Quantifying Pseudomonas aeruginosa adhesion to contact lenses

PURPOSE

Pseudomonal keratitis can occur in soft contact lens wearers following compromise of the corneal epithelium and exposure to pathogens. This study was initiated to determine if Pseudomonas aeruginosa has the ability to adhere preferentially to unused contact lenses made from different FDA group polymers.

METHODS

Pseudomonas aeruginosa (strain PA01) was grown to its early stationary phase and diluted into phosphate-buffered saline to a concentration of 12000 to 16000 cells/mL. Samples from each of the four FDA-designated polymer classes used for the manufacture of soft lenses were incubated in pseudomonal inoculant for 4 hours. The lenses were removed and the number of bacteria bound was quantified using electrical impedance particle counting.

RESULTS

A lens constructed from a group I polymer (nonionic polymer with <50% water) bound the fewest bacteria (7.2% of total cells +/- 1.0 SD) whereas a lens made from group II polymers (nonionic polymer with >50% water) showed the highest level of bacterial binding (42% of total cells +/- 4.5 SD). Lenses constructed from group III and IV polymers showed intermediate levels of bacterial binding (28.4% +/- 1.8 SD and 29.3% +/- 1.7 SD, respectively).

CONCLUSIONS

The polymer type used to construct the contact lens may influence subsequent bacterial adhesion events. Contact lenses made from nonionic polymers with high water content may carry higher risks of bacterial contamination.

Allosteric binding properties of a monoclonal antibody and its Fab fragment

Detailed equilibrium binding studies were conducted on a monoclonal antibody directed against Pb(II) complexed with a protein conjugate of diethylenetriaminepentaacetic acid (DTPA). Binding curves obtained with DTPA and a cyclohexyl derivative of DTPA in the presence and absence of metal ions were consistent with the anticipated one-site homogeneous binding model. Binding curves obtained with aminobenzyl-DTPA or its complexes with Ca(II), Sr(II), and Ba(II) were highly sigmoidal, characterized by Hill coefficients of 2.3-6.5. Binding curves obtained with the Pb(II) and In(III) complexes of aminobenzyl-DTPA were hyperbolic, but in each case the apparent affinity of the antibody for the chelator-metal complex was higher in the presence of excess chelator than it was in the presence of excess metal ion. In the presence of excess chelator, the equilibrium dissociation constant for the binding of aminobenzyl-DTPA-Pb(II) to the antibody was 9.5 x 10(-)(10) M. Binding curves obtained with the Hg(II) and Cd(II) complexes of aminobenzyl-DTPA were biphasic, indicative of negative cooperativity. Further binding studies demonstrated that aminobenzyl-DTPA-Hg(II) opposed the binding of additional chelator-metal complexes to the antibody more strongly than did aminobenzyl-DTPA-Cd(II). The Fab fragment differed from the intact antibody only in that the apparent affinity of the Fab was generally lower for a given chelator-metal complex. These data are interpreted in terms of a model in which (i) aminobenzyl-DTPA and its complexes bind both to the antigen binding site and to multiple charged sites on the surface of the compact immunoglobulin; and (ii) the bound, highly charged ligands interact in a complicated fashion through the apolar core of the folded antibody.

Kinetic rate constant for electron transfer between ferrous ions and novel Rusticyanin isoform in Acidithiobacillus ferrooxidans

Here we report the kinetic rate constant for electron transfer from ferrous ions to a novel rusticyanin isoform in Acidithiobacillus ferrooxidans. The second order rate constant for this isoform is shown to be approximately one half that of the previously known type, 0.09 M(-1)s(-1) vs. 0.14 M(-1)s(-1).

Near real-time biosensor-based detection of 2,4-dinitrophenol

A fluorescent biosensor assay has been developed for near real-time detection of 2,4-dinitrophenol (DNP). The assay was based on fluorescent detection principles that allow for the analysis of antibody/antigen interactions in solution using the KinExA immunoassay instrument. Our KinExA consisted of a capillary flow observation cell containing a microporous screen that maintains a compact capture antigen-coated bead bed. The bead bed was comprised of polymethylmethacrylate (PMMA) beads coated with dinitrophenol-human serum albumin (DNP-HSA) conjugate. Phosphate buffered saline (PBS) solutions, containing various concentrations of free DNP, were incubated for 30 min with mouse anti-DNP monoclonal antibody to equilibrium. Solutions containing the DNP-monoclonal antibody complex and possible excess free antibodies were then passed over DNP-HSA labeled beads. The free monoclonal anti-DNP antibody, if available, was then bound to the DNP-HSA fixed on the beads. The system was then flushed with excess PBS to remove unbound reactants in the bead bed. The beads were then subjected to brief contact with PBS solutions containing goat anti-mouse fluorescein isothiocyanate (FITC)-labeled secondary antibody, once again, followed by a short PBS flush. The fluorescence was recorded during the addition of the FITC labeled secondary antibody to the bead bed through the final PBS flushing with the KinExA. The amount of DNP detected could then be determined from the fluorescent slopes that were generated or by the remaining fluorescence that was retained on the beads after final PBS flushing of the system. This assay has been able to detect a minimum of 5 ng/ml of DNP in solution and can be adapted for other analytes of interest simply by changing the capture antigen and antibody pairs.

Antibody-based sensors for heavy metal ions

Competitive immunoassays for Cd(II), Co(II), Pb(II) and U(VI) were developed using identical reagents in two different assay formats, a competitive microwell format and an immunosensor format with the KinExA 3000. Four different monoclonal antibodies specific for complexes of EDTA-Cd(II), DTPA-Co(II), 2,9-dicarboxyl-1,10-phenanthroline-U(VI), or cyclohexyl-DTPA-Pb(II) were incubated with the appropriate soluble metal-chelate complex. In the microwell assay format, the immobilized version of the metal-chelate complex was present simultaneously in the assay mixture. In the KinExA format, the antibody was allowed to pre-equilibrate with the soluble metal-chelate complex, then the incubation mixture was rapidly passed through a microcolumn containing the immobilized metal-chelate complex. In all four assays, the KinExA format yielded an assay with 10-1000-fold greater sensitivity. The enhanced sensitivity of the KinExA format is most likely due to the differences in the affinity of the monoclonal antibodies for the soluble versus the immobilized metal-chelate complex. The KinExA 3000 instrument and the Cd(II)-specific antibody were used to construct a prototype assay that could correctly assess the concentration of cadmium spiked into a groundwater sample. Mean analytical recovery of added Cd(II) was 114.25+/-11.37%. The precision of the assay was satisfactory; coefficients of variation were 0.81-7.77% and 3.62-14.16% for within run and between run precision, respectively.

Binding properties of a monoclonal antibody directed toward lead-chelate complexes

A monoclonal antibody (2C12) that recognizes a Pb(II)-cyclohexyldiethylenetriamine pentaacetic acid complex was produced by the injection of BALB/c mice with a Pb(II)-chelate complex covalently coupled to a carrier protein. The ability of purified antibody to interact with a variety of metal-free chelators and metal-chelate complexes was assessed by measuring equilibrium dissociation constants. The antibody bound to metal-free trans-cyclohexyldiethylenetriamine pentaacetic acid (CHXDTPA) with an equilibrium dissociation constant of 2.3 x 10(-)(7) M. Addition of Pb(II) increased the affinity of the antibody for the complex by 25-fold; Pb(II) was the only metal cation (of 15 different di-, tri-, and hexavalent metals tested) that increased the affinity of the antibody for CHXDTPA. The increased affinity was due primarily to an increase in the association rate constant. The antibody also had the ability to interact with ethylenediamine tetraacetic acid (EDTA), diethylenetriamine pentaacetic acid (DTPA), and structurally related derivatives, but with affinities from 50- to 10000-fold less than that determined for CHXDTPA. Addition of metals to EDTA-based chelators reduced the affinity of the antibody for these ligands. However, when DTPA was used as the chelator, addition of Pb(II) increased the affinity of the antibody for the complex by 200-fold. The sensitivity of prototype immunoassays for Pb(II) could be modulated by changing the structure of the immobilized metal-chelate complex and/or the soluble chelator used to complex Pb(II) in the test solution.

Automated kinetic exclusion assays to quantify protein binding interactions in homogeneous solution

A method was developed for the quantification of protein-ligand interactions in which the free protein present in homogeneous reaction mixtures was separated and quantified using a KinExA immunoassay instrument. Separation was achieved by rapid percolation of the reaction mixture over a column of microbeads whose surfaces were coated with an immobilized form of the ligand. The protein thus captured was quantified using a fluorescently labeled anti-protein antibody. The features of this new method were illustrated using a model system in which each of the principal reagents was covalently labeled with a different fluorescent molecule: mouse monoclonal anti-biotin primary antibody (fluorescein), biotin (B-phycoerythrin), and goat anti-mouse polyclonal secondary antibody (indodicarbocyanin). Values for the equilibrium and kinetic rate constants for the binding between the anti-biotin antibody and biotin conjugated with B-phycoerythrin were determined and shown to be independent of whether the fluorescent label was located on the primary or secondary antibody. Equilibrium binding experiments conducted with (F(AB))(2) and corresponding F(AB) fragments showed that the valency of the binding protein had no influence on the value of the dissociation constant. The values of the equilibrium and rate constants obtained by this new method are those for the binding reaction in homogeneous solution; the immobilized ligand is only a tool exploited for the separation and quantification of the free protein.

Solid-phase synthesis and characterization of carcinoembryonic antigen (CEA) domains

Carcinoembryonic antigen (CEA), a 180,000 dalton cell surface glycoprotein expressed on tumors of the colon, breast, ovary, and lung, has seven predicted immunoglobulin-like domains (N-A1-B1-A2-B2-A3-B3), most of which are recognized by distinct monoclonal antibodies. To study the individual domains, we have prepared several of the domains (N, A3, B3, and A3-B3) by solid-phase peptide synthesis. The syntheses were performed by the Fmoc method using single couplings, elevated temperatures for both the coupling and deblocking reactions, and a flexible solvent system for the coupling reactions. The syntheses were accomplished on an in-house built synthesizer which allowed for temperature control and flexible solvent control during the course of the coupling reactions. Due to the large size of the peptides (84-184 residues), it was anticipated that the overall purity of the final product would not exceed 60% even for an average coupling yield of 99.5%. Therefore, several of the peptides were synthesized with a His6 "tail" at the amino terminus, allowing for purification on a Ni-NTA chelate column. For the most part, the purified peptides exhibited single sharp peaks by RP-HPLC, migrated at their expected molecular weights by gel permeation chromatography, gave correct masses by electrospray ionization or matrix-assisted laser desorption ionization time of flight mass spectrometry, gave the expected amino acid analyses, N-terminal sequences, and tryptic maps, and bound their appropriate monoclonal antibodies. The N-domain was extremely hydrophobic, requiring 6M guanidinium hydrochloride for solubilization, the A3 domain was soluble in dilute acid, and the B3 domain had an intermediate solubility. The affinity constants of the A3 domain and several mutants (also made by peptide synthesis) are reported, along with characterization of the 178 amino acid two-domain peptide, A3-B3. Although there is no evidence for proper folding of these domains by NMR, their ability to bind monoclonal antibodies with high affinity suggests that this is a plausible approach for producing individual domains of CEA.

Multiple wavelength anomalous diffraction (MAD) crystal structure of rusticyanin: a highly oxidizing cupredoxin with extreme acid stability

The X-ray crystal structure of the oxidized form of the extremely stable and highly oxidizing cupredoxin rusticyanin from Thiobacillus ferrooxidans has been determined by the method of multiwavelength anomalous diffraction (MAD) and refined to 1.9 A resolution. Like other cupredoxins, rusticyanin is a copper-containing metalloprotein, which is composed of a core beta-sandwich fold. In rusticyanin the beta-sandwich is composed of a six- and a seven-stranded beta-sheet. Also like other cupredoxins, the copper ion is coordinated by a cluster of four conserved residues (His85, Cys138, His143, Met148) arranged in a distorted tetrahedron. Rusticyanin has a redox potential of 680 mV, roughly twice that of any other cupredoxin, and it is optimally active at pH values < or = 2. By comparison with other cupredoxins, the three-dimensional structure of rusticyanin reveals several possible sources of the chemical differences, including more ordered secondary structure and more intersheet connectivity than other cupredoxins. The acid stability and redox potential of rusticyanin may also be enhanced over other cupredoxins by a more extensive internal hydrogen bonding network and by more extensive hydrophobic interactions surrounding the copper binding site. Finally, reduction in the number of charged residues surrounding the active site may also make a major contribution to acid stability. We propose that the resulting rigid copper binding site, which is constrained by the surrounding hydrophobic environment, structurally and electronically favours Cu(I). We propose that the two extreme chemical properties of rusticyanin are interrelated; the same unique structural features that enhance acid stability also lead to elevated redox potential.

NMR solution structure of Cu(I) rusticyanin from Thiobacillus ferrooxidans: structural basis for the extreme acid stability and redox potential

The solution structure of the Cu(I) form of the rusticyanin from Thiobacillus ferrooxidans has been calculated from a total of 1979 distance and dihedral angle constraints derived from 1H, 13C and 15N NMR spectra. The structures reveal two beta-sheets, one of six strands and one of seven strands that are tightly packed in a beta-barrel or beta-sandwich arrangement, and a short helix that extends on the outside of one of the sheets to form a second hydrophobic core. The copper coordination sphere is composed of the standard type I ligands (His2CysMet) in a distorted tetrahedral arrangement. The copper-binding site is located within a hydrophobic region at one end of the molecule, surrounded by a number of aromatic rings and hydrophobic residues. This configuration probably contributes to the acid stability of the copper site, since close association of the aromatic rings with the histidine ligands would sterically hinder their dissociation from the copper. An electrostatic analysis based on a comparison of the structures of rusticyanin and French bean plastocyanin shows that factors determining the high redox potential of rusticyanin include contributions from charged side-chains and from the disposition of backbone peptide dipoles, particularly in the 81 to 86 region of the sequence and the ligand cysteine residue. These interactions should also contribute to the acid stability by inhibiting protonation of His143.

Metal binding properties of a monoclonal antibody directed toward metal-chelate complexes

A monoclonal antibody that recognizes cadmium-EDTA complexes has been produced by the injection of BALB/c mice with a metal-chelate complex covalently coupled to a carrier protein. The ability of purified antibody to recognize 16 different metal-EDTA complexes was assessed by measuring equilibrium binding constants using a KinExATM immunoassay instrument. The antibody bound to cadmium- and mercury-EDTA complexes with equilibrium dissociation constants of 21 and 26 nM, respectively. All other metal-EDTA complexes tested, including those of Mn(II), In(III), Ni(II), Zn(II), Co(II), Cu(II), Ag(I), Fe(III), Pb(II), Au(III), Tb(III), Ga(III), Mg(II), and Al(III) bound with affinities from 20- to 40,000-fold less than that determined for the cadmium-EDTA complex. With the exception of mercury and magnesium, the binding of divalent metal-chelate complexes was well-correlated with the size of the metal ion. The amino acid sequences of the heavy and light chain variable regions were deduced from polymerase chain reaction-amplified regions of the corresponding genes and subsequently used to construct molecular models of the antigen binding region. The key residue for cadmium binding in the model for 2A81G5 appeared to be histidine 96 in the heavy chain.

Gene synthesis, high-level expression, and mutagenesis of Thiobacillus ferrooxidans rusticyanin: His 85 is a ligand to the blue copper center

An artificial gene of the blue copper protein rusticyanin from Thiobacillus ferrooxidans was constructed from eight overlapping oligonucleotides in a recursive "one-pot" polymerase chain reaction. The gene was placed behind the T7/lacOR promoter of pET24a and expressed in Escherichia coli as a soluble protein. A purification scheme involving a pH titration step, cation-exchange chromatography, and reverse-phase HPLC separation provided yields of the apoprotein ranging from 70 to 100 mg/L of cell culture; reconstitution with Cu(II) is quantitative at pH 3.4-5.5. The redox reactions and the electronic absorption and EPR spectra of the recombinant Cu(II)-rusticyanin and NMR spectra of the reduced holoprotein are indistinguishable from those of the protein derived from T. ferrooxidans. Rusticyanin possesses the phylogenetically conserved carboxy-terminal loop of three copper ligands (Cys 138, His 143, and Met 148), but the identity of the fourth ligand was not clear from sequence homology to other blue copper proteins. To address this question directly, we have prepared two site-specific mutants where two of the proposed ligands, Asp 73 and His 85, have been replaced with alanine. The Asp73Ala mutant retained the electronic properties of the wild-type blue copper center (absorption maxima at 452, 597, and 750 nm), whereas the His85Ala variant gave rise to a green type 1 copper protein (absorption maxima at 455 and 618 nm).(ABSTRACT TRUNCATED AT 250 WORDS)

Nuclear magnetic resonance 15N and 1H resonance assignments and global fold of rusticyanin. Insights into the ligation and acid stability of the blue copper site

Nuclear magnetic resonance assignments are reported at pH approximately 3 for a type 1 ("blue") copper protein, rusticyanin, obtained from the acidophilic organism Thiobacillus ferrooxidans. A combination of homonuclear proton and heteronuclear 15N-edited NMR spectra has been used to assign most of the 1H and 15N resonances of reduced rusticyanin. The copper-binding site is shown by analogy with other blue copper proteins to contain the side-chains of Cys138, His143 and Met148 at the C-terminal end of the sequence and a fourth ligand that is most likely a histidine, His85, consistent with the constitution of other type 1 copper sites. The global fold of the molecule is a compact beta-barrel or beta-sandwich, which contains a high proportion of beta-sheet secondary structure and a hydrophobic core particularly rich in aromatic residues. The copper-binding active site is surrounded by aromatic residues, and many of the resonances of the residues flanking the active site are shifted to unusual values, consistent with the effects of ring currents. The protected nature of the copper site is demonstrated by the large number of amide protons that are persistent in this region in 99% 2H2O solution at pH 3.4. We suggest that the unusual acid stability, both of the protein itself and of the blue copper active site, is a direct result of the protected and highly hydrophobic nature of the active site sequence and contacting loops and the high proportion of secondary structure in the protein.

Solubilization of Minerals by Bacteria: Electrophoretic Mobility of Thiobacillus ferrooxidans in the Presence of Iron, Pyrite, and Sulfur

Thiobacillus ferroxidans is an obligate acidophile that respires aerobically on pyrite, elemental sulfur, or soluble ferrous ions. The electrophoretic mobility of the bacterium was determined by laser Doppler velocimetry under physiological conditions. When grown on pyrite or ferrous ions, washed cells were negatively charged at pH 2.0. The density of the negative charge depended on whether the conjugate base was sulfate, perchlorate, chloride, or nitrate. The addition of ferric ions shifted the net charge on the surface asymptotically to a positive value. When grown on elemental sulfur, washed cells were close to their isoelectric point at pH 2.0. Both pyrite and colloidal sulfur were negatively charged under the same conditions. The electrical double layer around the bacterial cells under physiological conditions exerted minimal electrostatic repulsion in possible interactions between the cell and either of its charged insoluble substrates. When Thiobacillus ferrooxidans was mixed with either pyrite or colloidal sulfur at pH 2.0, the mobility spectra of the free components disappeared with time to be replaced with a new colloidal particle whose electrophoretic properties were intermediate between those of the starting components. This new particle had the charge and size properties anticipated for a complex between the bacterium and its insoluble substrates. The utility of such measurements for the study of the interactions of chemolithotrophic bacteria with their insoluble substrates is discussed.

Respiratory enzymes of Thiobacillus ferrooxidans. Kinetic properties of an acid-stable iron:rusticyanin oxidoreductase

Rusticyanin is an acid-stable, soluble blue copper protein found in abundance in the periplasmic space of Thiobacillus ferrooxidans, an acidophilic bacterium capable of growing autotrophically on soluble ferrous sulfate. An acid-stable iron:rusticyanin oxidoreductase activity was partially purified from cell-free extracts of T. ferrooxidans. The enzyme-catalyzed, iron-dependent reduction of the rusticyanin exhibited three kinetic properties characteristic of aerobic iron oxidation by whole cells. (i) A survey of 14 different anions indicated that catalysis by the oxidoreductase occurred only in the presence of sulfate or selenate, an anion specificity identical to that of whole cells. (ii) Saturation with both sulfatoiron(II) and the catalyst produced a concentration-independent rate constant of 3 s-1 for the reduction of the rusticyanin, which is an electron transfer reaction sufficiently rapid to account for the flux of electrons through the iron respiratory chain. (iii) Values for the enzyme-catalyzed pseudo-first-order rate constants for the reduction of the rusticyanin showed a hyperbolic dependence on the concentration of sulfatoiron(II) with a half-maximal effect at 300 microM, a value similar to the apparent KM for iron shown by whole cells. On the basis of these favorable comparisons between the behavior patterns of isolated biomolecules and those of whole cells, this iron:rusticyanin oxidoreductase is postulated to be the primary cellular oxidant of ferrous ions in the iron respiratory electron transport chain of T. ferrooxidans.

Enzyme immunoassay to determine heavy metals using antibodies to specific metal-EDTA complexes: optimization and validation of an immunoassay for soluble indium

An immunoassay that measures soluble indium at concentrations from 0.005 ppb to 320 ppm is described. The assay utilized a monoclonal antibody that binds specifically to indium-EDTA complexes in an antigen-inhibition format. The sensitivity of the assay could be modulated by changing the nature of the soluble inhibiting antigen. The range of the assay was from 0.6 to 320 ppm, 0.1 to 120 ppm, or 0.005 to 2000 ppb when indium-EDTA, indium-(p-nitrobenzyl)-EDTA, or indium-EDTA-bovine serum albumin, respectively was used as the soluble inhibiting antigen. The assay reliably monitored indium concentration in the presence of a 100-fold excess of manganese, magnesium, or copper ions and the quantitation of indium by immunoassay correlated closely with the values obtained using atomic absorption spectroscopy. This technology could be employed in immunoassays for other metals that are priority pollutants.

Sensitivity of Iron-Oxidizing Bacteria, Thiobacillus ferrooxidans and Leptospirillum ferrooxidans , to Bisulfite Ion

When grown on iron-salt medium supplemented with the bisulfite ion, Leptospirillum ferrooxidans was much more sensitive to the ion than was Thiobacillus ferrooxidans . The causes of the sensitivity of L. ferrooxidans to the bisulfite ion were studied. The bisulfite ion completely inhibited the iron-oxidizing activities of L. ferrooxidans and T. ferrooxidans at 0.02 and 0.2 mM, respectively. A trapping reagent for the bisulfite ion, formaldehyde, completely reversed the inhibition. The treatment of intact cells with 1.0 mM bisulfite ion for 1 h and washing the bisulfite ion from the cells had no harmful effects on the iron-oxidizing activity of T. ferrooxidans . However, the treatment of L. ferrooxidans with 0.1 mM bisulfite ion for 1 h completely destroyed the iron-oxidizing activity. T. ferrooxidans had sulfite:ferric ion oxidoreductase activity. In contrast, a quite low level of sulfite:ferric ion oxidoreductase activity was found in L. ferrooxidans , suggesting that it is much more difficult for L. ferrooxidans to oxidize the bisulfite ion to the less harmful sulfate than it is for T. ferrooxidans . These results suggest that the sensitivity of L. ferrooxidans to the bisulfite ion is due to a lack of an active sulfite:ferric ion oxidoreductase and the sensitivity of its iron oxidase to bisulfite ion.

Enzymes of aerobic respiration on iron

Bacteria capable of aerobic respiration on ferrous ions are spread throughout eubacterial and archaebacterial phyla. Comparative spectroscopic analyses revealed that phylogenetically distinct organisms expressed copious quantities of spectrally distinct redox-active biomolecules during autotrophic growth on soluble iron. Thiobacillus ferroxidans, Leptospirillum ferrooxidans, Sulfobacillus thermosulfidooxidans, and Metallosphaera sedula possessed iron respiratory chains dominated by a blue copper protein, a novel red cytochrome, a novel yellow protein, and a novel yellow cytochrome, respectively. Further investigation of each type of respiratory chain will be necessary to deduce the advantages and disadvantages of each.

Crystallization and preliminary X-ray crystallographic studies of rusticyanin from Thiobacillus ferrooxidans

Rusticyanin is a 16.5 kDa type I blue copper protein isolated from Thiobacillus ferrooxidans. This organism can grow on Fe2+ as its sole energy source. Rusticyanin is thought to be a principal component in the iron respiratory electron transport chain of T. ferrooxidans. As a component of the periplasmic space of an acidophilic bacterium, rusticyanin is remarkably stable at acidic pH. It is redox-active down to pH 0.2. Crystals of rusticyanin have been grown from solutions of PEG 8000 by the hanging-drop vapor diffusion method. The crystals are orthorhombic, space group P2(1)2(1)2(1), with unit cell dimensions a = 32.36 A, b = 60.37 A, c = 74.60 A. The crystals diffract to 2.0 A resolution and they are stable in the X-ray beam for at least two days.

Existence of a Hydrogen Sulfide:Ferric Ion Oxidoreductase in Iron-Oxidizing Bacteria

The existence of a hydrogen sulfide:ferric ion oxidoreductase, which catalyzes the oxidation of elemental sulfur with ferric ions as an electron acceptor to produce ferrous and sulfite ions, was assayed with washed intact cells and cell extracts of various kinds of iron-oxidizing bacteria, such as Thiobacillus ferrooxidans 13598, 13661, 14119, 19859, 21834, 23270, and 33020 from the American Type Culture Collection, Leptospirillum ferrooxidans 2705 and 2391 from the Deutsche Sammlung von Mikroorganismen, L. ferrooxidans BKM-6-1339 and P3A, and moderately thermophilic iron-oxidizing bacterial strains BC1, TH3, and Alv. It was found that hydrogen sulfide:ferric ion oxidoreductase activity comparable to that of T. ferrooxidans AP19-3 was present in all iron-oxidizing bacteria tested, suggesting a wide distribution of this enzyme in iron-oxidizing bacteria.

Amino acid sequence of the blue copper protein rusticyanin from Thiobacillus ferrooxidans

Rusticyanin is a small blue copper protein isolated from Thiobacillus ferrooxidans. The amino acid sequence of the rusticyanin has been determined by the structural characterization of tryptic and endoproteinase Asp-N peptides with use of amino terminal microsequencing, fast atom bombardment mass spectrometry, and electrospray triple-quadrupole mass spectrometry techniques. Amino acid analysis, carboxy-terminal sequence analysis, and circular dichroism spectroscopy were also performed on the protein. Amino acid sequence identity among rusticyanin and six other small blue copper proteins is apparent only in the limited C-terminal region of each protein bearing three of the four putative copper ligands. A structural model of the rusticyanin is proposed where the protein is principally a beta-barrel comprised of six strands. This model is consistent with the circular dichroism data and computational predictions of the secondary structure of rusticyanin. A feature of the model is the hypothesis that Asp 73 may serve as a fourth copper ligand.

Effect of divers anions on the electron-transfer reaction between iron and rusticyanin from Thiobacillus ferrooxidans

Rusticyanin is a soluble blue copper protein found in abundance in the periplasmic space of Thiobacillus ferrooxidans, an acidophilic bacterium capable of growing chemolithotrophically on soluble ferrous sulfate. The one-electron-transfer reactions between soluble iron and purified rusticyanin were studied by stopped-flow spectrophotometry in acidic solutions containing each of 14 different anions. The second-order rate constants for both the Fe(II)-dependent reduction and the Fe(III)-dependent oxidation of the rusticyanin varied as a function of the identity of the principal anion in solution. Analogous electron-transfer reactions between soluble iron and bis(dipicolinato)cobaltate(III) or bis(dipicolinato)ferrate(II) were studied by stopped-flow spectrophotometry under solution conditions identical with those of the rusticyanin experiments. Similar anion-dependent reactivity patterns were obtained with soluble iron whether the other reaction partner was rusticyanin or either of the two organometallic complexes. The Marcus theory of outer-sphere electron transfer reactions was applied to this set of kinetic data to demonstrate that the rusticyanin may possess at least two electron-transfer pathways for liganded iron, one where the pattern of electron-transfer reactivity is controlled largely by protein-independent activation parameters and one where the protein exhibits an anion-dependent kinetic specificity. The exact role of rusticyanin in the iron-dependent respiratory electron transport chain of T. ferrooxidans remains unclear.