunit containing 2 b-type cytochromes (SdhC). In agreement with this, we could identify the 4 conserved histidines in the SdhC subunit predicted by the B. cereus genome database. Succinate reduced half of the cytochrome b content. Redox titrations of SQR-cytochrome b-557 detected 2 components with apparent midpoint potential values at pH 7.6 of 79 and –68 mV, respectively; the components were not spectrally distinguishable by their maximal absorption bands as those of Bacillus subtilis . The physiological properties and genome database analyses of B. cereus are consistent with the cereus group ancestor being an opportunistic pathogen.

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