Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “TITRATION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12Linked to original sources
PubMed2004

Remote titration of carvedilol for heart failure patients by advanced practice nurses.

BACKGROUND: beta-blockers (BB) in the treatment of heart failure (HF) are frequently underprescribed and underdosed, perhaps because of recommendations for office visits at each dose change. In previous work, we demonstrated the feasibility of remote telephonically assisted BB titration and found favorable effects on morbidity, time to target dose, and low withdrawal rates. In the current expanded evaluation, we reasoned that a structured remote telephonic titration protocol would achieve outcomes comparable to US Carvedilol Trials in regard to optimal dose, titration time, and morbidity. METHODS: Seventy HF patients were initiated on BB therapy (carvedilol). Before therapy, patients were instructed on BB side effects, pulse taking, and weight monitoring. Patients reported weights, vital signs, and symptoms 3 times per week by phone. Advanced practice nurses counseled, educated, and reminded patients to increase their dose every 2 weeks until target doses were reached. RESULTS: A total of 96% reached a therapeutic dose (6.25 mg twice daily). Moreover, 71% of patients reached target doses of 25 mg twice weekly in approximately 8 weeks. No HF hospitalizations occurred during remote titration. CONCLUSIONS: The use of advanced practice nurses, titration protocols, and telemanagement technologies may improve the number of HF patients initiated and treated with appropriate doses of BB.

Adrenergic beta-Antagonists↗
PubMed2005

beta-Adrenergic receptor polymorphisms and responses during titration of metoprolol controlled release/extended release in heart failure.

OBJECTIVE: beta-Blockers require careful initiation and titration when used in patients with heart failure. Some patients tolerate beta-blocker therapy initiation without difficulty, whereas in other patients this period presents clinical challenges. We tested the hypothesis that polymorphisms at codons 389 (Arg389Gly) and 49 (Ser49Gly) of the beta(1)-adrenergic receptor would be associated with differences in initial tolerability of beta-blocker therapy in patients with heart failure. We also tested whether polymorphisms in the beta(2)-adrenergic receptor, G-protein alpha s subunit (G(s)alpha), and cytochrome P450 (CYP) 2D6 genes or S-metoprolol plasma concentrations were associated with beta-blocker tolerability. METHODS: Sixty-one beta-blocker-naive patients with systolic heart failure were prospectively enrolled. Patients began taking 12.5 to 25 mg metoprolol controlled release/extended release with titration every 2 weeks (as tolerated) to 200 mg/d or the maximum tolerated dose over a period of 8 to 10 weeks. Decompensation was the composite of death, heart failure hospitalization, increase in other heart failure medications, or need to discontinue metoprolol. End points were assessed during the titration period. RESULTS: The overall rate of decompensation was not different between the codon 49 or 389 genotypes. However, a significantly greater percentage of patients with the Gly389 variant required increases in heart failure medications as compared with Arg389 homozygotes (48% versus 14%, respectively; P = .006). Similarly, patients with the Ser49 homozygous genotype were significantly more likely to require increases in concomitant heart failure therapy as compared with Gly49 carriers (41% versus 11%, respectively; P = .03). Neither CYP2D6 genotypes nor metoprolol pharmacokinetics differed between patients with and those without a decompensation event. There was no association between the beta(2)-adrenergic receptor or G(s)alpha polymorphisms with decompensated heart failure. CONCLUSIONS: Patients with the Gly389 variant and Ser49Ser genotype were significantly more likely to require increases in heart failure medications during beta-blocker titration and thus may require more frequent follow-up during titration.

Cytochrome P-450 CYP2D6↗
PubMed2004

Modeling data from titration, amide H/D exchange, and mass spectrometry to obtain protein-ligand binding constants.

We recently reported a new method for quantification of protein-ligand interaction by mass spectrometry, titration and H/D exchange (PLIMSTEX) for determining the binding stoichiometry and affinity of a wide range of protein-ligand interactions. Here we describe the method for analyzing the PLIMSTEX titration curves and evaluate the effect of various models on the precision and accuracy for determining binding constants using H/D exchange and a titration. The titration data were fitted using a 1:n protein:ligand sequential binding model, where n is the number of binding sites for the same ligand. An ordinary differential equation was used for the first time in calculating the free ligand concentration from the total ligand concentration. A nonlinear least squares regression method was applied to minimize the error between the calculated and the experimentally measured deuterium shift by varying the unknown parameters. A resampling method and second-order statistics were used to evaluate the uncertainties of the fitting parameters. The interaction of intestinal fatty-acid-binding protein (IFABP) with a fatty-acid carboxylate and that of calmodulin with Ca(2+) are used as two tests. The modeling process described here not only is a new tool for analyzing H/D exchange data acquired by ESI-MS, but also possesses novel aspects in modeling experimental titration data to determine the affinity of ligand binding.

Amides↗
PubMed2006

Effect of temperature on the acid-base properties of the alumina surface: microcalorimetry and acid-base titration experiments.

Sorption reactions on natural or synthetic materials that can attenuate the migration of pollutants in the geosphere could be affected by temperature variations. Nevertheless, most of the theoretical models describing sorption reactions are at 25 degrees C. To check these models at different temperatures, experimental data such as the enthalpies of sorption are thus required. Highly sensitive microcalorimeters can now be used to determine the heat effects accompanying the sorption of radionuclides on oxide-water interfaces, but enthalpies of sorption cannot be extracted from microcalorimetric data without a clear knowledge of the thermodynamics of protonation and deprotonation of the oxide surface. However, the values reported in the literature show large discrepancies and one must conclude that, amazingly, this fundamental problem of proton binding is not yet resolved. We have thus undertaken to measure by titration microcalorimetry the heat effects accompanying proton exchange at the alumina-water interface at 25 degrees C. Based on (i) the surface sites speciation provided by a surface complexation model (built from acid-base titrations at 25 degrees C) and (ii) results of the microcalorimetric experiments, calculations have been made to extract the enthalpic variations associated respectively to first and second deprotonation of the alumina surface. Values obtained are deltaH1 = 80+/-10 kJ mol(-1) and deltaH2 = 5+/-3 kJ mol(-1). In a second step, these enthalpy values were used to calculate the alumina surface acidity constants at 50 degrees C via the van't Hoff equation. Then a theoretical titration curve at 50 degrees C was calculated and compared to the experimental alumina surface titration curve. Good agreement between the predicted acid-base titration curve and the experimental one was observed.

Journal Article↗
PubMed2005

Titrated hypertonic/hyperoncotic solution for hypotensive fluid resuscitation during uncontrolled hemorrhagic shock in rats.

BACKGROUND: In volume- or pressure-controlled hemorrhagic shock (HS) a bolus intravenous infusion of hypertonic/hyperoncotic solution (HHS) proved beneficial compared to isotonic crystalloid solutions. During uncontrolled HS in animals, however, HHS by bolus increased blood pressure unpredictably, and increased blood loss and mortality. We hypothesized that a titrated i.v. infusion of HHS, compared to titrated lactated Ringer's solution (LR), for hypotensive fluid resuscitation during uncontrolled HS reduces fluid requirement, does not increase blood loss, and improves survival. METHODS: We used our three-phased uncontrolled HS outcome model in rats. HS phase I began with blood withdrawal of 3 ml/100g over 15 min, followed by tail amputation. Then, hydroxyethyl starch 10% in NaCl 7.2% was given i.v. to the HHS group (n=10) and LR to the control group (n=10), both titrated to prevent mean arterial pressure (MAP) from falling below 40 mmHg during HS time 20-90 min. At HS 90 min, resuscitation phase II of 180 min began with hemostasis, return of all the blood initially shed, plus fluids i.v. as needed to maintain normotension (MAP>or=70 mmHg). Liver dysoxia was monitored as increase in liver surface pCO2 during phases I and II. Observation phase III was to 72 h. RESULTS: During HS, preventing a decrease in MAP below 40 mmHg required HHS 4.9+/-0.6 ml/kg (all data mean+/-S.E.M.), compared to LR 62.2+/-16.6 ml/kg (P<0.001), with no group difference in MAP. Uncontrolled blood loss during HS from the tail stump was 13.3+/-1.9 ml/kg with HHS infusion, versus 12.6+/-2.5 ml/kg with LR infusion (P=0.73). Serum sodium concentrations were moderately elevated at the end of HS in the HHS group (149+/-3 mmol/l) versus the LR group (139+/-1 mmol/l) (P=0.001), and remained elevated throughout. Liver pCO2 increased during HS in both groups equally (P<0.001 versus baseline), and tended to return to baseline levels at the end of HS. Blood gas and lactate values throughout did not differ between groups. During HS, 2 of 10 rats in the HHS group versus 0 of 10 in the LR group died (P=0.47). There was no difference between HHS and LR groups in survival rates to 72 h (3 of 10 in the HHS group versus 2 of 10 in the LR group) (P=1.0). Survival times, by life table analysis, were not different (P=0.75). CONCLUSION: In prolonged uncontrolled HS, a titrated i.v. infusion of HHS can maintain controlled hypotension with only one-tenth of the volume of LR required, without increasing blood loss. This titrated HHS strategy may not increase the chance of long-term survival.

Animals↗
PubMed2006

Evaluation of an oral mandibular advancement titration appliance.

OBJECTIVES: To determine whether a manually adjustable oral mandibular advancement titration appliance (EMA-T) predicts successful long-term treatment with an oral mandibular advancement appliance (MAA). STUDY DESIGN: At an academic medical center, 21 adults with obstructive sleep apnea (AHI > 10 events/hr) performed baseline, titration, and MAA (Klearway) polysomnograms. During the titration polysomnogram with EMA-T, the mandible was advanced until apneas and hypopneas were eliminated or maximum tolerable advancement was reached. Participants then used the MAA at home and, once the mandible was advanced to the amount determined during the titration polysomnogram, a polysomnogram with MAA was performed. RESULTS: Mean AHI at baseline was 33.5 +/- 18.3 (SD) events/hr. During the titration polysomnogram, 9 subjects achieved an AHI < 10 and at least a 50% reduction in AHI. None of the subjects met these criteria on the MAA polysomnogram. CONCLUSIONS: EMA-T lowered the AHI to efficacious levels in 43% of patients but this acute response did not predict the efficacy of long-term MAA treatment.

Adult↗
PubMed1980

pH titrations of molluscan paramyosin at two different ionic strengths.

Paramyosin extracted from the adductor muscle of Mercenaria mercenaria, the chowder clam, was titrated both in 0.3 M KCl and in 1 mM KCl. Both the presumed native form of the molecule, acid-R-paramyosin, and a slightly degraded form, beta-paramyosin, were studied. Titrations of both types of paramyosin were similar in 1 mM k+, except that the native paramyosin is more highly charged at pH 3.2 than beta-paramyosin, as postulated previously (DeLaney and Krause, 1976, Macromolecules, 9:455), and that more groups titrate on the native molecule than on beta-paramyosin, both between pH 3.2 and 3.3 and between pH 3.2 and 10. Titrations in 0.30 M KCl, unlike those in 1 mM K, depended on starting pH; long term exposure to alkali solutions during dialysis, previously shown to cause partial dephosphorylation of paramyosin (Cooley et al., 1979, J. Biol. Chem., 254:2195), apparently also leads to a change in intermolecular interactions sufficient to cause changes in the titration curves in 0.30 M KCl but not in 1 mM K+.

Animals↗
PubMed1999

The titrations of Asp-85 and of the cation binding residues in bacteriorhodopsin are not coupled.

An outstanding problem relating to the structure and function of bacteriorhodopsin (bR), which is the only protein in the purple membrane of the photosynthetic microorganism Halobacterium salinarium, is the relation between the titration of Asp-85 and the binding/unbinding of metal cations. An extensively accepted working hypothesis has been that the two titrations are coupled, namely, protonation of Asp-85 (located in the vicinity of the retinal chromophore) and cation unbinding occur concurrently. We have carried out a series of experiments in which the purple blue equilibrium and the binding of Mn2+ ions (monitored by electron spin resonance) were followed as a function of pH for several (1-4) R = [Mn2+]/[bR] molar ratios. Data were obtained for native bR, bR mutants, artificial bR and chemically modified bR. We find that in the native pigment the two titrations are separated by more than a pKa unit [delta pKa = pKa(P/B)-pKa(Mn2+) = (4.2-2.8) = 1.4]. In the non-native systems, delta pKa values as high as 5 units, as well as negative delta pKas, are observed. We conclude that the pH titration of cation binding residues in bR is not directly related to the titration of Asp-85. This conclusion is relevant to the nature of the high affinity cation sites in bR and to their role in the photosynthetic function of the pigment.

Aspartic Acid↗
PubMed1979

Titration curves of polypeptide chains by combined isoelectric focusing-electrophoresis in 8 M urea.

Titration curves of reduced and alkylated polypeptide chains can be successfully performed in 8 M urea-polyacrylamide gel plates by electrophoresis perpendicular to a stationary stack of focused carrier ampholytes. All buffers and thiol reagents with pK values in the range pH 3--10 should be removed, since their pH-dependent ionization affects the migration and apparent pI values of the protein chains. No blurring of the patterns below pH 4.5 is observed, as usually found in titration curves in the absence of urea, thus allowing the direct titration of Glu and Asp residues. It is not possible by the present technique to titrate any group below pH ca. 3 and above pH ca. 10, due to the lack of suitable carrier ampholytes and to a "flooding" phenomenon, with concomitant identical electrophoretic mobility for all protein species, irrespective of their relative pI values and amino acid composition. The "electrophoretic titration curves" thus obtained were well correlated with the overall amino acid composition of the polypeptide chains analyzed.

Electrophoresis, Polyacrylamide Gel↗
PubMed2003

Applications and limitations of the colloid titration method for measuring activated sludge surface charges.

Surface charge quantification of polymer solutions and sludge suspensions were investigated by the colloid titration technique and compared to charge densities obtained by pH-titration. The colloid titration technique worked well for polymer samples. The charge quantity of humic acid and activated sludge extracellular polymers (EPS) was estimated to be -1.51 and -0.42 meq/g, respectively. These values are reasonable when compared to pH-titration results. The surface charge of activated sludge particles appears to be below the limit of detection. However, surface charge estimates are obtained, when the reactant doses and sample concentration are increased. It is suggested that such estimates are not correct, but artefacts of the non-stoichiometric precipitation of the polymeric reactants at high doses. It appears that the colloid titration method is limited to conditions of low reactant doses and valid for charge determination of extracted sludge polymers, whereas the method is not valid for charge determination of whole sludge.

Colloids↗
PubMed2001

A comparison of the efficacy and tolerability of titrate-to-goal regimens of simvastatin and fluvastatin: a randomized, double-blind study in adult patients at moderate to high risk for cardiovascular disease.

BACKGROUND: Use of cholesterol-lowering regimens has been shown to reduce the risk of coronary heart disease (CHD), both in primary and secondary prevention. However, there have been few studies of the relative benefits and risks of the various cholesterol-lowering agents in patient groups with specific risk factors for CHD. OBJECTIVE: The primary goal of this study was to compare the proportions of adult patients with primary hypercholesterolemia and a moderate to high risk for CHD achieving National Cholesterol Education Program low-density lipoprotein cholesterol (LDL-C) goals with titrate-to-goal regimens of simvastatin and fluvastatin. METHODS: This was a multicenter, prospective, randomized, double-blind, parallel-group study enrolling adult patients with type IIa or IIb primary hypercholesterolemia, LDL-C levels <6.0 mmol/L (<232.0 mg/dL), and triglyceride levels <4.5 mmol/L (<398.6 mg/dL), and either CHD or other atherosclerotic disease (the CHD, or high-risk, group), or multiple risk factors for CHD (the MRF, or moderate-risk, group). After a 6-week washout period, patients were randomized to 18 weeks of treatment at an initial dosage of simvastatin 10 mg once daily or fluvastatin 20 mg once daily. At 6- and 12-week titration visits, the dosage in patients who had not acheived the LDL-C goal could be increased to simvastatin 20 mg once daily and then 40 mg once daily, or to fluvastatin 40 mg once daily and then 40 mg twice daily. Lipid profiles were obtained at each titration visit and at the end of treatment. In addition to the comparison between treatments, secondary comparisons were made between the CHD and MRF subgroups within each treatment group. Statistical significance was assessed using analysis of variance. RESULTS: A total of 478 patients were enrolled, 237 in the simvastatin group and 241 in the fluvastatin group. There were no significant between-group differences in patients' characteristics at baseline. At the end of the study, 60.8% (135/222) of patients in the simvastatin group had reached target LDL-C goals, compared with 35.1% (76/216) in the fluvastatin group (P < 0.001). In the simvastatin CHD and MRF subgroups, 49% and 73%, respectively, reached the LDL-C target, compared with 19% and 50% in the corresponding fluvastatin subgroups (P < 0.001). The proportion of patients requiring titration was higher in the fluvastatin group than in the simvastatin group (87.1% and 64.1%, respectively; P = 0.001). The incidence of adverse events was similar between groups. CONCLUSION: In this study, more patients with primary hypercholesterolemia and CHD or multiple risk factors for CHD reached LDL-C goals with simvastatin treatment and required less titration than those who received fluvastatin treatment.

Adult↗
PubMed2001

Quantitative analysis of dimethyl titanocene by iodometric titration, gas chromatography and NMR.

In this study we report the use of an automated iodometric titration method and a novel gas chromatography (GC) method for the quantitative analysis of dimethyl titanocene (DMT), a key raw material in drug synthesis. Both approaches are based on the reaction of DMT in toluene or tetrahydrofuran solutions with iodine. In the case of iodometric titration, excess iodine is titrated with a standardized aqueous sodium thiosulfate solution to a potentiometric end-point for the determination of DMT concentration. Alternatively, GC is employed to measure the concentration of iodomethane, a product of the reaction between DMT and iodine, in order to determine the concentration of DMT in the solution. Excellent agreement between iodometric titration, GC and NMR results using several DMT samples confirms the accuracy of the two methods and strongly supports the use of either method as a replacement to the expensive NMR for quantitative DMT analysis. The relatively few sources of error associated with the two methods, their ubiquitous nature and ease of application in routine analysis make them the analytical methods of choice, among all. Both methods have been validated according to ICH requirements. The use of iodometric titration method for DMT analysis is demonstrated with a couple of applications.

Chromatography, Gas↗
PubMed2002

Protometric thermometric titrations of sparingly soluble compounds in water in the presence of n-octanol.

Thermometric titrimetry permits titration of acido-basic compounds in water in the presence of n-octanol. n-Octanol permits the solubilization of protolytes and moreover may also displace the equilibria of the titration reactions. Hydrochlorides of highly insoluble derivatives such as phenothiazine derivatives can be titrated with satisfactory accuracy and precision by sodium hydroxide despite their high pK(a) values. Likewise barbiturate salts can be titrated by hydrochloric acid. In the case of some salts, the methodology may permit the sequential titration of the ion and counter ion.

1-Octanol↗
PubMed1997

Etomidate and thiopental-based anesthetic induction: comparisons between different titrated levels of electrophysiologic cortical depression and response to laryngoscopy.

STUDY OBJECTIVE: To determine whether etomidate-based induction can provide better hemodynamics than a standard thiopental sodium-based anesthetic induction. DESIGN: Prospective, single-blind clinical trial. SETTING: Multicenter university neurosurgical operating room. PATIENTS: 66 ASA physical status II and III inpatients undergoing neurosurgical procedures for intracranial tumor or other pathology. INTERVENTIONS: Patients were divided into two groups for anesthetic induction. The first group (control) was divided into two subgroups, with the first subgroup receiving "low-dose" etomidate (LET) 0.4 to 0.6 mg/kg titrated to an electroencephalographic (EEG) spectral edge frequency (SEF) of 10 to 12 Hz. The second subgroup received thiopental sodium (THIO) 3 to 6 mg/kg titrated to the same EEG endpoint. The study group was given high-dose etomidate (HET) 0.5 to 1.7 mg/kg titrated to an early burst suppression pattern. MEASUREMENTS AND MAIN RESULTS: Baseline (awake) measurements of mean arterial pressure (MAP) heart rate (HR), and SEF were obtained prior to anesthetic induction that was accomplished using a small bolus plus an infusion of the induction drug titrated to the EEG target. MAP, HR, and SEF were recorded just prior to laryngoscopy and intubation (T1), 30 seconds after laryngoscopy and intubation (T2), and 90 seconds after (T3) laryngoscopy and intubation. Times to reach EEG endpoint, along with total dose of anesthetic given, were also recorded. Compared with baseline values, the THIO group had the highest increase in both HR (22.9 +/- 4.4 bpm.) and MAP (16.8 +/- 4.2 mmHg) (P < 0.05) after laryngoscopy and intubation. The LET group also had significant increases compared with the HET group that demonstrated the least hemodynamic variability. No correlations could be made between age and dose of induction drug. CONCLUSIONS: Etomidate-based anesthetic induction, titrated to EEG burst suppression, produced stable hemodynamics during laryngoscopy and intubation as compared with lower dose, more "classic" inductions with etomidate or thiopental.

Adult↗
PubMed2000

Spectrophotometric titration of ionisable groups in proteins: a theoretical study.

A simple theoretical model is proposed for evaluation of the optical titration behaviour of tyrosyl and carboxyl residues in proteins. The pK values involved in the model are computed using the semi-empirical method. The titration curves are calculated using the values of the molar absorption differences for tyrosyl residues in the ultraviolet (UV) region at 245 and 295 nm, and for carboxyl residues in the infrared (IR) region at 1565 and 1707 cm(-1), respectively. The theoretical tyrosyl titration curves are compared with the experimental data for lysozyme, myoglobin and chymotrypsinogen (available in the literature). This approach provides a good tool for distinguishing between the ionisation and the conformational changes in the alkaline range. The quantitative evaluation of the change of molar extinction coefficients as a function of pH in the case of carboxyl titration for lysozyme, trypsin and cytochrome c shows a good agreement with the experimental titration data.

Cytochrome c Group↗
PubMed2005

Determination of metal speciation by reverse titrations.

A new method is proposed to determine metal speciation by varying the concentration of a competing ligand at a constant metal concentration, with detection by cathodic stripping voltammetry. The free metal ion concentration is gradually lowered from its natural level while the method probes progressively deeper into the already complexed metal fraction: it is therefore a reverse titration rather than the forward titration which is used for conventional complexing ligand titrations. The sensitivity is greatest at the lowest free metal ion concentration, where it matters most, and the method can be carried out in a single sample aliquot in the voltammetric cell. The method is applied here to copper speciation, but in principle, it can also be used for other metals. Modeling shows that this method has good sensitivity at ligand concentrations near the metal concentration (lower as well as greater). Comparative measurements of copper speciation using reverse and forward titrations of representative water samples of oceanic and coastal origin show good agreement. The data showed that these samples did not contain low levels of strong ligands in addition to the ligands detected by the forward titrations.

Journal Article↗
PubMed1992

Relationship between electrostatics and redox function in human thioredoxin: characterization of pH titration shifts using two-dimensional homo- and heteronuclear NMR.

The electrostatic behavior of potentially titrating groups in reduced human thioredoxin was investigated using two-dimensional (2D) 1H and 15N nuclear magnetic resonance (NMR) spectroscopy. A total of 241 chemical shift titration curves were measured over the pH range of 2.1-10.6 from homonuclear 1H-1H Hartmann-Hahn (HOHAHA) and heteronuclear 1H-15N Overbodenhausen correlation spectra. Nonlinear least-squares fits of the data to simple relationships derived from the Henderson-Hasselbalch equation led to the determination of pKas for certain isolated ionizable groups, including the single histidine residue at position 43 (pKa = 5.5 +/- 0.1) and a number of aspartic and glutamic acid carboxylate groups. Many of the titration curves demonstrate complex behavior due to the effects of interacting titrating groups, the long range of electrostatic interactions through the protein interior, and, perhaps, pH-induced conformational changes on the chemical shifts. Unambiguous assignment of the pKas for most of the 38 potentially ionizing groups of human thioredoxin could therefore not be made. In addition, there was no clear evidence that Asp-26 titrates in a manner corresponding to that observed in the Escherichia coli protein [Dyson, H. J., Tennant, L. L., & Holmgren, A. (1991) Biochemistry 30, 4262-4268]. The pKas of the active site cysteines were measured, however, with Cys-32 having an anomalously low value of 6.3 +/- 0.1 and that of Cys-35 between 7.5 and 8.6. These pKas are in agreement with proposed mechanisms for redox catalysis of thioredoxin and previously measured pKas within the active site of E. coli thioredoxin [Kallis, G. B., & Holmgren, A. (1980) J. Biol. Chem. 255, 10261-10265]. The stabilization of a thiolate anion at physiological pH can be explained by the interaction of the S gamma of Cys-32 with the amide of Cys-35 observed in the previously determined high-resolution solution structure of reduced human thioredoxin [Forman-Kay, J. D., Clore, G. M., Wingfield, P. T., & Gronenborn, A. M. (1991) Biochemistry 30, 2685-2698].

Binding Sites↗
PubMed1992

Redox titrations of carbon monoxide dehydrogenase from Clostridium thermoaceticum.

Redox titrations of carbon monoxide dehydrogenase (CODH) from Clostridium thermoaceticum were performed using the reductant CO and the oxidant thionin. Titrations were followed at 420 nm, a wavelength sensitive to redox changes of the iron-sulfur clusters in the enzyme. When CODH was oxidized by just enough thionin to maximize A420, two molecules of CO per mole of CODH dimer (4 equiv/mol) reduced the enzyme fully. Likewise, 4 equiv/mol of thionin oxidized the fully-reduced enzyme to the point where A420 maximized. The four n = 1 redox sites which titrated in this region were designated group I sites. They include at least two iron-sulfur clusters, [Fe/S]A and [Fe/S]B, and two other sites, A' and B'. The [Fe4S4]2+/1+ cluster in CODH is included in this group. [Fe/S]B and B' have reduction potentials (at pH 8) below -480 mV vs NHE; [Fe/S]A and A' have reduction potentials above that value. The reduction potential of either [Fe/S]B or B' is near to the CO/CO2 couple at pH 8 (-622 mV). When CODH was oxidized by more than enough thionin to maximize A420, some of the excess thionin oxidized the so-called group II redox sites. These sites have reduction potentials more positive than group I and do not exhibit changes at 420 nm when titrated. Titration of group II sites required 1-2 equiv/mol. EPR of reduced group II sites exhibited the gav = 1.82 signal. When these sites were oxidized, the only signal present had g values at 2.075, 2.036, and 1.983.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldehyde Oxidoreductases↗