Synthetic and Biological Studies on New Urea and Triazole Containing Cystobactamid Derivatives

Cystobactamids belong to the group of arene-based oligoamides that effectively inhibit bacterial type IIa topoisomerases. Cystobactamid 861-2 is the most active member of these antibiotics. Most amide bonds present in the cystobactamids link benzoic acids with anilines and it was found that some of these amide bonds undergo chemical and enzymatic hydrolysis, especially the one linking ring C with ring D. This work reports on the chemical synthesis and biological evaluation of thirteen new cystobactamids that still contain the methoxyaspartate hinge. However, we exchanged selected amide bonds either by the urea or the triazole groups and modified ring A in the latter case. While hydrolytic stability could be improved with these structural substitutes, the high antibacterial potency of cystobactamid 861-2 could only be preserved in selected cases. This includes derivatives, in which the urea group is positioned between rings A and B and where the triazole is found between rings C and D.

Unique Binding Specificities of Proteins toward Isomeric Asparagine-Linked Glycans

The glycan ligands recognized by Siglecs, influenza viruses, and galectins, as well as many plant lectins, are not well defined. To explore their binding to asparagine (Asn)-linked N-glycans, we synthesized a library of isomeric multiantennary N-glycans that vary in terminal non-reducing sialic acid, galactose, and N-acetylglucosamine residues, as well as core fucose. We identified specific recognition of N-glycans by several plant lectins, human galectins, influenza viruses, and Siglecs, and explored the influence of sialic acid linkages and branching of the N-glycans. These results show the unique recognition of complex-type N-glycans by a wide variety of glycan-binding proteins and their abilities to distinguish isomeric structures, which provides new insights into the biological roles of these proteins and the uses of lectins in biological applications to identify glycans.

A critical analysis of L-asparaginase activity quantification methods-colorimetric methods versus high-performance liquid chromatography

L-asparaginase or ASNase (L-asparagine aminohydrolase, E.C.3.5.1.1) is an enzyme clinically accepted as an antitumor agent to treat acute lymphoblastic leukemia (ALL) and lymphosarcoma through the depletion of L-asparagine (L-Asn) resulting in cytotoxicity to leukemic cells. ASNase is also important in the food industry, preventing acrylamide formation in processed foods. Several quantification techniques have been developed and used for the measurement of the ASNase activity, but standard pharmaceutical quality control methods were hardly reported, and in general, no official quality control guidelines were defined. To overcome this lack of information and to demonstrate the advantages and limitations, this work properly compares the traditional colorimetric methods (Nessler; L-aspartic acid β-hydroxamate (AHA); and indooxine) and the high-performance liquid chromatography (HPLC) method. A comparison of the methods using pure ASNase shows that the colorimetric methods both overestimate (Nessler) and underestimate (AHA and indooxine) the ASNase activity when compared to the values obtained with HPLC, considered the most precise method as this method monitors both substrate consumption and product formation, allowing for overall mass-balance. Correlation and critical analysis of each method relative to the HPLC method were carried out, resulting in a demonstration that it is crucial to select a proper method for the quantification of ASNase activity, allowing bioequivalence studies and individualized monitoring of different ASNase preparations. Graphical abstract ᅟ.

Nicrophorusamides A and B, Antibacterial Chlorinated Cyclic Peptides from a Gut Bacterium of the Carrion Beetle Nicrophorus concolor

Nicrophorusamides A and B (1 and 2) were discovered from a rare actinomycete, Microbacterium sp., which was isolated from the gut of the carrion beetle Nicrophorus concolor. The structures of the nicrophorusamides were established as new chlorinated cyclic hexapeptides bearing uncommon amino acid units mainly based on 1D and 2D NMR spectroscopic analysis. The absolute configurations of the amino acid residues 5-chloro-l-tryptophan, d-threo-β-hydroxyasparagine/d-asparagine, l-ornithine, l-allo-isoleucine, d-leucine, and d-valine were determined using Marfey's method and chemical derivatization with 2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl isothiocyanate followed by LC/MS analysis. Nicrophorusamide A (1) showed antibacterial activity against several Gram-positive bacteria.

Structure of human immunoproteasome with a reversible and noncompetitive inhibitor that selectively inhibits activated lymphocytes

Proteasome inhibitors benefit patients with multiple myeloma and B cell-dependent autoimmune disorders but exert toxicity from inhibition of proteasomes in other cells. Toxicity should be minimized by reversible inhibition of the immunoproteasome β5i subunit while sparing the constitutive β5c subunit. Here we report β5i-selective inhibition by asparagine-ethylenediamine (AsnEDA)-based compounds and present the high-resolution cryo-EM structural analysis of the human immunoproteasome. Despite inhibiting noncompetitively, an AsnEDA inhibitor binds the active site. Hydrophobic interactions are accompanied by hydrogen bonding with β5i and β6 subunits. The inhibitors are far more cytotoxic for myeloma and lymphoma cell lines than for hepatocarcinoma or non-activated lymphocytes. They block human B-cell proliferation and promote apoptotic cell death selectively in antibody-secreting B cells, and to a lesser extent in activated human T cells. Reversible, β5i-selective inhibitors may be useful for treatment of diseases involving activated or neoplastic B cells or activated T cells.

Long chain fatty acids alter the interactive binding of ligands to the two principal drug binding sites of human serum albumin

A wide variety of drugs bind to human serum albumin (HSA) at its two principal sites, namely site I and site II. A number of reports indicate that drug binding to these two binding sites are not completely independent, and that interactions between ligands of these two discrete sites can play a role. In this study, the effect of the binding of long-chain fatty acids on the interactive binding between dansyl-L-asparagine (DNSA; site I ligand) and ibuprofen (site II ligand) at pH6.5 was examined. Binding experiments showed that the binding of sodium oleate (Ole) to HSA induces conformational changes in the molecule, which, in turn, changes the individual binding of DNSA and ibuprofen, as well as the mode of interaction between these two ligands from a ‘competitive-like’ allosteric interaction in the case of the defatted HSA conformer to a ‘nearly independent’ binding in the case of non-defatted HSA conformer. Circular dichroism measurements indicated that ibuprofen and Ole are likely to modify the spatial orientation of DNSA at its binding site. Docking simulations suggest that the long-distance electric repulsion between DNSA and ibuprofen on defatted HSA contributes to a ‘competitive-like’ allosteric interaction, whereas extending the distance between ligands and/or increasing the flexibility or size of the DNSA binding site in fatted HSA evokes a change in the interaction mode to ‘nearly independent’ binding. The present findings provide further insights into the structural dynamics of HSA upon the binding of fatty acids, and its effects on drug binding and drug-drug interactions that occur on HSA.

Crystal structure of a mutant glycosylasparaginase shedding light on aspartylglycosaminuria-causing mechanism as well as on hydrolysis of non-chitobiose substrate

Glycosylasparaginase (GA) is an amidase that cleaves Asn-linked glycoproteins in lysosomes. Deficiency of this enzyme causes accumulation of glycoasparagines in lysosomes of cells, resulting in a genetic condition called aspartylglycosaminuria (AGU). To better understand the mechanism of a disease-causing mutation with a single residue change from a glycine to an aspartic acid, we generated a model mutant enzyme at the corresponding position (named G172D mutant). Here we report a 1.8Å resolution crystal structure of mature G172D mutant and analyzed the reason behind its low hydrolase activity. Comparison of mature G172D and wildtype GA models reveals that the presence of Asp 172 near the catalytic site affects substrate catabolism in mature G172D, making it less efficient in substrate processing. Also recent studies suggest that GA is capable of processing substrates that lack a chitobiose (Glycan, N-acetylchiobios, NAcGlc) moiety, by its exo-hydrolase activity. The mechanism for this type of catalysis is not yet clear. l-Aspartic acid β-hydroxamate (β-AHA) is a non-chitobiose substrate that is known to interact with GA. To study the underlying mechanism of non-chitobiose substrate processing, we built a GA-β-AHA complex structure by comparing to a previously published G172D mutant precursor in complex with a β-AHA molecule. A hydrolysis mechanism of β-AHA by GA is proposed based on this complex model.

Isolation of Coralmycins A and B, Potent Anti-Gram Negative Compounds from the Myxobacteria Corallococcus coralloides M23

Two new potent anti-Gram negative compounds, coralmycins A (1) and B (2), were isolated from cultures of the myxobacteria Corallococcus coralloides M23, together with another derivative (3) that was identified as the very recently reported cystobactamid 919-2. Their structures including the relative stereochemistry were elucidated by interpretation of spectroscopic, optical rotation, and CD data. The relative stereochemistry of 3 was revised to "S*R*" by NMR analysis. The antibacterial activity of 1 was most potent against Gram-negative pathogens, including Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumanii, and Klebsiella pneumoniae, with MICs of 0.1-4 μg/mL; these MICs were 4-10 and 40-100 times stronger than the antibacterial activities of 3 and 2, respectively. Thus, these data indicated that the β-methoxyasparagine unit and the hydroxy group of the benzoic acid unit were critical for antibacterial activity.

In Silico Investigation of Traditional Chinese Medicine for Potential Lead Compounds as SPG7 Inhibitors against Coronary Artery Disease

Coronary artery disease (CAD) is the most common cause of heart attack and the leading cause of mortality in the world. It is associated with mitochondrial dysfunction and increased level of reactive oxygen species production. According to the Ottawa Heart Genomics Study genome-wide association study, a recent research identified that Q688 spastic paraplegia 7 (SPG7) variant is associated with CAD as it bypasses the regulation of tyrosine phosphorylation of AFG3L2 and enhances the processing and maturation of SPG7 protein. This study aims to identify potential compounds isolated from Traditional Chinese Medicines (TCMs) as potential lead compounds for paraplegin (SPG7) inhibitors. For the crystallographic structure of paraplegin, the disordered disposition of key amino acids in the binding site was predicted using the PONDR-Fit protocol before virtual screening. The TCM compounds saussureamine C and 3-(2-carboxyphenyl)-4(3H)-quinazolinone, have potential binding affinities with stable H-bonds and hydrophobic contacts with key residues of paraplegin. A molecular dynamics simulation was performed to validate the stability of the interactions between each candidate and paraplegin under dynamic conditions. Hence, we propose these compounds as potential candidates as lead drug from the compounds isolated from TCM for further study in drug development process with paraplegin protein for coronary artery disease.

In silico investigation of potential pyruvate kinase M2 regulators from traditional Chinese medicine against cancers

A recent research in cancer research demonstrates that tumor-specific pyruvate kinase M2 (PKM2) plays an important role in chromosome segregation and mitosis progression of tumor cells. To improve the drug development of TCM compounds, we aim to identify potent TCM compounds as lead compounds of PKM2 regulators. PONDR-Fit protocol was utilized to predict the disordered disposition in the binding domain of PKM2 protein before virtual screening as the disordered structure in the protein may cause the side effect and downregulation of the possibility of ligand to bind with target protein. MD simulation was performed to validate the stability of interactions between PKM2 proteins and each ligand after virtual screening. The top TCM compounds, saussureamine C and precatorine, extracted from Lycium chinense Mill. and Abrus precatorius L., respectively, have higher binding affinities with target protein in docking simulation than control. They have stable H-bonds with residues A:Lys311 and some other residues in both chains of PKM2 protein. Hence, we propose the TCM compounds, saussureamine C and precatorine, as potential candidates as lead compounds for further study in drug development process with the PKM2 protein against cancer.

An assay for α 1,6-fucosyltransferase (FUT8) activity based on the HPLC separation of a reaction product with fluorescence detection

N-Glycans with an α-fucose unit linked to the 6-position of the innermost GlcNAc are widely distributed among the animal kingdom, from worms and insects to human. This α1,6-linked fucosyl residue, frequently referred to as a core fucose, is formed via the action of an α1,6-fucosyltransferase, the mammalian ortholog which is systematically called FUT8. In mammals, it is well known that the extent of core-fucosylation in cellular and secreted glycoproteins varies, e.g., according to differentiation and carcinogenesis of the cells. This chapter describes a method for the sensitive and quantitative assay of FUT8 activity using a fluorescence-labeled oligosaccharyl asparagine derivative as the glycosyl acceptor substrate.

Chronic alcohol consumption, abstinence and relapse: brain proton magnetic resonance spectroscopy studies in animals and humans

This chapter summarizes the peer-reviewed literature of proton magnetic resonance spectroscopy ((1)H MRS) studies on the effects of chronic and excessive alcohol consumption in both the animal and human brain. After a brief summary of the neuropathology of alcohol use disorders (AUD), we describe the primary brain metabolites measured by in vivo (1)H MRS. We then focus on published MRS studies of animal models of alcohol dependence and of treatment-seeking humans with AUD. We also summarize the scant MRS research on the much larger fraction of treatment-naïve individuals with AUD and the similarities and discrepancies relative to treatment-seekers. It is exceedingly apparent that premorbid and/or comorbid disorders/conditions, especially chronic smoking, among individuals with AUD contribute to the considerable variability in the pattern and magnitude of neurobiological and neurocognitive abnormalities in AUD. Therefore, we also review studies on the neurobiological consequences of the combined effects of chronic drinking and smoking in AUD. Finally, as AUD is characterized by a chronically relapsing/remitting course over lifetime and identification of those at greatest risk for relapse is important, we review (1)H MRS studies on brain spectroscopic measures that contribute to the prediction of relapse in AUD. We conclude with an overall assessment of the MRS research literature on brain alcohol effects, the role of animal and human studies in understanding the disease, and discuss the need of widely integrative MRS studies of cohorts that include individuals with comorbidies that are reflective of the general population with AUD.

[Effect of new derivatives of natural nitrogen-containing compounds on the level and metabolism of biogenic amines in brain structures and the life span of rats]

Effects of the analogs of transmitter amino acids on the level of biogenic amines and their metabolism in various structures of brain and on the life span of rats have been studied.

Stripe-like increase of rCBV beyond the visible border of glioblastomas: site of tumor infiltration growing after neurosurgery

We observed a stripe-like pattern of regional cerebral blood volume (rCBV) increase in a defined region adjacent to the contrast enhancement (CE) on MRI of glioblastomas (GBM) that we defined as the "striate sign" (SS). We hypothesized that the SS marks infiltration of GBM outside the CE volume transforming into future CE tumor in the follow-up. T2*-weighted dynamic susceptibility-weighted CE (DSC)-MRI, and T1 and T2-weighted images (WI) of 16 patients with GBM were retrospectively evaluated in a baseline MRI performed before neurosurgery. In seven of these patients we also performed a (1)H MR spectroscopic imaging ((1)H MRSI). The regions of interest (ROI) delineating the SS were defined on rCBV maps for each patient. ROIs were overlaid on follow-up T1-WI and T2-WI MRI performed 3, 6, and 9 months after neurosurgery. Size and maximum signal intensity (max SI) of de novo CE within the area of the SS were analyzed. Statistical analysis was performed with the Friedman test (P < 0.05). In 15/16 patients de novo CE completely covered the area of the SS within nine months. Normalized max SI of de-novo CE of the 3, 6, and 9-months follow-up MR examinations were significantly higher than in the baseline MRI (P < 0.001). Normalized choline was increased within the SS in all patients with de novo CE (n = 6). De-novo CE appeared within the SS in all patients (96% of all slices). This implies that the SS might indicate the site of future CE tumor, which represents the area of tumor growth after neurosurgery.

Effect of liposome characteristics and dose on the pharmacokinetics of liposomes coated with poly(amino acid)s

Long-circulating liposomes, such as PEG-liposomes, are frequently studied for drug delivery and diagnostic purposes. In our group, poly(amino acid) (PAA)-based coatings for long-circulating liposomes have been developed. These coatings provide liposomes with similar circulation times as compared to PEG-liposomes, but have the advantage of being enzymatically degradable. For PEG-liposomes it has been reported that circulation times are relatively independent of their physicochemical characteristics. In this study, the influence of factors such as PAA grafting density, cholesterol inclusion, surface charge, particle size, and lipid dose on the circulation kinetics of PAA-liposomes was evaluated after intravenous administration in rats. Prolonged circulation kinetics of PAA-liposomes can be maintained upon variation of liposome characteristics and the lipid dose given. However, the use of relatively high amounts of strongly charge-inducing lipids and a too large mean size is to be avoided. In conclusion, PAA-liposomes represent a versatile drug carrier system for a wide variety of applications.

The old is new again: asparagine oxidation in calcium-dependent antibiotic biosynthesis

Non-ribosomal peptides are built from both proteinogenic and non-proteinogenic amino acids. The latter resemble amino acids but contain modifications not found in proteins. The recent characterization of a non-heme Fe(2+) and alpha-ketoglutarate-dependent oxygenase that stereospecifically generates beta-hydroxyasparagine, an unnatural amino acid building block for the biosynthesis of calcium-dependent antibiotic, a lipopeptide antibiotic. This work improves our understanding of how these non-proteinogenic amino acids are synthesized.

Mechanistic and structural basis of stereospecific Cbeta-hydroxylation in calcium-dependent antibiotic, a daptomycin-type lipopeptide

Non-ribosomally synthesized lipopeptide antibiotics of the daptomycin type are known to contain unnatural beta-modified amino acids, which are essential for bioactivity. Here we present the biochemical and structural basis for the incorporation of 3-hydroxyasparagine at position 9 in the 11-residue acidic lipopeptide lactone calcium-dependent antibiotic (CDA). Direct hydroxylation of l-asparagine by AsnO, a non-heme Fe(2+)/alpha-ketoglutarate-dependent oxygenase encoded by the CDA biosynthesis gene cluster, was validated by Fmoc derivatization of the reaction product and LC/MS analysis. The 1.45, 1.92, and 1.66 A crystal structures of AsnO as apoprotein, Fe(2+) complex, and product complex, respectively, with (2S,3S)-3-hydroxyasparagine and succinate revealed the stereoselectivity and substrate specificity of AsnO. The comparison of native and product-complex structures of AsnO showed a lid-like region (residues F208-E223) that seals the active site upon substrate binding and shields it from sterically demanding peptide substrates. Accordingly, beta-hydroxylated asparagine is synthesized prior to its incorporation into the growing CDA peptide. The AsnO structure could serve as a template for engineering novel enzymes for the synthesis of beta-hydroxylated amino acids.

Synthesis and Analgesic Activities of Endomorphin-2 and Its Analogues

Endomorphin-2 (1; H-Tyr-Pro-Phe-Phe-NH2; EM2) and its novel cyclic asparagine (cycloAsn) analogues, H-Tyr-cAsn(CHPh)-Phe-Phe-NH2 (2) and H-Tyr-cAsn(CHMe2)-Phe-Phe-NH2 (3), were synthesized via liquid-phase synthesis. The structures of the products and intermediates were characterized by IR, 1H-NMR, MS, and HR-MS analyses. The antinociceptive activity of EM2 and its cyclic asparagine analogues were assessed in AcOH-induced abdominal constriction tests in mice with i.p. injection. The results show that the antinociceptive activities of EM2 and its cyclic asparagine analogue 2 were higher than those of aspirine and meperidine. Analogue 2 was observed to be a stronger analgesic with dose-dependence than EM2. The test mice did not show any tendency to be addicted while administrated of analogue 2 repeatedly and regularly.

Pharmacokinetics of poly(hydroxyethyl-l-asparagine)-coated liposomes is superior over that of PEG-coated liposomes at low lipid dose and upon repeated administration

'Stealth' liposomes with a poly(ethylene glycol) (PEG) coating are frequently studied for drug delivery and diagnostic purposes because of their prolonged blood circulation kinetics. However, several recent reports have demonstrated that PEG-liposomes are rapidly cleared at single low lipid doses (<1 micromol/kg) and upon repeated administration (time interval between the injections 5 days-4 weeks). Recently, poly(amino acid)-based stealth liposome coatings have been developed as alternative to the PEG-coating. In this study, the pharmacokinetic behavior of liposomes coated with the poly(amino acid) poly(hydroxyethyl-l-asparagine) (PHEA) was evaluated at low lipid doses and upon repeated administration in rats. Blood circulation times and hepatosplenic localization of PHEA-liposomes were assessed after intravenous injection. When administered at a dose of 0.25 micromol/kg or less, PHEA-liposomes showed significantly longer blood circulation times than PEG-liposomes. A second dose of PHEA-liposomes 1 week after the first injection was less rapidly cleared from the circulation than a second dose of PEG-liposomes. Although the mechanisms behind these observations are still not clear yet, the use of PHEA-liposomes appears beneficial when single low lipid doses and/or repeated dosing schedules are being applied.

Fusion-induced apoptosis contributes to thymocyte depletion by a pathogenic human immunodeficiency virus type 1 envelope in the human thymus

The mechanisms of CD4(+) T-cell depletion during human immunodeficiency virus type 1 (HIV-1) infection remain incompletely characterized. Of particular importance is how CD4(+) T cells are depleted within the lymphoid organs, including the lymph nodes and thymus. Herein we characterize the pathogenic mechanisms of an envelope from a rapid progressor (R3A Env) in the NL4-3 backbone (NL4-R3A) which is able to efficiently replicate and deplete CD4(+) thymocytes in the human fetal-thymus organ culture (HF-TOC). We demonstrate that uninterrupted replication is required for continual thymocyte depletion. During depletion, NL4-R3A induces an increase in thymocytes which uptake 7AAD, a marker of cell death, and which express active caspase-3, a marker of apoptosis. While 7AAD uptake is observed predominantly in uninfected thymocytes (p24(-)), active caspase-3 is expressed in both infected (p24(+)) and uninfected thymocytes (p24(-)). When added to HF-TOC with ongoing infection, the protease inhibitor saquinavir efficiently suppresses NL4-R3A replication. In contrast, the fusion inhibitors T20 and C34 allow for sustained HIV-1 production. Interestingly, T20 and C34 effectively prevent thymocyte depletion in spite of this sustained replication. Apoptosis of both p24(-) and p24(+) thymocytes appears to be envelope fusion dependent, as T20, but not saquinavir, is capable of reducing thymocyte apoptosis. Together, our data support a model whereby pathogenic envelope-dependent fusion contributes to thymocyte depletion in HIV-1-infected thymus, correlated with induction of apoptosis in both p24(+) and p24(-) thymocytes.

N-phosphonacetyl-L-isoasparagine a potent and specific inhibitor of Escherichia coli aspartate transcarbamoylase

The synthesis of a new inhibitor, N-phosphonacetyl-L-isoasparagine (PALI), of Escherichia coli aspartate transcarbamoylase (ATCase) is reported, as well as structural studies of the enzyme.PALI complex. PALI was synthesized in 7 steps from beta-benzyl L-aspartate. The KD of PALI was 2 microM. Kinetics and small-angle X-ray scattering experiments showed that PALI can induce the cooperative transition of ATCase from the T to the R state. The X-ray structure of the enzyme.PALI complex showed 22 hydrogen-bonding interactions between the enzyme and PALI. The kinetic characterization and crystal structure of the ATCase.PALI complex also provides detailed information regarding the importance of the alpha-carboxylate for the binding of the substrate aspartate.

1H NMR spectroscopy as a tool for determining the composition of poly(hydroxyethyl-L-asparagine)-coated liposomes

Liposomes coated with the poly(amino acid) poly(hydroxyethyl-L-asparagine) (PHEA) show long-circulation properties comparable to the frequently used PEG-liposomes. The pharmacokinetic characteristics of long-circulating liposomes are dependent on the density of the shielding polymer on the liposome surface. Therefore, it is necessary to know the exact composition of the liposomes including the amount of coating polymer present on the liposome surface. In this study, a 1H NMR method to establish the composition of liposomes coated with PHEA was developed and validated.

Highly regioselective synthesis of a 3-O-sulfonated arabino Lewisa asparagine building block suitable for glycopeptide synthesis

Using the stannylene method, the trisaccharide 2-acetamido-3-O-[6-O-benzyl-beta-D-galactopyranosyl]-4-O-[2,3,4-tri-O-benzyl-beta-D-arabinopyranosyl]-6-O-benzyl-2-deoxy-beta-D-glucopyranosyl azide was regioselectively sulfonated and, after reduction of the anomeric azide, coupled to Fmoc alpha-allyl aspartate. After Pd(0)-catalyzed deallylation, the sulfatyl Lewis(a) asparagine building block was obtained, suitable for solid-phase glycopeptide synthesis applying the fluoride labile PTMSEL linker system.

Beta-catenin in the fibroproliferative response to acute lung injury

Resolution of alveolar epithelial/capillary membrane damage after acute lung injury requires coordinated and effective tissue repair to reestablish a functional alveolar epithelial/capillary membrane barrier. We hypothesized that signaling pathways important in lung alveolar bud ontogeny are activated in the recovery and remodeling phases after profound oxidant stress lung injury in a murine model. To test this, we characterized the expression of noncanonical beta-catenin pathway proteins E-cadherin, integrin-linked kinase-1, and beta-catenin in mice undergoing normoxic recovery after exposure to butylated hydroxytoluene (BHT, ionol) and concomitant sublethal (75% O2) hyperoxia. Mice developed early acute lung injury with subsequent inflammation, collagen deposition, interstitial cellular proliferation, and lung architectural distortion. Reduced E-cadherin expression after 6 d of BHT and hyperoxia was accompanied by enhanced expression and nuclear localization of beta-catenin and increased integrin-linked kinase-1 expression during subsequent normoxic recovery. This resulted in increased expression of the cotranscriptional regulators TCF-1 and -3 and cyclin D1. Proliferation of murine lung epithelial-12 cells in vitro after 8 h of treatment with BHT quinone-methide and hyperoxia and 48 h of normoxic recovery was enhanced 2.7-fold compared with vehicle-treated control mice at the same time point. BHT/hyperoxia-exposed mice treated with the pan-caspase inhibitor z-ASP had increased acute lung injury and reduced survival despite the presence of TUNEL-positive cells, suggesting enhanced lung cell necrosis. Beta-catenin expression was reduced in z-ASP-co-treated lungs after BHT/hyperoxia. The noncanonical cadherin-beta-catenin axis is associated with fibroproliferative repair after BHT/hyperoxia exposure and may regulate epithelial proliferation and lung matrix remodeling and repair in response to lung injury.

Epidural spinal lipomatosis with acute onset of paraplegia in an HIV-positive patient treated with corticosteroids and protease inhibitor: case report

STUDY DESIGN

Case report.

OBJECTIVE

To report a case of HIV-related lipodystrophy with a rapid onset of symptoms from epidural lipomatosis in the wake of protease inhibitor and steroid treatment.

SUMMARY OF BACKGROUND DATA

Symptomatic spinal epidural lipomatosis is considered to be a rare condition usually presenting with slowly progressive cord or nerve root compression. Only 2 cases of spinal lipomatosis in HIV-related lipodystrophy have been reported.

METHODS

We describe the case of a 41-year-old male with HIV who received protease inhibitor medication and had neurologic deficits rapidly develop.

RESULTS

The patient had complete paraplegia develop within 12 hours from admission following a 1-day history of unsteady gait and a 3-day history of leg numbness. After diagnosis of epidural lipomatosis on magnetic resonance imaging, the patient underwent decompressive thoraco-laminectomy. He recovered well and was able to walk by postoperative day 4.

CONCLUSION

It is important to maintain an awareness for the possible association between HIV lipodystrophy and symptomatic epidural lipomatosis.

[Synthesis and toxicity of some new (sulfon-amidophenyl)-amide derivatives of N-(m-nitrobenzoil)-D,L-asparagine]

In order to obtain new compounds with potential antibacterial activity some new (sulfonamidophenyl)-amide derivatives of N-(m-nitrobenzoil)-D,L-asparagine have been synthesized. The compounds have been obtained by decyclization reaction of 2-(m-nitrophenyl)-4-(beta-amidomethyl)-delta2-oxazolinone with various sulfonamides. A toxicity study with determination of DL50 value has also been realized.

Resolution of N-linked oligosaccharides in glycoproteins based upon transglycosylation reaction by CE-TOF-MS

The resolution of asparagine-type oligosaccharides in glycoproteins was carried out by combination of the transglycosylation reaction and CE-TOF-MS. The oligosaccharides enzymatically transferred to a fluorescent acceptor (NDA-Asn-GlcNAc) with Endo-M. The resulting fluorescent-oligosaccharides were separated by CE and detected by TOF-MS. Disialo-Asn was successfully identified by the proposed procedure. Application to oligosaccharides in ovalbumin was also described in this communication.

Efficient Stereoselective Synthesis of γ-N-Glycosyl Asparagines by N-Glycosylation of Primary Amide Groups

The efficient and elegant synthesis of N-glycosides by N-glycosylation of asparagine-containing peptides is described. Glycosylation of primary amides with glycosyl N-phenyltrifluoroimidates in the presence of a catalytic amount of TMSOTf in nitromethane smoothly proceeded to provide the corresponding N-glycosyl amino acids in excellent yields. This coupling method was adaptable to the coupling of various glycosyl donors with amino acids and peptides.

Mechanisms of Acrylamide Formation

The formation of acrylamide (AA) from L-asparagine was studied in Maillard model systems under pyrolysis conditions. While the early Maillard intermediate N-glucosylasparagine generated approximately 2.4 mmol/mol AA, the Amadori compound was a less efficient precursor (0.1 mmol/mol). Reaction with alpha-dicarbonyls resulted in relatively low AA amounts (0.2-0.5 mmol/mol), suggesting that the Strecker aldehyde pathway is of limited relevance. Similarly, the Strecker alcohol 3-hydroxypropanamide generated low amounts of AA (0.2 mmol/mol). On the other hand, hydroxyacetone afforded more than 4 mmol/mol AA, indicating that alpha-hydroxycarbonyls are more efficient than alpha-dicarbonyls in transforming asparagine into AA. The experimental results are consistent with the reaction mechanism proposed, i.e. (i) Strecker-type degradation of the Schiff base leading to azomethine ylides, followed by (ii) beta-elimination of the decarboxylated Amadori compound to release AA. The functional group in beta-position on both sides of the nitrogen atom is crucial. Rearrangement of the azomethine ylide to the decarboxylated Amadori compound is the key step, which is favored if the carbonyl moiety contains a hydroxyl group in beta-position to the N-atom. The beta-elimination step in the amino acid moiety was demonstrated by reacting under pyrolysis conditions decarboxylated model Amadori compounds obtained by synthesis.

Uremia and insulin resistance: N-carbamoyl-asparagine decreases insulin-sensitive glucose uptake in rat adipocytes

BACKGROUND

In uremia, urea-derived cyanate reacts with amino groups irreversibly forming carbamoyl amino acids (C-AA) and carbamoyl proteins. Carbamoylated molecules can affect binding and trafficking and alter metabolic pathways. The C-AA role in insulin-sensitive glucose transport has not been explored and may contribute to insulin resistance in uremia.

METHODS

Insulin-stimulated glucose uptake by cultured rat adipocytes was measured using both 3-minute and 3-second assays. Adipocytes were incubated for 24 hours in medium containing 0.5 micromol/mL of 15 different C-AA. 125I-insulin binding studies were done. C-asparagine in plasma from 10 uremic patients on continuous ambulatory peritoneal dialysis (CAPD) was measured using high-performance liquid chromatography (HPLC).

RESULTS

Insulin-sensitive glucose uptake was reduced 34% by N-carbamoyl-l-asparagine, (N-C-Asn), in a dose-dependent manner with a half-maximally effective concentration of 0.15 micromol/mL. Fourteen other N-carbamoyl-amino acids as well as 0.5 micromol/mL of asparagine did not affect insulin sensitive glucose uptake. N-C-Asn, l-asparagine, and the other N-carbamoyl amino acids (0.5 micromol/mL) had no effect on basal glucose uptake. These data suggest that that N-C-Asn affects the insulin sensitive glucose transporter system. 125I-insulin binding studies demonstrated that N-C-Asn did not alter insulin binding. Glucose uptake measured using a 3-second assay showed that the glucose affinity of the transporter and glucose phosphorylation were not affected. In uremic patients managed by CAPD, the mean free N-C-Asn plasma level was 1.33 micromol/mL.

CONCLUSION

These data suggest that N-C-Asn concentration may contribute to the insulin resistance seen in uremia.

Massive accumulation of Man2GlcNAc2-Asn in nonneuronal tissues of glycosylasparaginase-deficient mice and its removal by enzyme replacement therapy

Aspartylglycosaminuria (AGU) is caused by deficient enzymatic activity of glycosylasparaginase (GA). The disease is characterized by accumulation of aspartylglucosamine (GlcNAc-Asn) and other glycoasparagines in tissues and body fluids of AGU patients and in an AGU mouse model. In the current study, we characterized a glycoasparagine carrying the tetrasaccharide moiety of alpha-D-Man-(1-->6)-beta-D-Man-(1-->4)-beta-D-GlcNAc-(1-->4)-beta-D-GlcNAc-(1-->N)-Asn (Man2GlcNAc2-Asn) in urine of an AGU patient and also in the tissues of the AGU mouse model. Quantitative analysis demonstrated a massive accumulation of the compound especially in nonneuronal tissues of the AGU mice, in which the levels of Man2GlcNAc2-Asn were typically 30-87% of those of GlcNAc-Asn. The highest level of Man2GlcNAc2-Asn was found in the liver, spleen, and heart tissues of the AGU mice, the respective amounts being 87%, 76%, and 57% of the GlcNAc-Asn levels. In the brain tissue of AGU mice the Man2GlcNAc2-Asn storage was only 9% of that of GlcNAc-Asn. In contrast to GlcNAc-Asn, the storage of Man2GlcNAc2-Asn markedly increased in the liver and spleen tissues of AGU mice as they grew older. Enzyme replacement therapy with glycosylasparaginase for 3.5 weeks reduced the amount of Man2GlcNAc2-Asn by 66-97% in nonneuronal tissues, but only by 13% in the brain tissue of the AGU mice. In conclusion, there is evidence for a role for storage of glycoasparagines other than aspartylglucosamine in the pathogenesis of AGU, and this possibility should be taken into consideration in the treatment of the disease.

Proton magnetic resonance spectroscopy in children with spastic diplegia

The objective of this prospective study was the application of proton magnetic resonance spectroscopy in children with spastic diplegia (SD) to determine the metabolite profile of SD children in the left basal ganglia, and to assess the relationship of this profile with motor and mental development. Patients with SD showed reduced ratios of N-acetylaspartate (NAA)/creatine (Cr), NAA/choline (Cho), NAA/myo-inositol (mI), Cho/NAA, Cho/Cr and Cho/mI in the basal ganglia compared to a well-matched control group. On the other hand, we noted increased Cr/NAA, Cr/Cho and mI/NAA ratios in the SD patients as compared with controls. NAA/mI ratios were positively correlated with the severity scale of cerebral palsy in SD children. There was also a significant correlation between Cr/NAA and mental retardation. Increased Cr/NAA, Cr/Cho and mI/NAA ratios in SD children may suggest the existence of the compensatory mechanisms in these patients. The NAA/mI ratio could be used as an additional marker of SD severity and Cr/NAA as a marker of the mental retardation.

Monohydroxamates of aspartic acid and glutamic acid exhibit antioxidant and angiotensin converting enzyme inhibitory activities

Two monohydroxamates of l-aspartic acid beta-hydroxamate (AAH) and l-glutamic acid gamma-hydroxamate (GAH) were used for testing antioxidant and angiotensin converting enzyme (ACE) inhibitory activities in comparison with those of asparagine and glutamine, respectively. The half-inhibition concentrations, IC(50), of scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) were 36 and 48 microM and against superoxide radicals were 18.99 and 6.33 mM, respectively, for AAH and GAH. However, no activities of asparagine and glutamine were found. AAH and GAH also exhibited activities against peroxynitrite-mediated dihydrorhodamine 123 oxidations and hydroxyl radical-mediated DNA damage. For ACE inhibitory activities, the IC(50) values were 4.92 and 6.56 mM, respectively, for AAH and GAH. The ACE hydrolyzed products on the TLC chromatogram also confirmed the inhibitory activities of the two amino acid hydroxamates on ACE. When 1.23 mM AAH was added, AAH showed competitive inhibitions against ACE, and the apparent inhibition constant (K(i)) was 2.20 mM.

4-methylthio 2-oxobutanoate transaminase: a specific target for antiproliferative agents

We have previously shown that the addition of 4-methylthio-2-oxobutanoate (MTOB) to cultures of methionine dependent neoplastic cells which lack endogenous MTOB restores their capacity to grow in the absence of exogenous methionine. Transition state inhibitors of the MTOB transaminase,responsible for the transamination of MTOB to methionine, had also been designed and selected for their capacity to inhibit the proliferation of methionine dependent neoplastic cells but not that of normal cells in culture. We now show that the transition state analogue : L-methionine ethyl esterpyridoxal(MEEP) with a structure corresponding to the oxo acid receptor covalently linked to pyridoxamine and the amine donor analogue: D-aspartate beta hydroxamate (D-AH) are efficient inhibitors of MTOB transaminase. [3H] MEEP uptake into transformed HeLa cells is similar to that in normal MRC5 cells, yet growth inhibition is seem in the transformed but not in the normal cells.MEEP irreversibly inhibits the activity of this enzyme when added to HeLa cells in culture but not that of the purified rat liver enzyme, probably due to pyridoxal phosphate already bound in the active site. On the contrary, D-AH is a noncompetitive reversible inhibitor of the purified rat liver enzyme in vitro and also inhibits intracellular HeLa MTOB transaminase. Furthermore, in HeLa cells both inhibitors induce DNA strand breaks typical of apoptotic cell death. These results provide evidence that MTOB transaminase is a potential target for antiproliferative agents which could selectively affect methionine-dependent neoplastic cells. The transition state intermediale : MEEP as an amine acceptor analogue was found to be 20 fold more effective than D-AH as the amine donor analogue in inducing apoptosis.

N -Acyl derivatives of Asn, new bacterial N -acyl D -amino acids with surfactant activity

New N-acyl D-amino acids were isolated from Bacillus pumilus IM 1801. Their structures were determined by chemical analysis and mass spectrometry. The lipid part was identified as a mixture of fatty acids with 11, 12, 13, 15, and 16 carbon atoms in the iso, anteiso or n configuration linked by an amide bond with a D-asparagine. They exhibited surfactant properties.

The apparent dependence of the diffusion coefficient of N-acetylaspartate upon magnetic field strength: evidence of an interaction with NMR methodology

An inverse relationship between applied magnetic field strength and the apparent diffusion coefficient (ADC) of several important brain metabolites including N-acetyl-l-aspartate (NAA), choline and creatine, measured in vivo using proton magnetic resonance spectroscopy (MRS), has been reported. In this investigation, using phantom studies of NAA at magnetic field strengths of 3 and 7 T, these observations have been verified under controlled MRS conditions in vitro, and the ADC of NAA has been found to vary inversely with magnetic field strength, decreasing at a rate of 2.5%/T at 20 degrees C. We have also assessed whether the effect is a function of a systemic bias in methodology, or if the effect is actually on the rate of molecular diffusion. This was done using an MRS-independent method for measurement of molecular diffusion in NAA phantoms at 0, 0.025 and 7 T applied magnetic field strengths. As a result, it has been demonstrated that the observed apparent magnetic field dependence of the ADC of NAA is a consequence of the NMR measurement and is apparently not a real effect on molecular diffusion.

Acylation is rate-limiting in glycosylasparaginase-catalyzed hydrolysis of N4-(4'-substituted phenyl)-L-asparagines

Glycosylasparaginase catalyzes the hydrolysis of the N-glycosylic bond between N-acetyl-D-glucosamine and L-asparagine in the catabolism of glycoproteins. The mechanism has been proposed to resemble that of serine proteases involving an acylation step where a nucleophilic attack by a catalytic Thr residue on the carbonyl carbon of the N-glycosylic bond gives rise to a covalent beta-aspartyl-enzyme intermediate, and a deacylation step to give the final products. The question posed in this study was: Is the acylation step the rate-limiting step in the hydrolysis reaction as in serine proteases? To answer this question a series of mostly new substituted anilides was synthesized and characterized, and their hydrolysis reactions catalyzed by glycosylasparaginase from human amniotic fluid were studied. Five N4-(4'-substituted phenyl)-L-asparagine compounds were synthesized and characterized: 4'-hydrogen, 4'-ethyl, 4'-bromo, 4'-nitro, and 4'-methoxy. Each of these anilides was a substrate for the enzyme. Hammett plots of the kinetic parameters showed that acylation is the rate-limiting step in the reaction and that upon binding the electron distribution of the substrate is perturbed toward the transition state. This is the first direct evidence that acylation is the rate-limiting step in the enzyme-catalyzed reaction. A Brønsted plot indicates a small, negative charge (-0.25) on the nitrogen atom of the leaving group anilines containing electron-withdrawing groups, and a small, positive charge (0.43) on the nitrogen atom of the leaving group anilines containing electron-donating groups. The free energy (incremental) change of binding (delta deltaGb) in the enzyme-substrate transition state complexes shows that substitution of a substituted phenyl group for the pyranosyl group in the natural substrate results in an overall loss of binding energy equivalent to a weak hydrogen bond, the magnitude of which is dependent on the substituent group. The data are consistent with a mechanism for glycosylasparaginase involving rapid formation of a tetrahedral structure upon substrate binding, and a rate-limiting breakdown of the tetrahedral structure to a covalent beta-aspartyl-enzyme intermediate that is dependent on the electronic properties of the substituent group and on the degree of protonation of the leaving group in the transition state by a general acid.

Bowl-shaped C(3)-symmetric receptor with concave phosphine oxide with a remarkable selectivity for asparagine derivatives

A bowl-shaped C(3)-symmetric receptor (1a) that has a phosphine oxide functionality in the interior of a "molecular bowl" shows remarkable selectivity for Asn derivatives. [structure: see text]

Identification of the L-aspartate transporter in Bacillus subtilis

YveA of Bacillus subtilis, a putative transporter of the amino acid/polyamine/organocation (APC) superfamily, is shown to mediate uptake of both L-aspartate and L-glutamate as well as having sensitivity to L-aspartate hydroxamate. This 14 TMS protein is the primary aspartate uptake system in B. subtilis and serves as the prototype for a new family within the APC superfamily.

Pentacopper(II) 12-metallacrown-4 complexes with alpha- and beta-aminohydroxamic acids in aqueous solution: a reinvestigation

A reinvestigation of the equilibria of (S)-alpha-alaninehydroxamic acid (alpha-Alaha) and (R)-aspartic-beta-hydroxamic acid (Asp-beta-ha) with copper(II) was performed in aqueous solution in order to clarify some contradictory literature reports regarding the stoichiometry of the polynuclear complexes formed. beta-Alaninehydroxamic acid (beta-Alaha, HL), for which the formation of a planar 12-metallacrown-4, [Cu(5)L(4)H(-4)](2+), was already reported, was also re-examined for comparison. Among the different techniques used (potentiometry, absorption spectrophotometry, spectropolarimetry and electrospray ionization mass spectrometry), ES data allowed to define unambiguously that all these three ligands form the same pentanuclear species. Therefore it can be concluded that in aqueous solution the hydroxamates of both alpha- and beta-amino acids form 12-metallacrown-4 complexes, and that the formers are less stable.

A novel synthesis of N-methyl asparagine, arginine, histidine, and tryptophan

[reaction: see text] N-Methyl amino acid residues in peptides modify several pharmacologically useful parameters, but synthesis of alkylated peptides is hampered by unavailability of N-methylated monomers. The syntheses of four N-methyl amino acids with basic side chains are presented. The side chains of these basic amino acids needed to be specially protected or constructed. This completes the set of 20 common L-amino acid N-methyl derivatives prepared via 5-oxazolidinone intermediates by our group.

Analytical validation of a microplate reader-based method for the therapeutic drug monitoring of L-asparaginase in human serum

The enzyme L-asparaginase (ASNASE), which hydrolyzes L-asparagine (L-Asn) to ammonia and L-aspartic acid (L-Asp), is commonly used for remission induction in acute lymphoblastic leukemia. To correlate ASNASE activity with L-Asn reduction in human serum, sensitive methods for the determination of ASNASE activity are required. Using L-aspartic beta-hydroxamate (AHA) as substrate we developed a sensitive plate reader-based method for the quantification of ASNASE derived from Escherichia coli and Erwinia chrysanthemi and of pegylated E. coli ASNASE in human serum. ASNASE hydrolyzed AHA to L-Asp and hydroxylamine, which was determined at 710 nm after condensation with 8-hydroxyquinoline and oxidation to indooxine. Measuring the indooxine formation allowed the detection of 2 x 10(-5)U ASNASE in 20 microl serum. Linearity was observed within 2.5-75 and 75-1,250 U/L with coefficients of correlation of r(2)>0.99. The coefficients of variation for intra- and interday variability for the three different ASNASE enzymes were 1.98 to 8.77 and 1.73 to 11.0%. The overall recovery was 101+/-9.92%. The coefficient of correlation for dilution linearity was determined as r(2)=0.986 for dilutions up to 1:20. This method combined with sensitive methods for the quantification of L-Asn will allow bioequivalence studies and individualized therapeutic drug monitoring of different ASNASE preparations.

Synthesis of alpha- and beta-glycosyl asparagine ethylene isosteres (C-glycosyl asparagines) via sugar acetylenes and Garner aldehyde coupling

A convergent approach has been developed for the synthesis of C-glycosyl amino acids in which the glycinyl moiety CH(NH2)CO2H is connected to the anomeric center of the sugar residue by a three carbon atom tether. Essentially, these compounds are isosteres of N-glycosyl asparagines in which the amide group has been replaced by an ethylene bridge. Following the coupling of alpha- or beta-D-linked lithium C-glycoside acetylides with N-Boc D-serinal acetonide (Garner aldehyde), the resulting adducts were transformed into the final N-Boc-C-glycosyl-alpha-aminopentanoic acids via reduction of the triple bond, deoxygenation, and oxidative cleavage of the oxazolidine ring. By this protocol, 12 C-glycosyl asparagines, six pairs of alpha- and beta-anomers, have been prepared incorporating the gluco, galacto, manno, and the corresponding 2-acetamido-2-deoxy residues.

A concise synthesis of beta-asparaginyladenylate

Stable analogues of acyladenylate intermediates, such as N-acylphosphoramidates, are useful probes of tRNA aminoacylation and enzyme mechanism, and have potential application as enzyme inhibitors. We now report a concise, "one-pot" synthesis of beta-asparaginyladenylate using a novel coupling protocol that yields the target N-acylphosphoramidate in three reactions from readily available precursors. This simple synthetic procedure may represent a general approach for the preparation of functionalized N-acylphosphoramidates from amides that do not undergo coupling under the conditions of existing literature protocols.

[Effect of a nibentan derivative LKhT53-91 on the heart electrophysiological parameters]

The compound LKhT5391 (a derivative of nibentan) affects the electrophysiological cardiac parameters to a lower extent than does nibentan. Administered in an effective antiarrhythmogenic dose (comparable with the effective dose of nibentan), LKhT5391 produces a less pronounced and shorter negative chronotropic action than does nibentan. The negative dromotropic effect of the compound studied is manifested only in the atrioventricular node, while not influencing conductivity through the atria and ventricles.

Design and synthesis of a series of (2R)-N(4)-hydroxy-2-(3-hydroxybenzyl)-N(1)- [(1S,2R)-2-hydroxy-2,3-dihydro-1H-inden-1-yl]butanediamide derivatives as potent, selective, and orally bioavailable aggrecanase inhibitors

A pharmacophore model of the P1' site, specific for aggrecanase, was defined using the specificity studies of the matrix metalloproteinases and the similar biological activity of aggrecanase and MMP-8. Incorporation of the side chain of a tyrosine residue into compound 1 as the P1' group provided modest selectivity for aggrecanase over MMP-1, -2, and -9. A cis-(1S)(2R)-amino-2-indanol scaffold was incorporated as a tyrosine mimic (P2') to conformationally constrain 2. Further optimization resulted in compound 11, a potent, selective, and orally bioavailable inhibitor of aggrecanase.

Glycosylasparaginase activity requires the alpha-carboxyl group, but not the alpha-amino group, on N(4)-(2-Acetamido-2-deoxy-beta-D-glucopyranosyl)-L-asparagine

Glycosylasparaginase catalyzes the hydrolysis of the N-glycosylic bond in N(4)-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-L-asparagine in the catabolism of N-linked oligosaccharides. A deficiency, or absence, of enzyme activity gives rise to aspartylglycosaminuria, the most common disorder of glycoprotein metabolism. The enzyme catalyzes the hydrolysis of a variety of asparagine and aspartyl compounds containing a free alpha-carboxyl group and a free alpha-amino group; computational studies suggest that the alpha-amino group actively participates in the catalytic mechanism. In order to study the importance of the alpha-carboxyl group and the alpha-amino group on the natural substrate to the reaction catalyzed by the enzyme, 14 analogues of the natural substrate were studied where the structure of the aspartyl group of the substrate was changed. The incremental binding energy (DeltaDeltaGb) for those analogues that were substrates was calculated. The results show that the alpha-amino group may be substituted with a group of comparable size, for the alpha-amino group contributes little, if any, to the transition state binding energy of the natural substrate. The alpha-amino group position acts as an "anchor" in the binding site for the substrate. On the other hand, the alpha-carboxyl group is necessary for enzyme activity; removal of the alpha-carboxyl group or changing it to an alpha-carboxamide group results in no hydrolysis reaction. Also, N-acetyl-D-glucosamine is not sufficient for binding to the active site for efficient hydrolysis by the enzyme. These results provide supporting evidence for a proposed intramolecular autoproteolytic activation reaction for the enzyme. However, the results raise a question as to an important role for the alpha-amino group in the catalytic mechanism as indicated in computational studies.

Interaction mechanism between indoxyl sulfate, a typical uremic toxin bound to site II, and ligands bound to site I of human serum albumin

PURPOSE

The study was performed for clarifying the mechanism of interaction between indoxyl sulfate (IS), a typical uremic toxin bound to site II, and site I-ligands when bound to human serum albumin (HSA). The effect of the N to B transition on the interactions was also examined.

METHODS

Quantitative investigation of the relations between ligands bound to HSA was performed by equilibrium dialysis, and the binding data were analyzed on the basis of a theoretical model for simultaneous binding of two ligands.

RESULTS

The high-affinity binding constants for the site I-ligands warfarin (WF) and dansyl-L-asparagine (DNSA) increased with increasing pH, whereas those for the site II-ligands IS and dansylsarcosine (DNSS) were hardly affected by pH. Mutual displacement experiments showed that even though IS binds to site II it influenced binding of DNSA at the azapropazone binding area in site I. By contrast, it is unlikely that IS affects the WF binding area of site I. Furthermore, pH-profiles showed that the interaction between IS and DNSA was very sensitive to the N to B transition: "competitive-like" strong allosteric regulation was observed for binding of the two ligands to the N conformer (pH 6.5), whereas in the B conformation (pH 8.5) binding of these molecules was nearly "independent".

CONCLUSIONS

The present data provide useful information for elucidating a potential mechanism of interaction between drugs and endogenous substances including uremic toxins.