Radioactive Form Research Articles

Experimental estimates of hygroscopic growth of particulate fission product species (mixed CsI–CsOH) with implications in reactor accident safety research

Studies on severe nuclear reactor accidents consider CsI and CsOH as the two predominant forms of cesium expected to be released following a reactor accident; 137Cs, 134Cs and 131I being their dominant radioactive forms. Recent studies have measured the hygroscopic growth factors (HGF) and activation fractions for laboratory generated CsI and CsOH particles in sub-saturation and super-saturation relative humidity environments. This work measures and compares the HGF of mixed CsI–CsOH particles with those of individual components. The experiments have been performed with hygroscopic tandem differential mobility analyser for varying mass ratios (w/w) of CsI: CsOH and the results have been compared with the theoretical estimates made using Brechtel and Kredneweis (2000) theory in conjugation of ZSR (Zdanovskii–Stokes–Robinson) mixing rule. The study shows different behavioural pattern of hygroscopic growth of mixed particles in comparison to individual components. A clear transitional change in the growth factor patterns was observed for the ratio below 1:1. Additionally, the experiments to study the effect of different dry diameters (50, 100, 150 and 200 nm) for 1:1 ratio revealed that hygroscopic growth was independent of initial dry diameter. Effect of dehydration for 3 mixing ratios viz., 1:02, 1:1 and 1:10 showed continuous pattern indicating the dominance of CsOH. Terminal settling velocities for the mixed and individual particles are compared for highlighting the probable impact on surface deposition flux calculations. The aerosol hygroscopic growth of mixed CsI–CsOH particles has direct implications in improving source term estimates for a severe reactor accident safety analysis.

Addition of transition metal oxides on silver tellurite glass for radioactive iodine immobilization

The long-lived radioactive forms of iodine pose significant environmental threats. Therefore, it is important to capture and immobilize radioactive iodine. In this study, an iodine immobilization matrix was developed and investigated by adding transition metal oxides such as WO3, MoO3, and V2O5 to the AgI-Ag2O-TeO2 glass system. The immobilization was confirmed by melting the glass precursor mixtures at 800°C for 1 h without a significant loss of the elements that comprising the glass. The loading of iodine in the matrix was approximately 13-15% by weight, excluding elemental oxygen. The normalized releases of all the elements obtained by PCT-A were below 10−1 g/m2, thereby satisfying the USA regulations (2 g/m2). The structural factors related to the chemical durability of the glass were discussed. The addition of WO3, MoO3, and V2O5 suppressed the release of iodine by densifying the TeO4 polyhedra. The silver release was not significantly affected by increasing the concentrations of the transition metal oxides. The additives stabilized tellurium, which is a glass network former, to prevent its release from the glass matrix. All the transition metals considered in this study remained stable in the silver tellurite glass in comparison to the release of tellurium.

Hydroxyapatite (Ha) labeling with a phosphorus-32 radioisotope of the TRIGA 2000 reactor irradiation result as a candidate for radiosinovectomy therapy

Radiosynovectomy is a therapy performed on patients with acute-level arthritis (rheumatoid arthritis) as an alternative solution besides surgery. Radiosynovectomy is performed using a labeled compound with a particle size of 0.5-10 μm labeled with a β radioisotope. Hydroxyapatite (HA) is a 1-10 μm-sized compound found in bones with the components of Calcium (Ca) & Phosphorus (P). Phosphorus-32 (32P) is a radioactive form of Phosphorus which emits pure beta rays and is often used for therapy. Labelling HA with 32P tends to be easy to do with a substitution reaction, because phosphorus is the main constituent of HA. Phosphorus-32 was made by irradiating natural sulfur at the Bandung TRIGA 2000 reactor facility following the 32S (n, p) 32P reaction mechanism. The separation process of Phosphorus-32 was carried out by a distillation method followed by extraction with 0.01 N HCl accompanied by heating for 30 minutes. The Phosphorus-32 solution is then passed through a 3 gr cation exchange resin. Before Phosphorus-32 was used for Labelling of HA, a Radionuclide Purity test was performed with a gamma-MCA spectrophotometer and a Radiochemical Purity test using paper chromatography. The test results showed Phosphorus-32 had Radionuclide Purity > 99.99% and Radiochemical Purity > 96%. 0.5 mCi Phosphorus-32 which meets the quality test requirements is reacted with 7 mg Ha at pH 7. Then it is vortexed at 1500 rpm for 60 minutes with 70 ° C heating. HA-32P is separated using centrifugation into residual and supernatant fractions. Measure the radioactivity of both fractions with a dose calibrator. Labeling Yield HA with Phosphorus-32 was obtained 98%. Furthermore this HA is ready to be used in in vivo tests for radiosynovectomy.

Neutron Activated 153Sm Sealed in Carbon Nanocapsules for in Vivo Imaging and Tumor Radiotherapy.

Radiation therapy along with chemotherapy and surgery remain the main cancer treatments. Radiotherapy can be applied to patients externally (external beam radiotherapy) or internally (brachytherapy and radioisotope therapy). Previously, nanoencapsulation of radioactive crystals within carbon nanotubes, followed by end-closing, resulted in the formation of nanocapsules that allowed ultrasensitive imaging in healthy mice. Herein we report on the preparation of nanocapsules initially sealing "cold" isotopically enriched samarium (152Sm), which can then be activated on demand to their "hot" radioactive form (153Sm) by neutron irradiation. The use of "cold" isotopes avoids the need for radioactive facilities during the preparation of the nanocapsules, reduces radiation exposure to personnel, prevents the generation of nuclear waste, and evades the time constraints imposed by the decay of radionuclides. A very high specific radioactivity is achieved by neutron irradiation (up to 11.37 GBq/mg), making the "hot" nanocapsules useful not only for in vivo imaging but also therapeutically effective against lung cancer metastases after intravenous injection. The high in vivo stability of the radioactive payload, selective toxicity to cancerous tissues, and the elegant preparation method offer a paradigm for application of nanomaterials in radiotherapy.

Dosimetry of Nano-Radio-Ytterbium Therapy by MIRD and MCNP methods for humans’ organs

Introduction: Nano radio-pharmaceutical therapy (NRPT) is a new method for solid tumor therapy. The treatment uses a radioactive form of radionuclide encapsulated in the poly amido amine dendrimers. The poly (amidoamine) (PAMAM) dendrimers have attracted attentions for cancer treatment by their characteristics of targeted drug carriers, delivery agents, and imaging agents in human systems. We have reported the preparation of dendrimer encapsulated ytterbium-175 radio- nanoparticles and its biodistribution in tumor bearing rats.175Yb (T1/2=4.2 days), decays to stable 175Lu with a β- emitter with 470 keV maximum energy (86.5%) and γ photons of 113 keV (1.9%), 282keV (3.1%) and 396 keV (6.5%) that are appropriate for imaging. This paper aims at comparing dosimetric assessments in human performed with Monte Carlo codes and MIRD based on the experimental results of biodistribution of dendrimer encapsulated ytterbium-175.Materials and Methods: All chemical materials including, Ytterbium (III) oxide (Yb2O3), PAMAMG5-NH2 dendrimer in 5% methanol solution and HNO3, Sodium boro- hydride (NaBH4) were purchased from Sigma Aldrich Chemical Co. USA and Merck, Germany. For biodistribution study 20 female Balb/c mice were purchased from Pasteur Institute of Iran. To estimate the absorbed dose by both methods, MCNP and MIRD, the cumulated activity in source organs were calculated by the percentage of injected dose in humans’ organs. The residence times (τ) in the source organs were obtained by integration of respective fit functions, on biokinetics curve, after accounting for the physical decay of the 175Yb. The dose calculation was done for a certain group of organs of human following the MIRD technique. To simulate the problem with MCNP, the ORNL phantom was used. The desired result for this study is absorbed doses of vital organs (liver, spleen, lung and kidney). Results: The maximum uptake of radio-compound are in the liver, lung and spleen. The biodistribution shows the characteristics of nanoparticles such as size and surface hydrophobicity that determine the amount of adsorbed radiopharmaceuticals in organs. The initial fast distribution of radiotracer is throughout liver, lung, and Bone, with slower accumulation in blood and spleen. The result of 2 methods (MIRD versus MCNPX) reveals that MIRD underestimate the absorbed dose for bladder, bone, lung, and ovaries while overestimate for liver, muscle and spleen. In this study the absorbed dose from 175Yb- PAMAM estimated by MCNPX for liver, lung, spleen, kidney and bone are 1.266, 8.081E-01, 8.347E-01, 3.979E-02 and 1.706E-02 mGy/MBq respectively Conclusion: Owing to the stability of PAMAM encapsulated Yb-175 and the size of nano- particle the concentrations are mostly in liver and lungs. State of- the-art dosimetry depends on the duration of the biokinetics of the radiopharmaceutical and a calculation of residence times including an analysis of the errors associated with the respective calculation that aimed in this study. The results showed that this nano-radiopharmaceutical has potential of application for liver and lung tumors.

Screening of candidate substrates and coupling ions of transporters by thermostability shift assays.

Substrates of most transport proteins have not been identified, limiting our understanding of their role in physiology and disease. Traditional identification methods use transport assays with radioactive compounds, but they are technically challenging and many compounds are unavailable in radioactive form or are prohibitively expensive, precluding large-scale trials. Here, we present a high-throughput screening method that can identify candidate substrates from libraries of unlabeled compounds. The assay is based on the principle that transport proteins recognize substrates through specific interactions, which lead to enhanced stabilization of the transporter population in thermostability shift assays. Representatives of three different transporter (super)families were tested, which differ in structure as well as transport and ion coupling mechanisms. In each case, the substrates were identified correctly from a large set of chemically related compounds, including stereo-isoforms. In some cases, stabilization by substrate binding was enhanced further by ions, providing testable hypotheses on energy coupling mechanisms.

Epoxidation of Carbon Nanocapsules: Decoration of Single-Walled Carbon Nanotubes Filled with Metal Halides.

Methyl(trifluoromethyl)dioxirane (TFDO) can be used for the oxyfunctionalization of SWCNTs filled with NaI and LuCl3 under mild conditions. The chosen metal halides are of interest for theranostics, both for imaging and therapy when in their radioactive form. The applied functionalization methodology does not require metal catalyst, preserves the integrity of the nanotubes during treatment, avoiding the release of the filling material. In this way, epoxidation can be considered as an efficient methodology for the functionalization of carbon nanocapsules, where the traditional harsh oxidation conditions by acids are not applicable.

Isoconcentration principle – an effective tool of (radio) analysis in environmental protection

The paper brings two determination methods for non-radioactive analytes based on isoconcentration principle. The first method represents a determination procedure for a non-radioactive substance by use of its radio-labelled form of known concentration by help of a (non-quantitative, but selective) separation method. The main advantage of this method consists in the fact, that the determination is executable only by the detection of radioactivity. The second described procedure enables the determination of the chosen analyte without requirement of radioactive form of the substance to be determinate.

Diffusion coupling in multiply associating electrolyte solutions

Diffusion coupling in multiply associating aqueous electrolyte solution is studied. The process is illustrated in the case of zinc(II) ion which forms a set of complexes, ZnCln2−n (with n=1,..,4), in the presence of chloride ions. The transport of zinc ion, taken in radioactive form 65Zn2+, in the electric field created by a gradient of LiCl, is investigated experimentally by employing an adaptation of the closed capillary technique. The transient diffusion process is modeled by using two different treatments: finite difference (FD) simulation and normal-mode (NM) analytic solution. Deviations from ideality are taken into account with the use of the mean spherical approximation (MSA), and the internal electric field is calculated using the dynamical electroneutrality condition. The theoretical FD and NM results are compared with the experimental data about the diffusion of zinc.

The discovery of T cell-B cell cooperation.

The discovery of T cell-B cell cooperation.

The influence of mineral variability of Callovo-Oxfordian clay rocks on radionuclide transfer properties

The upper part of the Callovo-Oxfordian clay-rich rock formation (C2c unit) (Meuse/Haute-Marne, France) displays large variations in mineralogical composition of quartz, carbonate and clay minerals. This study deals with the effects of this composition variability on the diffusion-dominated transport properties of HTO (tritiated water)33Tritiated water is a radioactive form of water where some usual hydrogen atoms are replaced with tritium., 36Cl− and 137Cs+ for these rocks. Effective diffusion coefficients De and accessible porosities ε were determined using the through-diffusion method for a set of C2c unit samples characterized by a contrasted mineralogy especially in terms of clay mineral content (4–29%).The relative variations of the effective diffusion coefficients measured for HTO, 36Cl− and 137Cs+ remain limited within a range of a factor 5 down to a clay mineral content of ~10%. In the range of clay mineral content higher than 15%, the effective diffusion coefficient tends to increase for 137Cs+ and decreases for 36Cl− whereas De(HTO) stays relatively stable. Anion exclusion and surface enhanced diffusion for caesium were quantified and can explain this behaviour. Below 10% of clay minerals, these effective coefficients and the accessible porosities decreased drastically. For 4% of clay minerals, De were equal to 1.3·10−12m2s−1 for HTO, 3.5·10−13m2s−1 for 36Cl− and 7·10−12m2s−1 for 137Cs+. One of the main findings is that the anion exclusion and the enhanced diffusion for caesium still occur for the samples characterized by the lowest clay mineral contents. Finally, the set of diffusion data has been analysed against the well-known Archie's relation linking the accessible porosity to the effective diffusion coefficient.

Semisynthesis of Radiolabeled Amino Acid and Lipid Brevetoxin Metabolites and Their Blood Elimination Kinetics in C57BL/6 Mice

Brevetoxin B (BTX-B), produced by dinoflagellates of the species Karenia, is a highly reactive molecule, due in part to an α,β-unsaturated aldehyde group at the terminal side chain, leading to the production of metabolites in shellfish by reduction, oxidation, and conjugation. We have investigated in mice the blood elimination of three common bioactive brevetoxin metabolites found in shellfish, which have been semisynthesized from BTX-B in radioactive forms. BTX-B was reduced at C42 to yield [(3)H] dihydro-BTX-B. [(3)H] S-desoxy-BTX-B2 (cysteine brevetoxin B) was semisynthesized from BTX-B by the conjugation of cysteine at the C50 olefinic group then [(3)H] radiolabeled by C42 aldehyde reduction. [(14)C] N-Palmitoyl-S-desoxy-BTX-B2 was prepared using S-desoxy-BTX-B2 as the starting material with addition of the [(14)C] radiolabeled fatty acid via cysteine-amide linkage. The elimination of intravenously administered [(3)H] S-desoxy-BTX-B2, [(14)C] N-palmitoyl-S-desoxy-BTX-B2, or [(3)H] dihydro-BTX-B was measured in blood collected from C57BL/6 mice over a 48 h period. Each brevetoxin metabolite tested exhibited biexponential elimination kinetics and fit a two-compartment model of elimination that was applied to generate toxicokinetic parameters. The rate of transfer between the central compartment (i.e., blood) and the peripheral compartment (e.g., tissue) for each brevetoxin differed substantially, with dihydro-BTX-B exchanging rapidly with the peripheral compartment, S-desoxy-BTX-B2 eliminating rapidly from the central compartment, and N-palmitoyl-S-desoxy-BTX-B2 eliminating slowly from the central compartment. Toxicokinetic parameters were analyzed in the context of the unique structure of each brevetoxin metabolite resulting from a reduction, amino acid conjugation, or fatty acid addition to BTX-B.

Unknown Quantity: Regulating Radionuclides in Tap Water

Radioactivity surrounds us; each day we are exposed to a certain amount by virtue of being alive on planet Earth. Some of this exposure comes from radioactive substances (radionuclides) that occur naturally in a wide variety of geologic and soil formations. Occasionally these naturally occurring substances become more concentrated or accessible through human activities such as mining and nuclear energy production, resulting in greater potential for exposure than their original natural occurrence would suggest. Other radionuclides are artificially created. Residents in almost all parts of the United States live on lands that contain minor to substantial concentrations of radionuclides of one type or another.1 These substances often make their way into tap water, leading to exposures by ingestion, inhalation, or dermal pathways during showering or other contact with the water. Although radionuclides are widespread, there are large gaps in our knowledge about sources of these materials, their distribution, associated health risks, and mitigation measures. However, the information we do have suggests that current drinking water standards for radionuclides established by the U.S. Environmental Protection Agency (EPA) may not adequately protect health. The EPA is set to review these standards relatively soon, and the next two years are prime time for filling in numerous information gaps and doing other legwork to make sure the review is as well informed as possible.

Colicin M hydrolyses branched lipids II from Gram-positive bacteria

Lipids II found in some Gram-positive bacteria were prepared in radioactive form from l-lysine-containing UDP-MurNAc-pentapeptide. The specific lateral chains of Enterococcus faecalis, Enterococcus faecium and Staphylococcus aureus (di-l-alanine, d-isoasparagine, and pentaglycine, respectively) were introduced by chemical peptide synthesis using the Fmoc chemistry. The branched nucleotides obtained were converted into the corresponding lipids II by enzymatic synthesis using the MraY and MurG enzymes. All of the lipids were hydrolysed by Escherichia coli colicin M at approximately the same rate as the meso-diaminopimelate-containing lipid II found in Gram-negative bacteria, thereby opening the way to the use of this enzyme as a broad spectrum antibacterial agent.

A review and model assessment of 32P and 33P uptake to biota in freshwater systems

Bioaccumulation of key short-lived radionuclides such as 131I and 32,33P may be over-estimated since concentration ratios ( CRs) are often based on values for the corresponding stable isotope which do not account for radioactive decay during uptake via the food chain. This study presents estimates for bioaccumulation of radioactive phosphorus which account for both radioactive decay and varying ambient levels of stable P in the environment. Recommended interim CR values for radioactive forms of P as a function of bioavailable stable phosphorus in the water body are presented. Values of CR are presented for three different trophic levels of the aquatic food chain; foodstuffs from all three trophic levels may potentially be consumed by humans. It is concluded that current recommended values of the CR are likely to be significantly over-estimated for radioactive phosphorus in many freshwater systems, particularly lowland rivers. Further research is recommended to field-validate these models and assess their uncertainty. The relative importance of food-chain uptake and direct uptake from water are also assessed from a review of the literature. It can be concluded that food-chain uptake is the dominant accumulation pathway in fish and hence accumulation factors for radioactive phosphorus in farmed fish are likely to be significantly lower than those for wild fish.

Tritium in the Environment of Gulf of Finnland

Tritium is a radioactive form of hydrogen, used in research, fusion reactors and neutron generators. The form of most concern, tritium oxide (HTO), is generally indistinguishable from normal water and can move rapidly through the environment in the same manner as water. The expanding construction of nuclear industrial plants and nuclear power stations on the shores of the Baltic Sea (Gulf of Finnland) is creating a real possibility for the introduction of radioactive wastes into the vegetation and the waters of Baltic Sea basin (Sea water, Ladoga Lake, St.Petersburg rivers). A low-level liquid scintillation system Quantulus 1220 (Wallac, Turku, Finland) and system for sample preparation Sample Oxidizer 307 (PerkinElmer) were used for measurements of vegetation and water samples from this region. Significant difference was observed on the distribution of tritium concentrations in different types of water, snow cover and vegetation of Finnish Bay basin.

Human Health and the Biological Effects of Tritium in Drinking Water: Prudent Policy Through Science - Addressing the ODWAC New Recommendation.

Tritium is a radioactive form of hydrogen and is a by-product of energy production in Canadian Deuterium Uranium (CANDU) reactors. The release of this radioisotope into the environment is carefully managed at CANDU facilities in order to minimize radiation exposure to the public. However, under some circumstances, small accidental releases to the environment can occur. The radiation doses to humans and non-human biota from these releases are low and orders of magnitude less than doses received from naturally occurring radioisotopes or from manmade activities, such as medical imaging and air travel. There is however a renewed interest in the biological consequences of low dose tritium exposures and a new limit for tritium levels in Ontario drinking water has been proposed. The Ontario Drinking Water Advisory Council (ODWAC) issued a formal report in May 2009 in response to a request by the Minister of the Environment, concluding that the Ontario Drinking Water Quality Standard for tritium should be revised from the current 7,000 Bq/L level to a new, lower 20 Bq/L level. In response to this recommendation, an international scientific symposium was held at McMaster University to address the issues surrounding this change in direction and the validity of a new policy. Scientists, regulators, government officials, and industrial stakeholders were present to discuss the potential health risks associated with low level radiation exposure from tritium. The regulatory, economic, and social implications of the new proposed limit were also considered.The new recommendation assumed a linear-no-threshold model to calculate carcinogenic risk associated with tritium exposure, and considered tritium as a non-threshold chemical carcinogen. Both of these assumptions are highly controversial given that recent research suggests that low dose exposures have thresholds below which there are no observable detrimental effects. Furthermore, mutagenic and carcinogenic risk calculated from tritium exposure at 20 Bq/L would be orders of magnitude less than that from exposure to natural background sources of radiation. The new proposed standard would set the radiation dose limit for drinking water to 0.0003 mSv/year, which is equivalent to approximately three times the dose from naturally occurring tritium in drinking water. This new standard is incongruent with national and international standards for safe levels of radiation exposure, currently set at 1 mSv/year for the general public. Scientific research from leading authorities on the carcinogenic health effects of tritium exposure supports the notion that the current standard of 7,000 Bq/L (annual dose of 0.1 mSv) is a safe standard for human health.Policy-making for the purpose of regulating tritium levels in drinking water is a dynamic multi-stage process that is influenced by more than science alone. Ethics, economics, and public perception also play important roles in policy development; however, these factors sometimes undermine the scientific evidence that should form the basis of informed decision making. Consequently, implementing a new standard without a scientific basis may lead the public to perceive that risks from tritium have been historically underestimated. It was concluded that the new recommendation is not supported by any new scientific insight regarding negative consequences of low dose effects, and may be contrary to new data on the potential benefits of low dose effects. Given the lack of cost versus benefit analysis, this type of dramatic policy change could have detrimental effects to society from an ethical, economical, and public perception perspective.

From prophylaxis to atomic cocktail: Circulation of radioiodine

This paper is a history of iodine. To trace the trajectory of this element, goiter is used as a guideline for the articulation of a historical account, as a representation of thyroid disorders and of the spaces of knowledge and practices related to iodine. Iodine's journey from goiter treatment and prophylaxis in the late interwar period took on a new course after WWII by including the element's radioactive isotopes. I intend to show how the introduction of radioiodine contributed to stabilize the epistemic role of iodine, in both its non-radioactive and radioactive form, in thyroid gland studies and in the treatment of its disorders.

Two complementary fluorimetric assays for the determination of aminoquinoline binding and uptake by human erythrocytes in vitro

We provide two simple low-cost and low-tech procedures to measure with good precision and accuracy the binding and internalization into human erythrocytes of chloroquine and other aminoquinolines. The methods are based on the high fluorescence of the quinoline ring and are complementary. Method A evaluates residual drugs in the supernatants of treated erythrocytes, whereas method B quantifies the total uptake by whole cells and the fraction bound to the membranes. Drug uptake is dose dependent and related to the number of erythrocytes. These assays could be useful when studying the cell interaction of quinoline-type compounds not available in the radioactive form.

α-Isopropylmalate, a Leucine Biosynthesis Intermediate in Yeast, Is Transported by the Mitochondrial Oxalacetate Carrier

In Saccharomyces cerevisiae, alpha-isopropylmalate (alpha-IPM), which is produced in mitochondria, must be exported to the cytosol where it is required for leucine biosynthesis. Recombinant and reconstituted mitochondrial oxalacetate carrier (Oac1p) efficiently transported alpha-IPM in addition to its known substrates oxalacetate, sulfate, and malonate and in contrast to other di- and tricarboxylate transporters as well as the previously proposed alpha-IPM transporter. Transport was saturable with a half-saturation constant of 75 +/- 4 microm for alpha-IPM and 0.31 +/- 0.04 mm for beta-IPM and was inhibited by the substrates of Oac1p. Though not transported, alpha-ketoisocaproate, the immediate precursor of leucine in the biosynthetic pathway, inhibited Oac1p activity competitively. In contrast, leucine, alpha-ketoisovalerate, valine, and isoleucine neither inhibited nor were transported by Oac1p. Consistent with the function of Oac1p as an alpha-IPM transporter, cells lacking the gene for this carrier required leucine for optimal growth on fermentable carbon sources. Single deletions of other mitochondrial carrier genes or of LEU4, which is the only other enzyme that can provide the cytosol with alpha-IPM (in addition to Oac1p) exhibited no growth defect, whereas the double mutant DeltaOAC1DeltaLEU4 did not grow at all on fermentable substrates in the absence of leucine. The lack of growth of DeltaOAC1DeltaLEU4 cells was partially restored by adding the leucine biosynthetic cytosolic intermediates alpha-ketoisocaproate and alpha-IPM to these cells as well as by complementing them with one of the two unknown human mitochondrial carriers SLC25A34 and SLC25A35. Oac1p is important for leucine biosynthesis on fermentable carbon sources catalyzing the export of alpha-IPM, probably in exchange for oxalacetate.