The reaction of HOCl and cyanocobalamin: corrin destruction and the liberation of cyanogen chloride

Overproduction of hypochlorous acid (HOCl) has been associated with the development of a variety of disorders such as inflammation, heart disease, pulmonary fibrosis, and cancer through its ability to modify various biomolecules. HOCl is a potent oxidant generated by the myeloperoxidase-hydrogen peroxide-chloride system. Recently, we have provided evidence to support the important link between higher levels of HOCl and heme destruction and free iron release from hemoglobin and RBCs. Our current findings extend this work and show the ability of HOCl to mediate the destruction of metal-ion derivatives of tetrapyrrole macrocyclic rings, such as cyanocobalamin (Cobl), a common pharmacological form of vitamin B12. Cyanocobalamin is a water-soluble vitamin that plays an essential role as an enzyme cofactor and antioxidant, modulating nucleic acid metabolism and gene regulation. It is widely used as a therapeutic agent and supplement, because of its efficacy and stability. In this report, we demonstrate that although Cobl can be an excellent antioxidant, exposure to high levels of HOCl can overcome the beneficial effects of Cobl and generate proinflammatory reaction products. Our rapid kinetic, HPLC, and mass spectrometric analyses showed that HOCl can mediate corrin ring destruction and liberate cyanogen chloride (CNCl) through a mechanism that initially involves α-axial ligand replacement in Cobl to form a chlorinated derivative, hydrolysis, and cleavage of the phosphonucleotide moiety. Additionally, it can liberate free Co, which can perpetuate metal-ion-induced oxidant stress. Taken together, these results are the first report of the generation of toxic molecular products through the interaction of Cobl with HOCl.

Biochemistry of B12-cofactors in human metabolism

Vitamin B12, the "antipernicious anaemia factor", is a crystallisable cobalt-complex, which belongs to a group of unique "complete" corrinoids, named cobalamins (Cbl). In humans, instead of the "vitamin", two organometallic B12-forms are coenzymes in two metabolically important enzymes: Methyl-cobalamin, the cofactor of methionine synthase, and coenzyme B12 (adenosyl-cobalamin), the cofactor of methylmalonyl-CoA mutase. The cytoplasmatic methionine synthase catalyzes the transfer of a methyl group from N-methyl-tetrahydrofolate to homocysteine to yield methionine and to liberate tetrahydrofolate. In the mitochondrial methylmalonyl-CoA mutase a radical process transforms methylmalonyl-CoA (a remains e.g. from uneven numbered fatty acids) into succinyl-CoA, for further metabolic use. In addition, in the human mitochondria an adenosyl-transferase incorporates the organometallic group of coenzyme B12. In all these enzymes, the bound B12-derivatives engage (or are formed) in exceptional organometallic enzymatic reactions. This chapter recapitulates the physiological chemistry of vitamin B12, relevant in the context of the metabolic transformation of B12-derivatives into the relevant coenzyme forms and their use in B12-dependent enzymes.

Cobalamin deficiency

Cobalamin (Cbl, vitamin B12) consists of a corrinoid structure with cobalt in the centre of the molecule. Neither humans nor animals are able to synthesize this vitamin. Foods of animal source are the only natural source of cobalamin in human diet. There are only two enzymatic reactions in mammalian cells that require cobalamin as cofactor. Methylcobolamin is a cofactor for methionine synthase. The enzyme methylmalonyl-CoA-mutase requires adenosylcobalamin as a cofactor. Therefore, serum concentrations of homocysteine (tHcy) and methylmalonic acid (MMA) will increase in cobalamin deficiency. The cobalamin absorption from diet is a complex process that involves different proteins: haptocorrin, intrinsic factor and transcobalamin (TC). Cobalamin that is bound to TC is called holotranscobalamin (holoTC) which is the metabolically active vitamin B12 fraction. HoloTC consists 6 and 20% of total cobalamin whereas 80% of total serum cobalamin is bound to another binding protein, haptocorrin. Cobalamin deficiency is common worldwide. Cobalamin malabsorption is common in elderly subjects which might explain low vitamin status. Subjects who ingest low amount of cobalamin like vegetarians develop vitamin deficiency. No single parameter can be used to diagnose cobalamin deficiency. Total serum cobalamin is neither sensitive nor it is specific for cobalamin deficiency. This might explain why many deficient subjects would be overlooked by utilizing total cobalamin as status marker. Concentration of holotranscobalamin (holoTC) in serum is an earlier marker that becomes decreased before total serum cobalamin. Concentrations of MMA and tHcy increase in blood of cobalamin deficient subjects. Despite limitations of these markers in patients with renal dysfunction, concentrations of MMA and tHcy are useful functional markers of cobalamin status. The combined use of holoTC and MMA assays may better indicate cobalamin status than either of them. Because Cbl deficiency is a risk factor for neurodegenerative diseases an early diagnosis of a low B12 status is required which should be followed by an effective treatment in order to prevent irreversible damages.

Effect of pH on the interaction of vitamin B12 with bovine serum albumin by spectroscopic approaches

The interaction mechanism between vitamin B12 (B12, cyanocobalamin) and bovine serum albumin (BSA) has been investigated by fluorescence, synchronous fluorescence, ultraviolet-vis (UV) absorbance, and three-dimensional fluorescence. The intrinsic fluorescence of BSA was strongly quenched by the addition of B12 in different pH buffer solutions (pH 2.5, 3.5, 5.0, 7.4, and 9.0) and spectroscopic observations are mainly rationalized in terms of a static quenching process at lower concentration of B12 (C(B12)/C(BSA)<5) and a combined quenching process at higher concentration of B12 (C(B12)/C(BSA)>5). The structural characteristics of B12 and BSA were probed, and their binding affinities were determined under different pH conditions. The results indicated that the binding abilities of B12 to BSA in the acidic and basic pH regions (pH 2.5, 3.5, 5.0, and 9.0) were lower than that at simulating physiological condition (pH 7.4). In addition, the efficiency of energy transfer from tryptophan fluorescence to B12 was found to depend on the binding distance r between the donor and acceptor calculated using Förster's theory. The effect of B12 on the conformation of BSA was analyzed using UV, synchronous fluorescence and three-dimensional fluorescence under different pH conditions. These results showed that the binding of B12 to BSA causes apparent change in the secondary and tertiary structures of BSA.

Investigating the intermediates in the reaction of ribonucleoside triphosphate reductase from Lactobacillus leichmannii: An application of HF EPR-RFQ technology

In this investigation high-frequency electron paramagnetic resonance spectroscopy (HFEPR) in conjunction with innovative rapid freeze-quench (RFQ) technology is employed to study the exchange-coupled thiyl radical-cob(II)alamin system in ribonucleotide reductase from a prokaryote Lactobacillus leichmannii. The size of the exchange coupling (Jex) and the values of the thiyl radical g tensor are refined, while confirming the previously determined (Gerfen et al. (1996) [20]) distance between the paramagnets. Conclusions relevant to ribonucleotide reductase catalysis and the architecture of the active site are presented. A key part of this work has been the development of a unique RFQ apparatus for the preparation of millisecond quench time RFQ samples which can be packed into small (0.5 mm ID) sample tubes used for CW and pulsed HFEPR--lack of this ability has heretofore precluded such studies. The technology is compatible with a broad range of spectroscopic techniques and can be readily adopted by other laboratories.

Age-related lysosomal dysfunction: an unrecognized roadblock for cobalamin trafficking?

Vitamin-B(12) is a generic term for corrinoid compounds that exhibit the biological activity of cyanocobalamin and are collectively referred to as cobalamins. Methylcobalamin and 5-deoxyadenosylcobalamin are the active cobalamins in human metabolism. Cobalamin plays a crucial role in the maintenance of homocysteine and methylmalonyl-CoA homeostasis and is required for erythrocyte formation and DNA synthesis. Data from human and animal studies indicate that cobalamin deficiency impairs neuronal function; a process that is thought to contribute to age-related cognitive decline and dementia. Cobalamin deficiency also results in dysfunction of the peripheral nervous system; among other disorders. Although there is a detailed understanding of the biochemical pathways that are perturbed in cobalamin deficiency, the mechanisms underlying age-related dyshomeostasis in such pathways remain to be addressed. Because cobalamin utilization is dependent on its efficient transit through lysosomes, and mounting evidence indicates that lysosomal function deteriorates in aging long-lived post-mitotic cells such as neurons, in the present article we review published data that supports the proposition that impaired lysosomal processing of cobalamin may play a significant role in age-related (neuro) degenerative diseases.

Determination Co2+ in vitamin B12 based on enhancement of 2-(4-substituted-phenyl)-4,5-di(2-furyl) imidazole and H2O2 chemiluminescence reaction

In this paper, three kinds of imidazole derivatives, 2-(4-methylphenyl)-4,5-di(2-furyl) imidazole (MDFI), 2-(4-nitrophenyl)-4,5-di(2-furyl) imidazole (NDFI), and 2-(4-tert-butylphenyl)-4,5-di(2-furyl) imidazole (t-BDFI) were synthesized. In an alkaline medium, the chemiluminescence (CL) reaction of imidazole derivatives with H(2)O(2) has been investigated. It was also found that MDFI/H(2)O(2) and t-BDFI/H(2)O(2) systems gave strong CL. When Co(2+) was added into the two CL systems, the CL intensity was remarkably enhanced. In the optimum conditions, the CL intensity is linearly related to the logarithm of concentration of Co(2+). The linear ranges are 5×10(-9)-2.5×10(-7) mol/L for MDFI/H(2)O(2) system and 5×10(-9)-2.5×10(-7) mol/L for t-BDFI/H(2)O(2) system, and the corresponding detection limits are 1.2×10(-9) mol/L and 1.1×10(-9) mol/L, respectively. The method was applied to the determination of Co(2+) in vitamin B(12) injection. Furthermore, the CL mechanism was also discussed.

The Thermoanaerobacter glycobiome reveals mechanisms of pentose and hexose co-utilization in bacteria

Thermoanaerobic bacteria are of interest in cellulosic-biofuel production, due to their simultaneous pentose and hexose utilization (co-utilization) and thermophilic nature. In this study, we experimentally reconstructed the structure and dynamics of the first genome-wide carbon utilization network of thermoanaerobes. The network uncovers numerous novel pathways and identifies previously unrecognized but crucial pathway interactions and the associated key junctions. First, glucose, xylose, fructose, and cellobiose catabolism are each featured in distinct functional modules; the transport systems of hexose and pentose are apparently both regulated by transcriptional antiterminators of the BglG family, which is consistent with pentose and hexose co-utilization. Second, glucose and xylose modules cooperate in that the activity of the former promotes the activity of the latter via activating xylose transport and catabolism, while xylose delays cell lysis by sustaining coenzyme and ion metabolism. Third, the vitamin B₁₂ pathway appears to promote ethanologenesis through ethanolamine and 1, 2-propanediol, while the arginine deiminase pathway probably contributes to cell survival in stationary phase. Moreover, by experimentally validating the distinct yet collaborative nature of glucose and xylose catabolism, we demonstrated that these novel network-derived features can be rationally exploited for product-yield enhancement via optimized timing and balanced loading of the carbon supply in a substrate-specific manner. Thus, this thermoanaerobic glycobiome reveals novel genetic features in carbon catabolism that may have immediate industrial implications and provides novel strategies and targets for fermentation and genome engineering.

Renewable liquid fuels derived from lignocellulosic biomass could alleviate global energy shortage and climate change. Cellulose and hemicellulose are the main components of lignocellulosic biomass. Therefore, the ability to simultaneously utilize pentose and hexose (i.e., co-utilization) has been a crucial challenge for industrial microbes producing lignocellulosic biofuels. Certain thermoanaerobic bacteria demonstrate this unusual talent, but the genetic foundation and molecular mechanism of this process remain unknown. In this study, we reconstructed the structure and dynamics of the first genome-wide carbon utilization network of thermoanaerobes. This transcriptome-based co-expression network reveals that glucose, xylose, fructose, and cellobiose catabolism are each featured on distinct functional modules. Furthermore, the dynamics of the network suggests a distinct yet collaborative nature between glucose and xylose catabolism. In addition, we experimentally demonstrated that these novel network-derived features can be rationally exploited for product-yield enhancement via optimized timing and balanced loading of the carbon supply in a substrate-specific manner. Thus, the newly discovered modular and precisely regulated network elucidates unique features of thermoanaerobic glycobiomes and reveals novel perturbation strategies and targets for the enhanced thermophilic production of lignocellulosic biofuels.

[Comparison study on adsorption of middle molecular substances with multiwalled carbon nanotubes and activated carbon]

In recent years, multi-walled carbon nanotubes (MWCTs) are very favorable to the adsorption of middle molecular substances in the hemoperfusion because of their multiporous structure, large surface area and high reactivity, which are beneficial to the excellent absorption properties. The purpose of this study was to study the MWCTs on the adsorption capacity of the middle molecular substances. Vitamin B12 (VB12) was selected as a model of the middle molecular substances. The morphologies of MWCTs and activated carbon from commercial "carbon kidney" were observed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The adsorption behavior of VB12 was compared to each other with UV-visible absorption spectra. The MWCTs formed a sophistaicate gap structure, and compared to the activated carbon, MWCTs had a larger surface area. By Langmuir equation and Freundlich equation fitting analysis, VB12 adsorption on MWCTs is fit for multi-molecular layer adsorption, and the adsorption type of activated carbon is more inclined to the model corresponding to Langmuir monolayer adsorption. The adsorption rate of MWCTs is faster than that of the activated carbon and the adsorption capacity is greater, which could be expected to become the new adsorbent in the hemoperfusion.

Synthesis and application of a new thiazolylazo reagent for cloud point extraction and determination of cobalt in pharmaceutical preparations

The synthesis and characterization of the reagent 2-(5-bromothiazolylazo)-4-chlorophenol and its application in the development of a preconcentration procedure for cobalt determination using flame atomic absorption spectrometry after cloud point extraction is presented. This procedure is based on cobalt complexing and entrapment of the metal chelates into micelles of a surfactant-rich phase of Triton X-114. The preconcentration procedure was optimized by using a response surface methodology through the application of the Box-Behnken matrix. Under optimum conditions, the procedure determined the presence of cobalt with an LOD of 2.8 microg/L and LOQ of 9.3 microg/L. The enrichment factor obtained was 25. The precision was evaluated as the RSD, which was 5.5% for 10 microg/L cobalt and 6.9% for 30 microg/L. The accuracy of the procedure was assessed by comparing the results with those found using inductively coupled plasma-optical emission spectrometry. After validation, the procedure was applied to the determination of cobalt in pharmaceutical preparation samples containing cobalamin (vitamin B12).

Determination of vitamin B12 in fortified bovine milk-based infant formula powder, fortified soya-based infant formula powder, vitamin premix, and dietary supplements by surface plasmon resonance: collaborative study

A collaborative study was conducted on an inhibition-based protein-binding assay using the Biacore Q biosensor instrument and the Biacore Qflex Kit Vitamin B12 PI. The samples studied included infant formula, cereals, premixes, vitamin tablets, dietary supplements, and baby food. The collaborative study, which involved 11 laboratories, demonstrated that the assay showed an RSDr of 1.59-27.8 and HorRat values for reproducibility of 0.34-1.89 in samples with levels ranging from ppm to ppb. The assay studied is a label-free protein binding-based assay that uses the principle of surface plasmon resonance (SPR) to measure the interaction between vitamin B12 and a specific binding protein. A Biacore Q biosensor uses this principle to detect binding directly at the surface of a sensor chip with a hydrophilic gold-dextran surface. The instrument passes a mixture of prepared sample extract and binding protein solution across a covalently immobilized vitamin B12 chip surface, and the response is given as free-binding protein as the mixture binds to the immobilized surface. This technique uses the specificity and robustness of the protein-ligand interaction to allow minimal sample preparation and a wide range of matrixes to be analyzed rapidly. The reagents and accessories needed to perform this assay are provided as the ready-to-use format "Qflex Kit Vitamin B12 PI." The method is intended for routine use in the quantitative determination of vitamin B12 (as cyanocobalamin) in a wide range of food products, dietary vitamin supplements, and multivitamin premixes.

A new trick (hydroxyl radical generation) for an old vitamin (B12)

Photolysis of hydroxocobalamin in the presence of plasmid DNA (pBR322) results in DNA cleavage. Temporal control of hydroxyl radical production and DNA strand scission by hydroxocobalamin was demonstrated using a 2-deoxyribose assay and a plasmid relaxation assay, respectively. The light-driven hydroxocobalamin-mediated catalytic formation of hydroxyl radicals was demonstrated using radical scavenging studies of DNA cleavage and via recycling of a hydroxocobalamin-resin conjugate several times without loss of efficacy.

Chemical pathology of homocysteine. V. Thioretinamide, thioretinaco, and cystathionine synthase function in degenerative diseases

Hyperhomocysteinemia was first associated with degenerative disease by observation of accelerated arteriosclerosis in children with inherited disorders of cystathionine synthase, methionine synthase, and methylene tetrohydrofolate reductase. The metabolic blockade of sulfate synthesis from homocysteine thiolactone in malignant cells is ascribed to a deficiency of a chemopreventive derivative of homocysteine thiolactone that occurs in normal cells. Its chemical structure was elucidated by the organic synthesis of thioretinamide from retinoic acid and homocysteine thiolactone. Oxidation of the sulfur atom of homocysteine is inhibited in scorbutic guinea pigs, demonstrating ascorbate function in sulfate synthesis from homocysteine. Studies of homocysteine metabolism in protein energy malnutrition led to the conclusion that the biosynthesis of thioretinamide from the retinol of transthyretin is catalyzed by dehydroascorbate and superoxide generated from the heme oxygenase group of cystathionine synthase. Newly synthesized thioretinamide is complexed with cobalamin to form thioretinaco, which is activated by ozone and oxygen to function as the active site of oxidative phosphorylation. In accordance with the trophoblastic theory of cancer, pancreatic enzymes are believed to be oncolytic because they hydrolyze the homocysteinylated proteins, nucleic acids and glycosaminoglycans of malignant tissues. The clonal selection of malignant cells that are deficient in the heme oxygenase function of cystathionine synthase produces cells dependent upon glycolysis for ATP synthesis, since they are deficient in synthesis of thioretinamide, thioretinaco and thioretinaco ozonide. The vulnerable plaque of arteriosclerosis originates from complexes of microbes with homocysteinylated lipoproteins, obstructing vasa vasorum narrowed by endothelial dysfunction, causing arterial ischemia, and intimal micro-abscesses. Degenerative diseases may be ameliorated by a proposed therapeutic protocol of thioretinamide with pancreatic enzymes.

A simple strategy for ¹³C, ¹H labeling at the Ile-γ2 methyl position in highly deuterated proteins

A straightforward approach for the production of highly deuterated proteins labeled with ¹³C and ¹H at Ile-γ2 methyl positions is described. The utility of the methodology is illustrated with an application involving the half proteasome (360 kDa). High quality 2D Ile ¹³C(γ)²,¹H(γ)² HMQC data sets, exploiting the methyl-TROSY principle, are recorded with excellent sensitivity and resolution, that compare favorably with Ile ¹³C(δ)¹,¹H(δ)¹ spectra. This labeling scheme adds to a growing list of different approaches that are significantly impacting the utility of solution NMR spectroscopy in studies of supra-molecular systems.

Purification, identification, and characterization of methylcobalamin from Spirulina platensis

The present study reports methylcobalamin in Spirulina platensis using high-performance liquid chromatography (HPLC), thin-layer chromatography (TLC), microbiological assay, chemiluminescence assay, liquid chromatography-mass spectrometry (LC-MS), and tandem mass spectrometry (MS/MS). Extraction of vitamin B12 from S. platensis was carried out without using cyanide. Partial purification was achieved using Amberlite XAD-2 followed by elution with 80% (v/v) methanol. Activated charcoal facilitated removal of impurities in S. platensis extract and in further purification of vitamin B12. The purified fraction was identified to contain methylcobalamin as analyzed by HPLC and TLC. Authenticity of methylcobalamin was further confirmed by LC-MS and MS/MS. Quantitation of methylcobalamin in a test sample of S. platensis biomass was performed using microbiological assay and chemiluminescence assay and was found to be 38.5±2 and 35.7±2 μg/100 g of dry biomass, respectively.

Crystal structures of ethanolamine ammonia-lyase complexed with coenzyme B12 analogs and substrates

N-terminal truncation of the Escherichia coli ethanolamine ammonia-lyase beta-subunit does not affect the catalytic properties of the enzyme (Akita, K., Hieda, N., Baba, N., Kawaguchi, S., Sakamoto, H., Nakanishi, Y., Yamanishi, M., Mori, K., and Toraya, T. (2010) J. Biochem. 147, 83-93). The binary complex of the truncated enzyme with cyanocobalamin and the ternary complex with cyanocobalamin or adeninylpentylcobalamin and substrates were crystallized, and their x-ray structures were analyzed. The enzyme exists as a trimer of the (alphabeta)(2) dimer. The active site is in the (beta/alpha)(8) barrel of the alpha-subunit; the beta-subunit covers the lower part of the cobalamin that is bound in the interface of the alpha- and beta-subunits. The structure complexed with adeninylpentylcobalamin revealed the presence of an adenine ring-binding pocket in the enzyme that accommodates the adenine moiety through a hydrogen bond network. The substrate is bound by six hydrogen bonds with active-site residues. Argalpha(160) contributes to substrate binding most likely by hydrogen bonding with the O1 atom. The modeling study implies that marked angular strains and tensile forces induced by tight enzyme-coenzyme interactions are responsible for breaking the coenzyme Co-C bond. The coenzyme adenosyl radical in the productive conformation was modeled by superimposing its adenine ring on the adenine ring-binding site followed by ribosyl rotation around the N-glycosidic bond. A major structural change upon substrate binding was not observed with this particular enzyme. Glualpha(287), one of the substrate-binding residues, has a direct contact with the ribose group of the modeled adenosylcobalamin, which may contribute to the substrate-induced additional labilization of the Co-C bond.

Effect of vitamin B12 pulse addition on the performance of cobalt deprived anaerobic granular sludge bioreactors

The effect of a pulse addition of vitamin B(12) as cobalt source to restore the performance of cobalt depleted methanol-fed bioreactors was investigated. One upflow anaerobic sludge bed (UASB) reactor was supplied with a pulse of vitamin B(12), and its operation was compared to that of another cobalt depleted UASB reactor to which a pulse of CoCl(2) was given. The addition of cobalt in the form of CoCl(2) supplies enough cobalt to restore methanogenesis and maintain full methanol degradation coupled to methane production during more than 35 days after the CoCl(2) pulse. Similar to CoCl(2), pulse addition of vitamin B(12) supplies enough cobalt to maintain full methanol degradation during more than 35 days after the pulse. However, the specific methanogenic activities (SMAs) of the sludge in the vitamin B(12) supplied reactor were around 3 times higher than the SMA of the sludge from the CoCl(2) supplied reactor at the same sampling times. An appropriate dosing strategy (repeated pulse dosing) combined with the choice of vitamin B(12) as the cobalt species is suggested as a promising dosing strategy for methanol-fed anaerobic bioreactors limited by the micronutrient cobalt.

New facile method to measure cyanide in blood

Cyanide, a well-known toxic substance that could be used as a weapon of mass destruction, is likely responsible for a substantial percentage of smoke inhalation deaths. The vitamin B(12) precursor cobinamide binds cyanide with high affinity, changing color and, correspondingly, its spectrophotometric spectrum in the ultraviolet/visible light range. Based on these spectral changes, we developed a new facile method to measure cyanide in blood using cobinamide. The limit of detection was 0.25 nmol, while the limit of quantitation was approximately 0.5 nmol. The method was reliable, requires minimal equipment, and correlated well with a previously established method. Moreover, we adapted it for rapid qualitative assessment of cyanide concentration, which could be used in the field to identify cyanide-poisoned subjects for immediate treatment.

Thermolability of mutant MMACHC protein in the vitamin B12-responsive cblC disorder

Methylmalonic aciduria and homocystinuria, cblC type, is the most common inborn error of cellular vitamin B12 metabolism. We previously showed that the protein carrying the mutation responsible for late-onset cblC (MMACHC-R161Q), treatable with high dose OHCbl, is able to bind OHCbl with wild-type affinity, leaving undetermined the disease mechanism involved [Froese et al., Mechanism of responsiveness, Mol. Genet. Metab. (2009).]. To assess whether the mutation renders the protein unstable, we investigated the thermostability of the wild-type and mutant MMACHC proteins, either unbound or bound to different cobalamins (Cbl), using differential scanning fluorimetry. We found that MMACHC-wt and MMACHC-R161Q are both very thermolabile proteins in their apo forms, with melting temperatures (T(m)) of 39.3+/-1.0 and 37.1+/-0.7 degrees C, respectively; a difference confirmed by unfolding of MMACHC-R161Q but not MMACHC-wt by isothermal denaturation at 35 degrees C over 120 min. However, with the addition of OHCbl, MMACHC-wt becomes significantly stabilized (Delta T(m max)=8 degrees C, half-maximal effective ligand concentration, AC(50)=3 microM). We surveyed the effect of different cobalamins on the stabilization of the wild-type protein and found that AdoCbl was the most stabilizing, exerting a maximum increase in T(m) of approximately 16 degrees C, followed by MeCbl at approximately 13 degrees C, each evaluated at 50 microM cofactor. The other cobalamins stabilized in the order (CN)(2)Cbi>OHCbl>CNCbl. Interestingly, the AC(50)'s for AdoCbl, MeCbl, (CN)(2)Cbi and OHCbl were similar and ranged from 1-3 microM, which compares well with the K(d) of 6 microM for OHCbl [Froese et al., Mechanism of responsiveness, Mol. Genet. Metab. (2009).]. Unlike MMACHC-wt, the mutant protein MMACHC-R161Q is only moderately stabilized by OHCbl (Delta T(m max)=4 degrees C). The dose-response curve also shows a lower effectivity of OHCbl with respect to stabilization, with an AC(50) of 7 microM. MMACHC-R161Q showed the same order of stabilization as MMACHC-wt, but each cobalamin stabilized this mutant protein less than its wild-type counterpart. Additionally, MMACHC-R161Q had a higher AC(50) for each cobalamin form compared to MMACHC-wt. Finally, we show that MMACHC-R161Q is able to support the base-off transition for AdoCbl and CNCbl, indicating this mutant is not blocked in that respect. Taken together, our results suggest that protein stability, as well as propensity for ligand-induced stabilization, contributes to the disease mechanism in late-onset cblC disorder. Our results underscore the importance of cofactor stabilization of MMACHC and suggest that even small increases in the concentration of cobalamin complexed with MMACHC may have therapeutic benefit in children with the late-onset, vitamin responsive cblC disease.

Vitamin B12: unique metalorganic compounds and the most complex vitamins

The chemistry and biochemistry of the vitamin B(12) compounds (cobalamins, XCbl) are described, with particular emphasis on their structural aspects and their relationships with properties and function. A brief history of B(12), reveals how much the effort of chemists, biochemists and crystallographers have contributed in the past to understand the basic properties of this very complex vitamin. The properties of the two cobalamins, the two important B(12) cofactors Ado- and MeCbl are described, with particular emphasis on how the Co-C bond cleavage is involved in the enzymatic mechanisms. The main structural features of cobalamins are described, with particular reference to the axial fragment. The structure/property relationships in cobalamins are summarized. The recent studies on base-off/base-on equilibrium are emphasized for their relevance to the mode of binding of the cofactor to the protein scaffold. The absorption, transport and cellular uptake of cobalamins and the structure of the B(12) transport proteins, IF and TC, in mammals are reviewed. The B(12) transport in bacteria and the structure of the so far determined proteins are briefly described. The currently accepted mechanisms for the catalytic cycles of the AdoCbl and MeCbl enzymes are reported. The structure and function of B(12) enzymes, particularly the important mammalian enzymes methyltransferase (MetH) and methyl-malonyl-coenzyme A mutase (MMCM), are described and briefly discussed. Since fast proliferating cells require higher amount of vitamin B(12) than that required by normal cells, the study of B(12 )conjugates as targeting agents has recently gained importance. Bioconjugates have been studied as potential agents for delivering radioisotopes and NMR probes or as various cytotoxic agents towards cancer cells in humans and the most recent studies are described. Specifically, functionalized bioconjugates are used as "Trojan horses" to carry into the cell the appropriate antitumour or diagnostic label. Possible future developments of B(12) work are summarized.

Reconciling disparate models of the involvement of vinyl radicals in cobalamin-mediated dechlorination reactions

Inner-sphere (nonradical) and outer-sphere (radical-based) mechanisms have been suggested for cobalamin-mediated dechlorination of tetrachloroethylene (PCE) and trichloroethylene (TCE). In this study, the role of free vinyl radicals was investigated using deuterated radical traps: d(8)-isopropanol and d(8)-tetrahydrofuran. For both substrates, addition of trap resulted in production of deuterated dechlorination products, and higher concentrations of trap resulted in increased amounts of deuterated products. However, only a finite proportion of the products were trappable: 8% of the PCE-derived products and 86% of the TCE-derived products result from free radicals. The data show that the reaction does not proceed solely by either an inner-sphere or an outer-sphere mechanism and led to the hypothesis that caged radical intermediates were involved in the mechanism. The untrappable fraction of products are hypothesized to result from in-cage reactions. This hypothesis was investigated using d(5)-glycerol as a radical trap and viscogen. Although increased viscosity resulted in decreased formation of free-radical-derived products, consistent with the cage hypothesis, these data were inconclusive. The role of d(8)-isopropanol in enhancing the production of radicals in this system via an acetone ketyl radical chain mechanism was also investigated, and no evidence for such an effect was found.

Mass spectrometry of intact neutral macromolecules using intense non-resonant femtosecond laser vaporization with electrospray post-ionization

Intact, nonvolatile, biological macromolecules can be transferred directly from the solid state into the gas phase, in ambient air, for subsequent mass spectral analysis using non-resonant femtosecond (fs) laser desorption combined with electrospray ionization (ESI). Mass spectral measurements for neat samples, including a dipeptide, protoporphyrin IX and vitamin B12 adsorbed on a glass insulating surface, were obtained using an 800 nm, 70 fs laser with an intensity of 10(13) W cm(-2). No appreciable signal was detected when atmospheric matrix-assisted or neat (matrix-free) fs laser desorption was performed without ESI, indicating neutral desorption.

Preparation and characterization of novel gellan gum hydrogels suitable for modified drug release

Innovative hydrogels obtained by physical and chemical crosslinking of deacylated Gellan gum have been characterized in terms of water uptake, rheological properties and compressibility, and the behaviour of the tested materials, according to the type of the obtained network, is thoroughly discussed. The release from the various gels of loaded model molecules of different steric hindrance was also investigated and the trend of the release profiles has been related to the structures proposed for the physical and the chemical hydrogel.