Optimization of the radiosynthesis of [68Ga]Ga-PSMA-11 using a Trasis MiniAiO synthesizer: do we need to heat and purify?

INTRODUTION:: [Ga]Ga-prostate specific membrane antigen (PSMA)-11 showed a clear gain in sensitivity for lesion detection in the biological recurrence of prostate cancer as compared to the standard [F]fluorocholine radiopharmaceutical. To meet the strong demand for [Ga]Ga-PSMA-11, we aimed to optimize an automated radiolabeling process by evaluating the influence of different key parameters on radiochemical purity and radiochemical yield.

METHODS

The radiosynthesis of [Ga]Ga PSMA-11 was performed using a Trasis MiniAio synthesizer and a Ge/Ga GalliaPharm generator supplied by Eckert & Ziegler, Berlin, Germany. Optimized labeling parameters were evaluated by variation of sodium acetate concentrations and temperature of radiolabeling as well as the purification process.

RESULTS

For each condition tested, radiochemical purity was higher than 99% in the final vial without batch failure, indicating a robust and fast radiosynthesis process. Radiosynthesis without the solid phase extraction purification process at room temperature in less than 5 min resulted in a radiolabeling efficiency of over 99% and remained stable at least 4 h without manual processing to limit operator radiation exposure.

CONCLUSION

The procedure was completely automated and provided a high radiochemical yield. It can be performed several times a day, facilitating the clinical demand of this radiopharmaceutical.

Recovery of EDTA from soil-washing wastewater with calcium-hydroxide-enhanced sulfide precipitation

It is cost effective and thermodynamically feasible to recover EDTA and remove potential toxic elements (PTEs) with sulfide precipitation from soil-washing wastewater produced from EDTA washing PTEs-contaminated soil. However, poor solid-liquid separation and EDTA recovery restrict its application due to a large number of fine particles formed during the precipitation process. This study investigated the effect of single factor on PTEs (Cu, Pb, Cd, and Zn) removal and solid-liquid separation from wastewater. The results showed that Zn was the most difficult to remove compared with Cu, Pb, and Cd; with the aid of Ca(OH)₂, Zn removal efficiency was improved from 22.16% to 92.45%, and over 70.98 min, its average rate was 4.2 times that obtained without Ca(OH)₂ dosage; undissolved Ca(OH)₂ adsorbed suspended particles, acted as condensation nucleus, and promoted similar flocculation effect (self-flocculation); dissolved Ca(OH)₂ modified the charge on the surface of suspended particles by changing the zeta potential from -36.77 ± 1.2 mV to -25.39 ± 3.06 mV and weakened the electrostatic repulsion between the suspended particles, and promoted their adsorption and flocculation precipitation, thereby improving the solid-liquid separation. The acid-recovered EDTA was analyzed in the protonated form (H₄EDTA) using Fourier transform infrared (FT-IR) spectroscopy, and it maintained the same ability to extract PTEs from the soil as that of fresh EDTA over several cycles. This indicates that Ca(OH)₂-enhanced sulfide precipitation can effectively treat soil-washing wastewater and recover EDTA and potentially reduce the cost of remediation techniques for PTEs-contaminated soil with EDTA-enhanced soil washing.

Effect of calcination temperature on the properties of Ti/SnO2-Sb anode and its performance in Ni-EDTA electrochemical degradation

Pd-doped Ti/SnO₂-Sb anode was prepared at different calcination temperatures by a wet-impregnation method and employed in simultaneous electrochemical catalytic degradation of Ni-EDTA and recovery of nickel. The results showed that Ti/SnO₂-Sb-Pd-500 could achieve the highest electrochemical activity (87.5% of Ni-EDTA removal efficiency), superior durability (50.7 h of accelerated lifetime), and higher Ni recovery (19.8%) on cathode. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) analysis suggested that Ni-EDTA degradation on anode was mainly indirect oxidation-controlled reaction, attributing to the high oxide state of MO_X + 1 and MO_X(·OH), rather than direct oxidation. Scanning electron microscope (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses indicated that calcination temperature could modify the morphology of electrode surface and affect the incorporation and valence state transformation of metal species (Sb and Pd) in SnO₂ lattice. Ti/SnO₂-Sb-Pd-500 achieved the highest electrochemical capacity with the highest levels of adsorbed oxygen O_ads/E_T (27.11%) and lattice oxygen O_lat/E_T (29.69%). Moreover, the operation conditions for Ni-EDTA electrochemical degradation were optimized. These findings were valuable for developing a high-performance electrode for Ni-EDTA electrochemical degradation.

Efficient removal of EDTA-complexed Cu(II) by a combined Fe(III)/UV/alkaline precipitation process: Performance and role of Fe(II)

Efficient removal of heavy metal-EDTA complexes from water remains a challenge because of their good solubility and chemical stability. Herein, we employed a proprietary process, i.e., the Fe(III) displacement/UV irradiation/alkaline precipitation (denoted as Fe(III)/UV/OH), to enable an efficient removal of Cu(II)-EDTA complex from 19.2 mg Cu(II)/L to <1 mg Cu(II)/L. The combined process includes Fe(III) replacement with the complexed Cu(II) to form Fe(III)-EDTA and release the free Cu(II), UV-mediated catalytic decarboxylation of EDTA to form amine ligands and reduction of Fe(III) to Fe(II), and the final removal of Cu(II) through precipitation. The in situ formed Fe(II) is crucial to the final Cu(II) removal because it tends to form stable complexes with amine ligands (EDTA and its decarboxylation products), thereby inhibiting their re-complexation with the released Cu(II) and facilitating the formation of copper precipitates. Consequently, the methods capable of prolonging the life of Fe(II), e.g., increasing the Fe(III) addition or direct addition of Fe(II) into the Cu(II)-EDTA solution and deoxygenating the solution, could dramatically enhance the final Cu(II) removal. We also optimized the operational conditions of the process at the initial Cu(II)-EDTA of 19.2 mg Cu(II)/L.

Drawbacks of Dialysis Procedures for Removal of EDTA

Ethylenediaminetetraacetic acid (EDTA) is a chelating agent commonly used in protein purification, both to eliminate contaminating divalent cations and to inhibit protease activity. For a number of subsequent applications EDTA needs to be exhaustively removed. Most purification methods rely in extensive dialysis and/or gel filtration in order to exchange or remove protein buffer components, including metal chelators. We report here that dialysis protocols, even as extensive as those typically employed for protein refolding, may not effectively remove EDTA, which is reduced only by approximately two-fold and it also persists after spin-column gel filtration, as determined by NMR and by colorimetric methods. Remarkably, the most efficient removal was achieved by ultrafiltration, after which EDTA became virtually undetectable. These results highlight a potentially widespread source of experimental variability affecting free divalent cation concentrations in protein applications.

Membrane bioreactor treatment of a simulated metalworking fluid wastewater containing ethylenediaminetetraacetic acid and dicyclohexylamine

Membrane bioreactors (MBRs) have been installed at automotive plants to treat metalworking fluid (MWF) wastewaters, which are known to contain toxic and/or recalcitrant organic compounds. A laboratory study was conducted to evaluate treatment of a simulated wastewater prepared from a semisynthetic MWF, which contains two such compounds, dicyclohexylamine (DCHA) and ethylenediaminetetraacetic acid (EDTA). Primary findings were as follows: During stable operating periods, almost all chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), and EDTA were removed (by > 96%). During somewhat unstable periods, COD removal was still extremely robust, but removal of EDTA and TKN were sensitive to prolonged episodes of low dissolved oxygen. Nitrogen mass balance suggested 30 to 40% TKN removal by assimilation and 60 to 70% by nitrification (including up to 34% TKN removal via subsequent denitrification). Dicyclohexylamine appeared to be readily biodegraded. Maximum DCHA and EDTA degradation rates between pH 7 and 8 were found. An Arthrobacter sp. capable of growth on DCHA as the sole source of carbon and energy was isolated.

Outer-sphere and inner-sphere ligand protonation in metal complexation kinetics: the lability of EDTA complexes

A generic framework, based on the Eigen mechanism, is formulated to describe the formation/dissociation kinetics of inner-sphere metal complexes that may undergo protonation. In principle, all protonated forms of the ligand contribute to the formation of the precursor outer-sphere complexes, but only the sufficiently stable ones effectively contribute to the overall rate of inner-sphere complex formation. The concepts are illustrated by experimental data for Cd(II)-EDTA complexes. Up to pH 8 the dissociation flux in this system is dominated by the protonated inner-sphere complex, even though it is a very minor component of the equilibrium speciation in bulk solution. The results highlight the importance of distinguishing between the thermodynamically predominant species versus the kinetically relevant ones in considerations of dynamic speciation analysis and bioavailability in natural and engineered systems.

Decontamination of solutions containing EDTA using metallic iron

EDTA removal from solutions using metallic iron was carried out at different values of pH, iron load and concentrations at free access of air and in closed vessels. The EDTA destruction was investigated using chemical and capillary electrophoresis analysis. Fe corrosion was studied voltammetrically and the composition of the precipitate formed was investigated using FT-IR spectroscopy and chemical analysis. The EDTA decomposition is remarkably enhanced by the addition of Cu(II) to the EDTA solutions and access of air. The precipitation of the derivatives of insoluble Fe with EDTA or its decomposition products proceeds along with the destruction of EDTA. In closed systems the main EDTA removal reaction is precipitation with iron ions.

The use of Magallanic peat as non-conventional sorbent for EDTA removal from wastewater

Kraft mills are responsible for large volumes discharges of highly polluted effluents. Application of new bleaching processes (i.e. total chlorine-free (TCF) process) is already a feasible option to reduce environmental impacts. The current trend in the increase in the production of TCF pulp will proportionally increase the consumption of chelating agents. The most commonly used chelants, ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DPTA) are supposed to be relatively persistent substances, poorly degradable in biological treatment facilities and are subsequently considered as environmentally critical compounds. Adsorption could be used as a treatment technique to remove recalcitrant compounds from wastewaters. However, in most cases, sorbent and regeneration costs can make the whole process not economically feasible. The goal of this study was to evaluate the use of Magallanic peat as non-conventional sorbent for EDTA removal from wastewater. Adsorption studies were carried out considering a 2(3) factorial design. pH, temperature and sorbent/sorbate (S/S) relationship effects were evaluated in EDTA adsorption onto Magallanic peat. In addition, adsorption isotherm constants were determined according to the Langmuir and Freundlich models. The results showed that the optimal conditions for EDTA adsorption onto Magallanic peat were 20 degrees C, acid pH (4.0) and a low sorbent/sorbate ratio (0.1/100). At these conditions Magallanic peat showed an adsorption capacity for EDTA (Cs(sat)) of 128.2mg/g, comparable and even better than activated carbon (Cs(sat) 56.5mg/g). EDTA adsorption data at 60 degrees C obtained are not shown due to Magallanic peat degradation phenomena.

Removal of EDTA from low pH printed-circuit board wastewater in a fluidized zero valent iron reactor

Fluidized zero valent iron (ZVI) process was adopted to reduce ethylenediaminetetraacetic acid (EDTA) from low pH printed-circuit board (PCB) wastewater for two reasons: (1) low pH of the wastewater favoring the ZVI reaction; (2) higher ZVI utilization for fluidized process due to abrasive motion of the ZVI. The results showed that the degradation of EDTA was greatly enhanced under acidic pH, longer hydraulic detention time (HRT) and presence of dissolved oxygen (DO). Without addition of oxygen, 65% of EDTA was removed with capacity of 7.33 mg EDTA/g ZVI at pH 2, ZVI dosage of 424 g/L and HRT 10 min. With 6.8 mg/L of DO, 83% of EDTA was reduced with capacity of 19.01 mg EDTA/g ZVI for the same experimental condition. The presence of oxygen/ZVI initiated a Fenton type reaction to reduce EDTA. The end product after EDTA degradation was analyzed by high performance liquid chromoagraphy (HPLC), where propionic acid (C(2)H(5)COOH) was observed, indicating EDTA (oxidation number for carbon is 2) was oxidized to propionic acid (oxidation number for carbon is 3). Nitrogen species was also measured and the nitrogen in EDTA was converted to ammonium instead of nitrate and nitrite.

Coupling of photocatalytic and biological reactors to remove EDTA-Fe from aqueous solution

Degradation of 2.5 mM EDTA-Fe solution was performed in a coupled photocatalytic-biological reactor. The system consists of a photochemical annular reactor filled with TiO2 immobilized on glass Raschig rings coupled with an activated sludge continuous reactor. Around 50% of EDTA degradation was reached after 150 min irradiation. Simultaneously a four-fold increase in biodegradability, measured as BOD5/COD ratio, was observed. The activated sludge is not capable to degrade the complex EDTA-Fe but it removed partially the COD and efficiently the BOD5 of the photochemically treated solution.

Treatment of wastewater containing Cu(II)-EDTA using immobilized TiO2/solar light

The photocatalytic oxidation (PCO) of Cu(II)-ethylene diamine tetra-acetic acid (EDTA), employing immobilized TiO2, under natural sunlight rather than artificial UV light conditions, was investigated at a latitude 38 degrees. The immobilized TiO2 film was prepared using a sol gel process, the crystalline structure of which was identified, by X-ray diffraction analysis, as a mixture of the rutile and anatase forms. The PCO of Cu(II)-EDTA was examined in a circulating reactor with 20 L of 10(-4) M Cu(II)-EDTA and synthetic and real wastewaters at pH 4 and 6.5, respectively. The removals of both Cu(II) and DOC were initially relatively rapid, but slowed as the reaction proceeded and generally followed first-order kinetics. The rate constants for the removal of Cu(II) and DOC were 1.1 x 10(-3) and 1.6 x 10(-3) min-1, respectively. The efficiency of the PCO in the decomplexation of Cu(II)-EDTA increased with increasing H2O2 dose using both the synthetic and real wastewaters. Therefore, we suggest the PCO process using the solar/immobilized TiO2 system, with addition of H2O2 as well as filtration for the removal of suspended solids, can be effectively applied to the treatment of Cu(II)-EDTA containing real wastewater.

Oxidation of aqueous EDTA and associated organics and coprecipitation of inorganics by ambient iron-mediated aeration

Cationic metal and radionuclide contaminants can be extracted from soils to groundwater with sequestering agents such as EDTA. However, EDTA must then be removed fromthe groundwater, by advanced oxidation or specialized biological treatment. In this work, aqueous individual metal-EDTA solutions were aerated with steel wool for 25 h, at ambient pH, temperature, and pressure. Removal of approximately 99% of EDTA (0.09-1.78 mM); glyoxylic acid (0.153 mM); chelated Cd2+ (0.94 and 0.0952 mM), Pb2+ (0.0502 mM), and Hg2+ (0.0419 mM); and free chromate and vanadate was shown. EDTA was oxidized to glyoxylic acid and formaldehyde, and metals/metalloids were coprecipitated together with iron oxyhydroxide floc. Free arsenite and arsenate were each removed at 99.97%. Free Sr2+, and chelated Ni2+ were removed at 92% and 63%, respectively. Similar removals were obtained from mixtures, including 99.996+/-0.004% removal of total arsenic (95% confidence). Traces of iminodiacetic acid, nitrilotriacetic acid, and ethylenediaminetriacetic acid were detected after 25 h. Results are consistent with first-order, solution-phase oxidation of EDTA and glyoxylic acid by ferryl ion and H202, respectively, with inhibition due to sludge accumulation, and equilibrium metal coprecipitation. This ambient process, to our knowledge previously unknown, agrees with recently reported findings and shows promise for remediation of metals, metalloids, and radionuclides in wastewater, soil, and sediment.

Removal of Cu(II)-EDTA complex using TiO2/solar light: the effect of operational parameters and feasibility of solar light application

The photocatalytic oxidation (PCO) of Cu(II)-ethylene diamine tetra acetic acid (EDTA) was investigated at 38 degrees latitude, using natural sunlight instead of artificial UV light. In order to investigate the optimum conditions for the PCO of Cu(II)-EDTA, the effects of several parameters, such as the type and angle of solar collector, solar light intensity, area of the solar reactor and flow rate, on the removals of Cu(II) and dissolved organic carbon (DOC) were examined with 20 L of 10(-4) M Cu(II)-EDTA at pH 4 in a circulating reactor. The removals (%) of Cu(II) and DOC were favorable with the use of a hemispherical collector, with a 38 degrees tilt angle when flat, on a sunny day, and a solar collector with a high area, in a TiO(2) slurry system. On the basis of these experimental results, PCO with solar light irradiation could be used as a feasible technique in the treatment of Cu(II)-EDTA. In addition, PCO with solar light irradiation is regarded as a potential technique in the treatment of real electroplating wastewater when considering the quite similar removal efficiency of Cu(II)-EDTA, with the subsequent removal of the liberated Cu(2+) by adsorption onto the TiO(2) compared to that of synthetic wastewater.

Removal of Pb from a calcareous soil during EDTA-enhanced electrokinetic extraction

Electrokinetic extraction has been tested to remove lead from an Algerian contaminated soil ([Pb] = 4.432 +/- 0.275 mg g(-1)) sited near a battery plant. The effect of EDTA at various concentrations (0.05-0.20 M) on the enhancement of lead transport has been studied by applying a constant voltage corresponding to a nominal electric field strength of 1 V cm(-1) (duration: 240 h). Results of contaminant distribution across the experimental cell have shown efficient transport of lead toward the anode despite the presence of calcite (25%) and the high acid/base buffer capacity of the soil. To avoid ligand loss, which would be anodically oxidized, the cell was modified by adding extra compartments and inserting cation exchange membranes (Neosepta CMX). Thus, simultaneous recovery of EDTA and lead from their chelated solutions has been made possible using the same set-up and by controlling fluids chemistry.

Enzymatic versus nonenzymatic conversions during the reduction of EDTA-chelated Fe(III) in BioDeNOx reactors

Reduction of EDTA-chelated Fe(III) is one of the core processes in the BioDeNOx process, a chemically enhanced technique for biological NOx removal from industrial flue gases. The capacity of Escherichia coli, three mixed cultures from full scale methanogenic granular sludge reactors, one denitrifying sludge, and a BioDeNOx sludge to reduce Fe(III)EDTA- (25 mM) was determined at 37 and 55 degrees C using batch experiments. Addition of catalytic amounts of sulfide greatly accelerated Fe(III)EDTA- reduction, indicating that biological Fe(III)EDTA- reduction is not a direct, enzymatic conversion but an indirect reduction with involvement of an electron-mediating compound, presumably polysulfides. It is suggested that not thermophilic dissimilatory iron-reducing bacteria but reducers of elemental sulfur or polysulfides are primarily involved in the reduction of EDTA-chelated Fe(III) in BioDeNOx reactors.

Recovery of EDTA from complex solution using Cu(II) as precipitant and Cu(II) subsequent removal by electrolysis

Ethylendiaminetetraacetate (EDTA) is a chelating agent widely used in industry and agriculture. Resistant to chemical and biological degradation EDTA represents a serious ecological problem. In order to avoid the outlet into the environment a new method of EDTA recycling has been proposed. The method involves substituting of the metal ions in EDTA complexes by Cu(II) and formation of an insoluble Cu2EDTA.4H2O compound at the excess of Cu(II) ions in weakly acidic solutions. Cu(II) ions substitute such metal ions as Ni(II), Zn(II), Co(II), Cd(II), Ca(II) and Mg(II). After treatment of the precipitate with water only, acidic or alkaline solutions the copper from the suspension formed can be removed by electrolysis. The highest current efficiency under galvanostatic conditions is in alkaline solutions, however, the highest yield of EDTA recovery is in acidic solutions. FT-IR investigations and chemical analysis of the precipitate formed have shown that in acidic and in alkaline solutions, H4EDTA and Na2H2EDTA.2H2O were formed, respectively. Electrolysis in acidic solutions gives the best results, i.e. the formed H4EDTA contains the highest amount of EDTA (95%) and the lowest amount of copper (0.01%).

Removal of EDTA by UV-C/hydrogen peroxide

Mineralization of a 5 mM EDTA solution at pH 3 was evaluated via TOC removal under UV-C irradiation in the presence of H2O2 at various conditions. The highest TOC removal (78%) was obtained using a 40:1 H2O2/EDTA molar ratio, after 540 min irradiation. However, a 20:1 ratio gave slightly lower results, being economically more attractive. Best results of TOC removal were obtained under pH controlled conditions. Addition of TiO2 (1 g l(-1)) was detrimental, even in the presence of H2O2, indicating that at this concentration, TiO2 inhibits the mineralization, probably by scattering or by screening of the light.

Separation selectivity of anionic metal complexes of N,N'-bis(hydroxybenzyl)ethylenediamine-N,N'-diacetic acid in ion and ion electrokinetic chromatography

The complexes of Fe(III), Co(III), Mn(III), Al(III), Cu(II), Ni(II), Cd(II) and Zn(II) with N,N'-bis(hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED) were separated by ion exchange in different modes: ion chromatography (IC) and ion electrokinetic chromatography (IEKC). In column IC these complexes were separated on an IonPac AS4a anion-exchange column (Dionex, USA). Parameters of the background electrolyte that were examined in IEKC mode include polymer, competing ion concentration and pH. The use of poly(diallyldimethylammonium chloride) (PDADMACl) as a modifier in IEKC provides separation selectivity only slightly different from that observed in IC on the IonPac AS4a column. Optimal separation conditions were found to be: 0.1 mM HBED, 50 mM PDADMAOH, 10 mM Na2 B4 O7, pH adjusted to 10 with acetic acid. The use of an aromatic ligand allowed a 10-fold decrease in detection limits of metal ions in comparison with previously studied EDTA. A separation efficiency up to 400,000 theoretical plates was demonstrated for IEKC.

Thiol-reactive, luminescent Europium chelates: luminescence probes for resonance energy transfer distance measurements in biomolecules

Lanthanide chelates have recently been shown to be extremely promising luminescence probes for distance measurements in biomolecules using luminescence resonance energy transfer measurements [P. R. Selvin, T. M. Rana, and J. E. Hearst (1994) J. Am. Chem. Soc. 116, 6029-6030; P. R. Selvin, and J. E. Hearst (1994) Proc. Natl. Acad. Sci. USA 91, 10024-10028]. In this work we describe simple procedures for preparing highly fluorescent thiol-reactive europium chelates. These new compounds contain a uv-absorbing coumarin group which sensitizes europium emission, diethylenetriaminepentaacetic acid or triethylenetetraaminehexaacetic acid groups which provide europium chelating function, and a pyridyl disulfide group which allows specific modification of thiol groups. These reagents can be used to label proteins at Cys residues or synthetic oligonucleotides which contain thiol groups. Modification can be reversed easily by treatment with a reducing agent (dithiothreitol). Luminescence energy transfer between these new chelates and CY5 fluorochrome attached to the opposite ends of 15-bp double-stranded DNA was measured to test their usefulness for distance measurements in macromolecules. The distance measured between the chelate (donor) and CY5 (acceptor) was in the range expected for the length of 15-bp DNA. The stability of europium chelates and their conjugates with a protein, the precision of distance measurements using these chelates, possible errors due to intramolecular energy transfer, and the modulation of the R0 value with deuterium oxide were tested. The results obtained fully confirmed the great potential of these new probes for sensitive, simple, and precise distance measurements in biomolecules using luminescence resonance energy transfer.

Low-level determination of ethylenediaminetetraacetic acid in complex matrices

A method for the determination of ethylendiaminetetraacetic acid (EDTA) in foodstuffs by high performance liquid chromatography (HPLC) and gas chromatography (GC) is described. This method is applied to foodstuffs rich in sugars and polysaccharides for which aqueous extraction cannot be directly used in chromatographic analysis. EDTA, in its iron chelate form, is extracted with water from the defatted foodstuff. The extract is then purified by ion-exchange chromatography. At this stage of purification, the quantitative level of EDTA can be estimated by HPLC and the result can be confirmed by GC. The detection level of our samples of tinned beans was under 5 mg/kg.

Identification of artifactual cathepsin D activity in cardiac subcellular fractions related to formation of an iron-EDTA complex

The conventional assay procedure for cathepsin D (E.C.3.4.23.5) activity in tissue homogenates and subcellular fractions requires incubation with hemoglobin as substrate. Cathepsin D (CD) activity is calculated by determining the increase in absorbance at 280 nm after precipitation of all proteins with trichloroacetic acid. This increase in absorbance (presumably due to the release of tyrosine residues from hemoglobin) is converted to arbitrary CD activity units. Homogenization and fractionation of cardiac tissue frequently requires that ethylenediamine tetraacetic acid (EDTA) be included in the homogenization medium. We have observed that subcellular fractions of cardiac tissue prepared in the presence of EDTA demonstrate residual CD activity despite either quantitative removal of all CD protein by immunoprecipitation or complete inhibition of CD by pepstatin. The present study demonstrates that this 'apparent' CD activity (residual increase in absorbance at 280 nm) is due to the formation of an Fe-EDTA complex which absorbs at 280 nm. Data are presented which demonstrates that the EDTA of the medium complexes with non-heme iron which contaminates commercially available hemoglobin. A method for preparing hemoglobin free of contaminant non-heme iron is described for use in studies of CD metabolism when EDTA is present in the homogenization buffer.