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PubMed2006

Application of capillary zone electrophoresis with large-volume sample stacking to the sensitive determination of sulfonamides in meat and ground water.

A CZE method with UV-Vis detection has been established and validated for the determination of nine sulfonamides: sulfapyridine, sulfamethazine, sulfamerazine, sulfamether, sulfadiazine, sulfadimethoxine, sulfamethoxazole, sulfachlorpyridazine, and sulfamethizole. Optimum separation was obtained on a 64.5 cm x 75 microm bubble cell capillary using a buffer containing 45 mM sodium phosphate and 10% methanol at pH 7.3, with temperature and voltage of 27 degrees C and 25 kV, respectively. p-Aminobenzoic acid was used as an internal standard . Taking into account the lack of sensitivity of the UV-Vis detection, the application of an on-line preconcentration methodology, such as large-volume sample stacking with polarity switching has been proposed. This procedure combined with a solvent extraction/SPE method applied for off-line preconcentration and cleanup provides a significant improvement in the LODs, ranging from 2.59 to 22.95 mug/L for the studied compounds; the quantification of these residues being possible below the levels established by EU legislation in animal food products, such as meat. Satisfactory recoveries were also obtained in the analysis of these compounds in ground water.

Animals↗
PubMed2005

Expression of cytochromes P450 and glutathione S-transferases in human prostate, and the potential for activation of heterocyclic amine carcinogens via acetyl-coA-, PAPS- and ATP-dependent pathways.

Dietary factors appear to be involved in the high incidence of prostate cancer in "Westernized" countries, implicating dietary carcinogens such as heterocyclic amines (HAs) in the initiation of prostate carcinogenesis. We examined 24 human prostate samples with respect to their potential for activation and detoxification of HAs and the presence of DNA adducts formed in vivo. Cytochromes P450 1B1, 3A4 and 3A5 were expressed at low levels (<0.1-6.2 pmol/mg microsomal protein). N-Acetyltransferase (NAT) activities, using p-aminobenzoic acid (NAT1) and sulfamethazine (NAT2) as substrates, were <5-5,500 and <5-43 pmol/min/mg cytosolic protein, respectively. Glutathione S-transferases (GSTs) P1, M2 and M3 were expressed at 0.038-1.284, 0.005-0.126 and 0.010-0.270 microg/mg cytosolic protein, respectively; GSTM1 was expressed in all GSTM1-positive samples (0.012-0.291 microg/mg cytosolic protein); and GSTA1 was expressed at low levels (<0.01-0.11 microg/mg cytosolic protein). Binding of N-hydroxy-PhIP to DNA in vitro occurred primarily by an AcCoA-dependent process (<1-54 pmol/mg/DNA), PAPS- and ATP-dependent binding being <1-7 pmol/mg DNA. In vivo, putative PhIP- or 4-aminobiphenyl-DNA adducts were found in 4 samples (0.4-0.8 adducts/10(8) bases); putative hydrophobic adducts were found in 6 samples (8-64 adducts/10(8) bases). Thus, the prostate appears to have low potential for N-hydroxylation of HAs but greater potential for activation of N-hydroxy HAs to genotoxic N-acetoxy esters. The prostate has potential for GSTP1-dependent detoxification of ATP-activated N-hydroxy-PhIP but little potential for detoxification of N-acetoxy-PhIP by GSTA1. However, there were no significant correlations between expression/activities and DNA adducts formed in vitro or in vivo, DNA adducts in vivo possibly reflecting carcinogen exposure.

Acetyl Coenzyme A↗
PubMedDate not supplied

The bentiromide test for pancreatic exocrine insufficiency.

The bentiromide test, a test of pancreatic exocrine function, has recently been approved for clinical use by the Food and Drug Administration. The test has been studied in adult patients with chronic pancreatic disease and in children with cystic fibrosis. The 500-mg dose and 6-hour urine collection period appear optimal for separating patients with chronic pancreatic disease from control subjects. Side effects with the 500-mg dose are virtually nonexistent. This simply performed outpatient test of chymotrypsin function appears to be an excellent means of confirming the diagnosis of pancreatic exocrine insufficiency.

4-Aminobenzoic Acid↗
PubMed1977

Convective diffusional analysis for drug transport through a tubular polymeric membrane.

The transport of three p-aminobenzoate esters (ethyl, butyl, and hexyl) through a tubular dimethyl polysiloxane membrane into a flowing liquid was investigated. The tubular configuration permits the exact determination of the convective diffusional contribution to membrane transport with models that account for fluid hydrodynamics. The observed transport behavior ranged from complete convective diffusion control for the hexyl ester to complete membrane control for the ethyl ester; the butyl ester exhibited a change in control with flow rate. The implications of convective diffusional considerations to intestinal absorption and dissolution studies are discussed.

4-Aminobenzoic Acid↗
PubMed1979

Metabolism and measurement of chloroprocaine, an ester-type local anesthetic.

Blood levels of intact chloroprocaine were determined using a GLC procedure capable of detecting as little as 10 ng of chloroprocaine/ml of blood. It was necessary to detective plasma cholinesterases in collected samples by adding echothiophate iodide to blood sampling tubes. An extraction procedure, followed by a TLC separation and spectrodensitometric assay, was developed for measurement of the metabolite 2-chloro-4-aminobenzoic acid in plasma and urine. With these procedures, data were obtained showing that chloroprocaine is hydrolyzed rapidly by plasma cholinesterases. No unchanged drug could be detected in any blood samples obtained from volunteers who received chloroprocaine by intravenous infusion or from obstetric patients who had epidural anesthesia during labor and delivery. Blood levels of 2-chloro-4-amino-benzoic acid rose promptly with the administration of chloroprocaine and declined rapidly after drug administration. Most of the metabolite was recovered in urine.

Anesthesia, Epidural↗
PubMed1981

Micellar solubilization of cetaben sodium in surfactant and lipid solutions.

Cetaben sodium solubilities were evaluated by micellar solubilization in various surfactants and lipid solvents. At pH 8, the relationship between cetaben sodium solubility and surfactant concentration delineated apparent saturable kinetics; at pH 4.9, the relationship between the two parameters was linear. In the presence of 0.5% sodium taurocholate and polysorbate 80, cetaben sodium solubility increased as the medium pH was increased; however, in the presence of 0.5% poloxamer 188, cetaben sodium solubility revealed a hyperbola when the pH was changed from 4.9 to 8.0. Cetaben sodium solubility was enhanced greatly by mixed physiological surfactants, full-strength caprylic-capric monodiglycerides or monodiglycerides, when compared to a single surfactant system. Cetaben sodium solubility is influenced by pH, surfactant type, surfactant concentration, lipid solvent type, and the simultaneous presence of surfactants or phospholipids.

4-Aminobenzoic Acid↗
PubMed1987

Effect of tablet solubility and hygroscopicity on disintegrant efficiency in direct compression tablets in terms of dissolution.

The effect of tablet composite solubility and hygroscopicity on the dissolution efficiency of three "super disintegrants", sodium starch glycolate, crospovidone, and croscarmellose sodium, was investigated. Lactose, dicalcium phosphate dihydrate, and sorbitol, alone or in combination, provided varying degrees of solubility and hygroscopicity to the direct compression tablet formulations. To monitor in vitro dissolution, 1% p-aminobenzoic acid was added to the formulation as a tracer. The results indicate that hygroscopic ingredients decrease the effectiveness of super disintegrants in promoting in vitro dissolution. The greater the overall hygroscopicity of the tablet formulation, the larger the decrease in the efficiency of the super disintegrant. Composite tablet solubility did not influence the effectiveness of the super disintegrants. Super disintegrants that complied with the same compendial specifications, but were manufactured by different companies, behaved similarly in promoting tablet dissolution.

Chemistry, Pharmaceutical↗
PubMed1991

Effect of formulation solubility and hygroscopicity on disintegrant efficiency in tablets prepared by wet granulation, in terms of dissolution.

The effect of tablet formulation solubility and hygroscopicity on the dissolution efficiency of three "super disintegrants" (sodium starch glycolate, crospovidone, and croscarmellose sodium) in tablets prepared by wet granulation was investigated. Lactose, calcium phosphate dibasic, sorbitol, and naproxen sodium, alone or in combination, provided varying degrees of solubility and hygroscopicity in the formulations. To monitor in vitro dissolution, 1% p-aminobenzoic acid was added to the formulation as a tracer. The results indicate that highly soluble and/or hygroscopic ingredients decrease the effectiveness of super disintegrants in promoting in vitro dissolution. The greater the overall hygroscopicity and solubility of the tablet formulation, the larger the decrease in the efficiency of the super disintegrant.

Calcium Phosphates↗
PubMed2006

Tissue distribution of N-acetyltransferase 1 and 2 catalyzing the N-acetylation of 4-aminobiphenyl and O-acetylation of N-hydroxy-4-aminobiphenyl in the congenic rapid and slow acetylator Syrian hamster.

N-acetyltransferase 1 (NAT1) and 2 (NAT2) enzymes catalyzing both deactivation (N-acetylation) and activation (O-acetylation) of arylamine carcinogens such as 4-aminobiphenyl (ABP) were investigated in a Syrian hamster model congenic at the NAT2 locus. NAT2 catalytic activities (measured with p-aminobenzoic acid) were significantly (P < 0.001) higher in rapid than slow acetylators in all tissues (except heart and prostate where activity was undetectable in slow acetylators). NAT1 catalytic activities (measured with sulfamethazine) were low but detectable in most tissues tested and did not differ significantly between rapid and slow acetylators. ABP N-acetyltransferase activity was detected in all tissues of rapid acetylators but was below the limit of detection in all tissues of slow acetylators except liver where it was about 15-fold lower than rapid acetylators. ABP N-acetyltransferase activities correlated with NAT2 activities (r2 = 0.871; P < 0.0001) but not with NAT1 activities (r2 = 0.132; P > 0.05). Levels of N-hydroxy-ABP O-acetyltransferase activities were significantly (P < 0.05) higher in rapid than slow acetylator cytosols for many but not all tissues. The N-hydroxy-ABP O-acetyltransferase activities correlated with ABP N-acetyltransferase activities (r2 = 0.695; P < 0.0001) and NAT2 activities (r2 = 0.521, P < 0.0001) but not with NAT1 activities (r2 = 0.115; P > 0.05). The results suggest widespread tissue distribution of both NAT1 and NAT2, which catalyzes both N- and O-acetylation. These conclusions are important for interpretation of molecular epidemiological investigations into the role of N-acetyltransferase polymorphisms in various diseases including cancer.

Acetylation↗
PubMed1993

Fluorometric determination of cyanate in plasma by conversion to 2,4(1H,3H)-quinazolinedione and separation by high-performance liquid chromatography.

A fluorometric high-performance liquid-chromatographic method is described for the determination of cyanate in human plasma. The method is based on the derivatization of cyanate with 2-aminobenzoic acid (anthranilic acid), leading to a stable cyclic fluorescent product, 2,4(1H,3H)-quinazolinedione. The fluorescent product was extracted with ethyl acetate, passed through a cation-exchange resin to eliminate the excess of derivatization reagent, and then concentrated on a Sep-Pak C-18 cartridge before reversed-phase chromatography and fluorometric detection. The precision of the method was satisfactory (coefficient of variation 2.3%) and the analytical recovery was quantitative (103%). Detection limit was found to be 8 nmol/liter from a 1-ml plasma sample. Cyanate in plasma was stable for 3 months when stored in liquid nitrogen. The mean and SD cyanate level in human plasma from 17 healthy nonsmoking subjects was 45 +/- 21 nmol/liter.

Adult↗
PubMed1994

Proteolyses of a fluorogenic insulin derivative and native insulin in reversed micelles monitored by fluorescence emission, reversed-phase high-performance liquid chromatography, and capillary zone electrophoresis.

The preparation and substrate properties of the fluorogenic insulin derivative N alpha A1-aminobenzoyl-N epilson B29-Tyr(NO2)- insulin are described. This semisynthetic protein intramolecularly quenched by long-range resonance energy transfer between the donor/acceptor pair 2-aminobenzoic acid and 3-nitrotyrosine was used to prove the activity of serine proteases toward substrates of high molecular weight after incorporation in reversed micelles. The proteases investigated, trypsin and alpha-chymotrypsin, were shown to be hydrolytically active in reversed micellar solvent systems stabilized by cetyltrimethylammonium bromide or sodium-1,2-bis(2-ethylhexylcarbonyl)-1- ethane sulfonate. Apart from fluorometric enzyme assays, methods for monitoring proteolyses in reversed micelles were elaborated using either reversed-phase high-performance liquid chromatography or capillary zone electrophoresis. Enzymatic digestions of native insulin by the specific protease trypsin and the less specific protease alpha-chymotrypsin were performed. In contrast to aqueous solution, high but still variable specificity of alpha-chymotrypsin which was dependent on the micellar environment was observed. The results promise further insight into the influence of interfacial environments on enzyme action and a novel approach to enzyme-mediated protein modifications by the use of microstructured solvent systems.

Chromatography, High Pressure Liquid↗
PubMed2001

Selective neurotensin-derived internally quenched fluorogenic substrates for neurolysin (EC 3.4.24.16): comparison with thimet oligopeptidase (EC 3.4.24.15) and neprilysin (EC 3.4.24.11).

Internally quenched fluorescent peptides derived from neurotensin (pELYENKPRRPYIL) sequence were synthesized and assayed as substrates for neurolysin (EC 3.4.24.16), thimet oligopeptidase (EC 3.4.24.15 or TOP), and neprilysin (EC 3.4.24.11 or NEP). Abz-LYENKPRRPYILQ-EDDnp (where EDDnp is N-(2,4-dinitrophenyl)ethylenediamine and Abz is ortho-aminobenzoic acid) was derived from neurotensin by the introduction of Q-EDDnp at the C-terminal end of peptide and by the substitution of the pyroglutamic (pE) residue at N-terminus for Abz and a series of shorter peptides was obtained by deletion of amino acids residues from C-terminal, N-terminal, or both sides. Neurolysin and TOP hydrolyzed the substrates at P--Y or Y--I or R--R bonds depending on the sequence and size of the peptides, while NEP cleaved P-Y or Y-I bonds according to its S'(1) specificity. One of these substrates, Abz-NKPRRPQ-EDDnp was a specific and sensitive substrate for neurolysin (k(cat) = 7.0 s(-1), K(m) = 1.19 microM and k(cat)/K(m) = 5882 mM(-1). s(-1)), while it was completely resistant to NEP and poorly hydrolyzed by TOP and also by prolyl oligopeptidase (EC 3.4.21.26). Neurolysin concentrations as low as 1 pM were detected using this substrate under our conditions and its analogue Abz-NKPRAPQ-EDDnp was hydrolyzed by neurolysin with k(cat) = 14.03 s(-1), K(m) = 0.82 microM, and k(cat)/K(m) = 17,110 mM(-1). s(-1), being the best substrate so far described for this peptidase.

Alanine↗
PubMed2001

Development of an internally quenched fluorescent substrate and a continuous fluorimetric assay for Streptococcus pneumoniae signal peptidase I.

Signal peptidase (SPase) I is responsible for the cleavage of signal peptides of many secreted proteins in bacteria and serves as a potential target for the development of novel antibacterial agents due to its unique physiological and biochemical properties. In this paper, we describe a novel fluorogenic substrate, KLTFGTVK(Abz)PVQAIAGY(NO2)EWL, in which 2-aminobenzoic acid (Abz) and 3-nitrotyrosine (Y(NO2)) were used as the fluorescent donor and acceptor, respectively. The substrate can be cleaved by both Streptococcus pneumoniae and Escherichia coli SPase I. Upon cleavage of the fluorogenic substrate by SPase I, the fluorescent intensity increases and can be monitored continuously by spectrofluorometer. Kinetic analysis with S. pneumoniae SPase I demonstrated that the K(m) value for the substrate is 118.1 microM, and the k(cat) value is 0.032 s(-1). Mass spectrometric analysis and peptide sequencing of the two cleaved products confirmed that the cleavage occurs specifically at the predicted site. More interestingly, the positively charged lysine in the N-terminus of the substrate was demonstrated to be important for effective cleavage. Phospholipids were found to stimulate the cleavage reaction. This stimulation by phospholipids is dependent upon the N-terminal charge of the substrate, indicating that the interaction of the positively charged substrate with anionic phospholipids is important for maintaining the substrate in certain conformation for cleavage. The substrate and assay described here can be readily automated and utilized for the identification of potential antibacterial agents.

Amino Acid Sequence↗
PubMed2001

Synthesis and hydrolysis by cysteine and serine proteases of short internally quenched fluorogenic peptides.

We developed sensitive substrates for cysteine proteases and specific substrates for serine proteases based on short internally quenched fluorescent peptides, Abz-F-R-X-EDDnp, where Abz (ortho-aminobenzoic acid) is the fluorescent donor, EDDnp [N-(ethylenediamine)-2,4-dinitrophenyl amide] is the fluorescent quencher, and X are natural amino acids. This series of peptides is compared to the commercially available Z-F-R-MCA, where Abz and X replace carbobenzoxy (Z) and methyl-7-aminocoumarin amide (MCA), respectively; and EDDnp can be considered a P(2)' residue. Whereas MCA is the fluorescent probe and cannot be modified, in the series Abz-F-R-X-EDDnp the amino acids X give the choice of matching the specificity of the S(1)' enzyme subsite, increasing the substrate specificity for a particular protease. All Abz-F-R-X-EDDnp synthesized peptides (for X = Phe, Leu, Ile, Ala, Pro, Gln, Ser, Lys, and Arg) were assayed with papain, human cathepsin L and B, trypsin, human plasma, and tissue kallikrein. Abz-F-R-L-EDDnp was the best substrate for papain and Abz-F-R-R-EDDnp or Abz-F-R-A-EDDnp was the more susceptible to cathepsin L. Abz-F-R-L-EDDnp was able to detect papain in the range of 1 to 15 pM. Human plasma kallikrein hydrolyzed Abz-F-R-R-EDDnp with significant efficiency (k(cat)/K(m) = 1833 mM(-1) s(-1)) and tissue kallikrein was very selective, hydrolyzing only the peptides Abz-F-R-A-EDDnp (k(cat)/K(m) = 2852 mM(-1) s(-1)) and Abz-F-R-S-EDDnp (k(cat)/K(m) = 4643 mM(-1) s(-1)). All Abz-F-R-X-EDDnp peptides were resistant to hydrolysis by thrombin and activated factor X.

Cathepsin B↗
PubMed2000

Crystal structure of Mycobacterium tuberculosis 7,8-dihydropteroate synthase in complex with pterin monophosphate: new insight into the enzymatic mechanism and sulfa-drug action.

The enzyme 7,8-dihydropteroate synthase (DHPS) catalyzes the condensation of para-aminobenzoic acid (pABA) with 6-hydroxymethyl-7, 8-dihydropterin-pyrophosphate to form 7,8-dihydropteroate and pyrophosphate. DHPS is essential for the de novo synthesis of folate in prokaryotes, lower eukaryotes, and in plants, but is absent in mammals. Inhibition of this enzyme's activity by sulfonamide and sulfone drugs depletes the folate pool, resulting in growth inhibition and cell death. Here, we report the 1.7 A resolution crystal structure of the binary complex of 6-hydroxymethylpterin monophosphate (PtP) with DHPS from Mycobacterium tuberculosis (Mtb), a pathogen responsible for the death of millions of human beings each year. Comparison to other DHPS structures reveals that the M. tuberculosis DHPS structure is in a unique conformation in which loop 1 closes over the active site. The Mtb DHPS structure hints at a mechanism in which both loops 1 and 2 play important roles in catalysis by shielding the active site from bulk solvent and allowing pyrophosphoryl transfer to occur. A binding mode for pABA, sulfonamides and sulfones is suggested based on: (i) the new conformation of the closed loop 1; (ii) the distribution of dapsone and sulfonamide resistance mutations; (iii) the observed direction of the bond between the 6-methyl carbon atom and the bridging oxygen atom to the alpha-phosphate group in the Mtb DHPS:PtP binary complex; and (iv) the conformation of loop 2 in the Escherichia coli DHPS structure. Finally, the Mtb DHPS structure reveals a highly conserved pterin binding pocket that may be exploited for the design of novel antimycobacterial agents.

Amino Acid Sequence↗
PubMed2000

Large-scale purification of myeloperoxidase from HL60 promyelocytic cells: characterization and comparison to human neutrophil myeloperoxidase.

A large-scale purification procedure was developed for the isolation of myeloperoxidase from HL60 promyelocytic cells in culture. Initial studies showed the bulk of peroxidase-positive myeloperoxidase activity to be located in the cetyltrimethylammonium bromide solubilized particulate fraction of cell homogenates. The myeloperoxidase was then chromatographically purified using concanavalin A followed by gel filtration. SDS-PAGE analysis of the final preparation showed the presence of only two proteins with molecular masses of approximately 55 and 15 kDa, corresponding to the large and small subunits of myeloperoxidase. These data, along with Reinheit Zahl (RZ) values (A(430)/A(280)) of greater than or equal to 0.72, indicate that the myeloperoxidase prepared by this method is apparently homogeneous. Preparations routinely yielded 12-20 mg of pure myeloperoxidase per 10 ml of cell pellet. The HL60 myeloperoxidase was shown to be indistinguishable from purified human neutrophil myeloperoxidase by size exclusion chromatography, analytical ultracentrifugation, SDS-PAGE, Western blot, and NH(2)-terminal sequence analysis. The activities of the two myeloperoxidase samples, as measured using either the tetramethylbenzidine or the taurine chloramine assay, were indistinguishable. Finally, both enzymes responded identically to dapsone and aminobenzoic acid hydrazide, known inhibitors of myeloperoxidase. A protocol is presented here for the rapid, large-scale purification of myeloperoxidase from cultured HL60 cells, as well as evidence for the interchangeability of this myeloperoxidase and that purified from human neutrophils.

Benzidines↗
PubMed1994

Construction of Syrian hamster lines congenic at the polymorphic acetyltransferase locus (NAT2): acetylator genotype-dependent N- and O-acetylation of arylamine carcinogens.

Congenic Bio. 1.5/H-NAT2 Syrian hamster lines were constructed by introducing the NAT2r gene from MHA/SsLak inbred hamsters into a background BIO 1.5 Syrian inbred hamster line. Genetic identity of the Bio. 1.5/H-NAT2 congenic lines and nonidentity with the previously constructed Bio. 82.73/H-Pat congenic lines were determined by "DNA fingerprints" of genomic DNA derived from the different hamster lines. The N-acetylation capacity of the Bio. 1.5/H-NAT2 congenic hamster lines was clearly NAT2-dependent both in vivo and in vitro, with highest levels expressed in Bio. 1.5/H-NAT2r homozygous rapid acetylators, intermediate levels in Bio. 1.5/H-NAT2r/NAT2s heterozygous acetylators, and lowest levels in Bio. 1.5/H-NAT2s homozygous slow acetylators. The NAT2-dependent expression of N-acetyltransferase activity was evident toward p-aminobenzoic acid, 4-aminophenol, 2-aminofluorene, 4-aminobiphenyl, beta-naphthylamine, and 3,2'-dimethyl-4-amino-biphenyl in liver, kidney, colon, lung, and urinary bladder cytosols. The polymorphic acetyltransferase (NAT2) and the monomorphic acetyltransferase (NAT1) were isolated from hepatic cytosols and tested separately for their ability to catalyze arylamine N-acetyltransferase and N-hydroxyarylamine O-acetyltransferase activities. Both arylamine N-acetylation and N-hydroxyarylamine O-acetylation were clearly acetylator genotype-dependent when catalyzed by NAT2, and both were clearly acetylator genotype-independent when catalyzed by NAT1. NAT2/NAT1 activity ratios varied with the particular arylamine substrate acetylated. These studies show an important role for NAT2 acetylator genotype in Syrian hamster carcinogenic arylamine metabolism and confirm its role in the metabolic activation of N-hydroxyarylamines. The Bio. 1.5/H-NAT2 congenic lines provide a new model for investigating the precise role of the NAT2 gene locus in arylamine metabolism and toxicity.

Acetylation↗