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PubMed1987

Structure of the oligosaccharide portion of human hepatitis B surface antigen.

The hepatitis B surface antigen, which constitutes the currently available vaccine, is the empty envelope of the hepatitis B virus. We investigated the carbohydrate structures of the envelope glycoproteins. The intact oligosaccharides were enzymatically released from the coat glycoproteins using peptide-N4-(N-acetyl-beta-glucosaminyl) asparagine amidase F and isolated by gel permeation chromatography. Cesium ion liquid secondary ion mass spectra of the intact, underivatized oligosaccharides showed molecular weights of 1932, 2078, and 2223. The mixture included partially and totally sialylated structures, a fraction (approximately 8%) of which were substituted with a single terminal fucose residue; no desialylated oligosaccharides were detected. The reducing termini of the oligomers were derivatized by reduction of the Schiff base formed using p-aminobenzoic acid ethyl ester, and fragmentation patterns identical to those produced from standard biantennary complex oligosaccharides were obtained. Methylation linkage analysis of the oligosaccharides showed that the carbohydrate composition and the mannose branching patterns also resembled those of a biantennary oligosaccharide. The results of this study indicate that glycosylation of the hepatitis B surface antigen, which takes place in the liver, is typical of other serum glycoproteins made in the liver; and this analytical strategy, including cesium ion liquid secondary ion mass spectrometry, is an effective approach for the structural analysis of complex carbohydrates available in only the 1-10 micrograms sample size range.

Chromatography, High Pressure Liquid↗
PubMed1988

3-Aminobenzamide inhibits poly(ADP ribose) synthetase activity and induces phosphoenolpyruvate carboxykinase (GTP) in H4IIE hepatoma cells.

The purpose of this study was to determine whether changes in ADP-ribosylation affect expression of the gene encoding the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) in H4IIE hepatoma cells. Treatment with 3-aminobenzamide, a specific inhibitor of poly(ADP ribose) synthetase, caused an 89% decrease of ADP-ribosylation in isolated nuclei, and resulted in a two- to threefold induction of immunoassayable PEPCK in cultured cells. In contrast, the structurally related compound p-aminobenzoic acid had no significant effect on either process. In vivo labeling of proteins with [35S]methionine, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography, showed that the induction of immunoreactive PEPCK by 3-aminobenzamide was due to a selective increase in the synthesis of the protein. The specific induction of PEPCK synthesis by 3-aminobenzamide was accounted for by a twofold increase of mRNAPEPCK which reached its maximal value 4 h after the addition of 3-aminobenzamide and returned to the basal level by 10 h. A possible role of ADP-ribosylation in cAMP or glucocorticoid induction of PEPCK was investigated in experiments in which H4IIE cells were treated with combinations of 3-aminobenzamide and either dexamethasone or a cAMP analog. In each case the effects on PEPCK induction were additive, indicating that glucocorticoids and cAMP induce PEPCK by pathways different from that used by 3-aminobenzamide.

Adenosine Diphosphate Ribose↗
PubMed1991

Further characterization of allergenically active oligosaccharitols isolated from a sea squirt H-antigen.

Complete primary structures of five allergenically active oligosaccharitols (HPG-beta 2-N5a, -N6, -N7a, -N7b, and -N9) derived from a sea squirt H-antigen were studied. Structural characterization was carried out by a new method in which products of limited periodate oxidation, followed by derivatization with p-aminobenzoic acid ethyl ester, were analyzed by a combination of HPLC, fast atom-bombardment mass spectrometry, sequential glycosidase digestion, methylation analysis, and 500-MHz 1H NMR. Established structures of GalNAc beta 1-4 (GalNAc alpha 1-2Fuc alpha 1-3) GlcNAc beta 1-3GalNAc-ol, GalNAc beta 1-4GlcNAc beta 1-3 (GalNAc beta 1-4GlcNAc beta 1-6) GalNAc-ol, GalNAc beta 1-4GlcNAc beta 1-3[GalNAc beta 1-4 (Fuc alpha 1-3) GlcNAc beta 1-6] GalNAc-ol, GalNAc beta 1-4 (Fuc alpha 1-3) GlcNAc beta 1-3[GalNAc beta 1-4 (Fuc alpha 1-3) GlcNAc beta 1-6] GalNAc-ol, and GalNAc beta 1-4 (GalNAc alpha 1-2Fuc alpha 1-3)GlcNAc beta 1-3 [GalNAc beta 1-4 (GalNAc alpha 1-2Fuc alpha 1-3)GlcNAc beta 1-6]GalNAc-ol are represented by HPG-beta 2-N5a, -N6, -N7a, -N7b, and -N9, respectively. These structures have not been encountered previously. Oligosaccharide units GalNAc alpha 1-2Fuc alpha 1-, GalNAc beta 1-4GlcNAc beta 1-, and Fuc alpha 1-3GlcNAc beta 1- are considered to be the allergenically specific epitopes. Partial assignments of 500-MHz 1H NMR spectra of these novel O-linked oligosaccharitols were attempted.

Allergens↗
PubMed1980

Mechanisms for the production of DNA damage in cultured human and hamster cells irradiated with light from fluorescent lamps, sunlamps, and the sun.

Light from fluorescent lamps has recently been shown to be toxic and mutagenic to V-79 hamster cells. In this report it is shown that visible light (> 295 nm) from fluorescent lamps, sunlamps and the sun produces DNA single-strand breaks in hamster or human cells irradiated with these sources. Some of the DNA breaks and the mutagenic action of the light can be averted by filtering the light through para-aminobenzoic acid, which filters out wavelengths below 345 nm. The radical scavengers dimethyl sulfoxide, glycerol, and potassium iodide can also protect the cells from some of the DNA breaks, but the scavengers do not protect V-79 cells from the mutagenic action of the light sources. Hydrogen peroxide and riboflavin and tryptophan photoproducts also are shown to produce DNA breaks in V-79 cells; however, these treatments are not mutagenic to V-79 cells. These data suggest that several types of lesions may be produced in the DNA of irradiated cells by several different mechanisms, and that some of the lesions may be related to toxicity and mutagenicity of the light sources, and others may not.

Animals↗
PubMed1988

Properties of cutaneous acetyltransferase catalyzing N- and O-acetylation of carcinogenic arylamines and N-hydroxyarylamine.

The role of skin for N- and O-acetylations of carcinogenic arylamine and N-hydroxyarylamine was studied in vitro. Unexpectedly high activities were observed in acetyl CoA-dependent N-acetylations of 2-aminofluorene (2-AF) and p-aminobenzoic acid (PABA) in skin cytosols of hamsters. The specific activity for 2-AF (4.52 nmoles/mg protein per min) was largely the same as that of rat liver cytosols. The cutaneous cytosols also catalyzed N,N-acetyltransfer reaction from N-hydroxy-4-acetylamino-biphenyl (N-OH-AABP) to 2-AF and acetyl CoA-dependent O-acetylation of 2-hydroxyamino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (N-OH-Glu-P-1), suggesting that hamster skin cytosol has enzymes similar to hepatic acetyltransferases. In addition, remarkably high correlations were observed between the skin and liver in the activities for N-acetylations of PABA and 2-AF. In a colony of Syrian golden hamsters a clear polymorphism was detected in the cutaneous N-acetylations of PABA and 2-AF. These animals were divided into three groups according to their activities: rapid, intermediate and slow acetylators. On the other hand, the acetylating activities in the skin and liver of these three groups showed monomorphic distribution with N-OH-AABP-dependent N,N-acetyltransfer of 2-AF and acetyl CoA-dependent O-acetylation of N-OH-Glu-P-1. These results, together with the detection of N-acetylating activity in the skin of other experimental animals and humans, suggest that skin may play an important role in the metabolism of aromatic amines and that the cutaneous acetylation in hamsters may be under the common genetic control which regulates the individual difference in the hepatic activities.

Acetylation↗
PubMed1990

An isozyme-selective affinity label for rat hepatic acetyltransferases.

Affinity chromatography of an ammonium sulfate precipitate obtained from rat hepatic cytosol resulted in the separation of two fractions of N-acetyltransferase (NAT) activity. NATI catalyzed the S-acetylcoenzyme A (AcCoA)-dependent acetylation of p-aminobenzoic acid (PABA); NAT II catalyzed the N-hydroxy-2-acetylaminofluorene (N-OH-AAF)-dependent acetylation of 4-amino-azobenzene (AAB) (N,N-acetyltransferase), the AcCoA-dependent acetylation of procainamide (PA), and the N-arylhydroxamic acid N,O-acyltransferase (AHAT) activity that results in the conversion of N-OH-AAF and related hydroxamic acids to electrophilic reactants. 1-(Fluoren-2-yl)-2-propen-1-one (vinyl fluorenyl ketone, VFK) was shown to be a potent and irreversible inactivator of NAT II activities. A 200-fold higher concentration of VFK was required to inactivate NAT I activity than was required for inactivation of NAT II activities. Similar selectivity in the inactivation of the isozymes was observed when experiments were conducted with enzyme preparations that contained both NAT I and NAT II activities. The presence of substrates and products of the NAT II-catalyzed reactions such as AcCoA, 2-acetylaminofluorene (2-AAF), and N-acetyl-4-aminoazobenzene (N-Ac-AAB) protected NAT II from the inactivating effects of VFK, providing evidence that VFK is an active site directed inhibitor (affinity label) of NAT II. Studies with 1-(fluoren-2-yl)-2-propan-1-one (EFK), an analogue of VFK in which the alpha, beta-unsaturated vinyl ketone group of VFK has been replaced with an ethyl ketone group, demonstrated that the conjugated ketone of VFK is required for inactivation of enzyme activity. The results of these studies suggest that agents such as VFK should have utility as probes of acetyltransferase multiplicity and in the investigation of the active site topography of the enzymes.

Acetylation↗
PubMed1979

A sensitive fluorescent assay for N-acetyltransferase activity in human lymphocytes from newborns and adults.

We have developed a simplified assay for the enzyme N-acetyltransferase, based upon the loss of fluorescence after acetylation of the substrate p-aminobenzoic acid. This method is sufficiently sensitive to permit the quantitation of N-acetyltransferase activity in 10(5) human lymphocytes. Using this method, we have compared the level of N-acetyltransferase activity in lymphocytes from adult peripheral blood and from cord blood samples.

Acetyltransferases↗
PubMed1983

Relationship between PABA and Lundh tests: lack of influence of duodenal pH in vivo.

Twenty-five patients with chronic pancreatitis and 25 patients with non-pancreatic abdominal disorders were investigated by Lundh and BT PABA/14C-PABA tests of pancreatic function. The following results emerged: (1) There was a strong positive linear relationship between mean trypsin activity (MTA) and mean chymotrypsin activity (MCA) in duodenal aspirates after a Lundh test meal. (2) There was a strong positive linear relationship between chymotrypsin activity measured with BTEE, or BT PABA as substrate. (3) There was a strong positive correlation between MTA, or MCA, in duodenal juice after a Lundh meal and urinary PABA recovery, or the PABA/14C excretion index (PEI) in patients with chronic pancreatitis, but not in controls. (4) There was no correlation between the pH of duodenal juice in Lundh tests and PABA recovery, or PEI, in patients with or without pancreatic disease. We conclude that the Lundh and BT PABA/14C-PABA tests are equally discriminatory methods of assessing pancreatic exocrine function. The rate limiting effect of pH on BT PABA hydrolysis reported in in-vitro studies does not affect the practical clinical value of the BT PABA/14C-PABA test.

4-Aminobenzoic Acid↗
PubMed1983

Observations on the BT PABA/14C-PABA tubeless test of pancreatic function.

The diagnostic accuracy of the BT PABA/14C-PABA tubeless test of pancreatic function was assessed in a prospective study of 140 patients. Drug or isotopic interference invalidated 16 tests (11.4%). The sensitivity of the PABA/14C excretion index was 76.7% and the specificity 85.7% using the mean -2 SD value of 0.82 as the cut-off point; 74.4% sensitivity and 95.7% specificity using the mean -3 SD value of 0.76. The potential usefulness and limitations of this modern version of the PABA test are discussed.

4-Aminobenzoic Acid↗
PubMed1988

Colorimetric method for assay of serum gamma-glutamyltransferase activity with some L-gamma-glutamyl-carboxyanilides.

A simple method for the assay of serum gamma-glutamyltransferase activity with soluble L-gamma-glutamyl-carboxyanilides is presented. It is based on transformation of aminobenzoic acid liberated by the enzyme into colour complex with 4-dimethyl-aminobenzaldehyde or with 4-dimethylaminocinnamaldehyde in acid medium. Among three carboxyanilides studied the highest enzyme activity was noted with L-gamma-glutamyl-3-carboxyanilide and no activity with L-gamma-glutamyl-2-carboxyanilide. A good correlation was demonstrated for serum gamma-glutamyltransferase activity determined by the new colorimetric method and by the standard one with L-gamma-glutamyl-3-carboxy-4-nitroanilide.

Anilides↗
PubMed1984

Inhibitors of an enkephalin degrading membrane-bound metalloendopeptidase: analgesic properties and effects on striatal enkephalin levels.

Intraperitoneal administration of N-[1-(R,S)-carboxy-2-phenylethyl-Phe-p-aminobenzoate, synthesized in this laboratory as a potent inhibitor of membrane-bound metalloendopeptidase (EC 3.4.24.11) caused a prolonged but weak analgesic effect on rats as measured by the tail flick test. It also caused a transitory but significant increase in striatal [Leu5]- and [Met5]enkephalin levels 3 h, after administration. Analogs of the inhibitor in which the phenylalanyl residue was replaced by an alanyl or glycyl residue also elicited prolonged analgesic responses although their inhibitory potencies were 75 and more than 1500 times lower respectively. The glycine containing derivative did not alter striatal enkephalin levels 3 h, after administration. The data suggest that inhibition of the metalloendopeptidase decreases the rate of degradation of endogenous enkephalins, however the analgesic properties of the inhibitors do not seem to be related to their inhibitory potencies. Factors other than changes in striatal enkephalin levels may contribute to the analgesic effect of the three N-carboxyphenylethyl derivatives.

4-Aminobenzoic Acid↗
PubMed1990

A distinct thimet peptidase from rat liver mitochondria.

Thimet peptidase has been purified from rat liver mitochondria and found to share the characteristics of a thiol-dependent metallo-endopeptidase previously described for an enzyme in the cytosolic fraction from rat testis: inhibition by EDTA, reactivation by Zn2+, requirement of dithiothreitol for maximal and stable activity, and inhibition by N-ethylmaleimide. The Ki for inhibition by N-[1-(RS)-carboxy-3-phenylpropyl]-Ala-Ala-Phe-p-aminobenzoic acid is 2.6 microM, 100-fold higher than the value for the cytosolic form. The mitochondrial form is not inhibited by antisera against the cytosolic form, and the two forms of the enzyme show quantitative differences in substrate specificity. The name thimet peptidase II is suggested for the enzyme from rat mitochondria.

Amino Acid Sequence↗
PubMed1987

Determination of reducing and non-reducing carbohydrates in food products by liquid chromatography with post-column catalytic hydrolysis and derivatization. Comparison with refractive index detection.

Post-column catalytic hydrolysis combined with 4-aminobenzoic acid hydrazide derivatization is employed for the determination of both reducing and non-reducing carbohydrates in a variety of complex sample matrices such as dairy products, processed foods and tobaccos. Comparison with refractive index detection shows the post-column method to be superior from the standpoint of selectivity, sensitivity and simplicity of sample preparation. Limits of detection are in the low-nanogram range. Quantitative results are presented for the determination of sugars in potato extracts. The method is also applicable for the separation and detection of carbohydrate oligomers.

Beverages↗
PubMed1986

Analysis of resistance to pyrimethamine/sulphadoxine of isolates of Plasmodium falciparum from Eastern Thailand.

The in vitro susceptibility of five field isolates of Plasmodium falciparum from the region of the Thai-Kampuchean border to pyrimethamine, sulphadoxine, and their combination, was determined using a microtitre test system and media deficient in p-aminobenzoic acid and folic acid. Two-fold serial dilutions of pyrimethamine ranging from concentrations of 8.0 to 0.125 microM and sulphadoxine ranging from 800 to 50 microM were evaluated for antimalarial activity. Viability was based on the maturation of the ring stages to normally-appearing schizonts. Tested singly the parasites had an average ID90 of 3.82 microM for pyrimethamine and greater than 800 microM for sulphadoxine. Analysis of the drugs interaction showed maximum potentiation at approximately 0.8 microM of pyrimethamine and 80 microM of sulphadoxine. These results suggest that resistance to Fansidar is due to the resistance to both components. Although there was a potentiating effect it was probably not sufficient enough for the drugs to be effective in vivo. This may, in part, explain the reduction in clinical cures with the sulphadoxine-pyrimethamine combination in eastern Thailand.

Drug Resistance, Microbial↗
PubMed1987

Synergistic antimalarial activity of dapsone/dihydrofolate reductase inhibitors and the interaction of antifol, antipyrimidine and antipurine combinations against Plasmodium falciparum in vitro.

Using low folate, low p-aminobenzoic acid medium, 2 isolates of Plasmodium falciparum were tested in vitro against a wide range of antimetabolite compounds with known or potential antimalarial activity. ID50 values (the concentration of compound causing 50% inhibition of [3H]hypoxanthine incorporation) were determined for each compound against both isolates. The compounds tested may affect folate, pyrimidine or purine metabolism in malaria parasites and various combinations of compounds were examined for further synergistic antimalarial effects. The combination of any of the dihydrofolate reductase inhibitors cycloguanil, pyrimethamine or WR 99210 with the sulphone drug dapsone demonstrated strongly synergistic antimalarial activity. Combinations of dihydrofolate reductase inhibitors with the antipyrimidine compounds pyrazofurin or menoctone, or with the antipurine compounds tubercidin, bredinin or hadacidin, or with primaquine, failed to demonstrate synergistic activity. Most combinations of an antipurine with an antipyrimidine compound also failed to show any synergistic effect. However, weak synergism was consistently seen in the tubercidin/pyrazofurin and tubercidin/menoctone combinations. Over the 48 h intraerythrocytic cycle using tightly synchronized parasites, tubercidin demonstrated both a cytotoxic and a cytostatic effect.

Animals↗
PubMed1991

The role of N-hydroxyphenetidine in phenacetin-induced hemolytic anemia.

Phenacetin is well known to cause hemolytic anemia and methemoglobinemia in humans. Early mechanistic studies clearly established a causal role for active/reactive drug metabolites in the process but did not unequivocally identify these metabolite(s) or resolve the question of whether these two hemotoxicities are mechanistically linked. As part of ongoing studies on the mechanism underlying arylamine-induced hemotoxicities, we have recently shown that the arylhydroxylamine metabolites of aniline and dapsone mediate the hemolytic activity of aniline and dapsone, respectively. The present study was undertaken to determine if N-hydroxyphenetidine (PNOH), the known arylhydroxylamine metabolite of phenacetin, is responsible for phenacetin-induced hemolytic anemia. As measured by decreased survival of 51Cr-labeled erythrocytes in rats, phenacetin, p-phenetidine, and PNOH were all hemolytic in vivo, with PNOH being significantly the most potent of the three. In vitro exposure of 51Cr-tagged erythrocytes to PNOH, followed by transfusion into isologous rats, resulted in a concentration-dependent reduction in erythrocyte survival, indicating that PNOH is a direct-acting hemolytic agent. Phenacetin and p-phenetidine were inactive. Phenacetin, p-phenetidine, and PNOH all produced dose-dependent methemoglobinemia in rats. In parallel in vitro studies, PNOH elevated methemoglobin levels, p-phenetidine and phenacetin did not. However, attempts to identify PNOH in the blood of phenacetin- and p-phenetidine-treated rats were unsuccessful, despite the use of a highly sensitive analytical method. Hemotoxic concentrations of PNOH were found to be highly unstable in the presence of red cells, though relatively stable in the buffer vehicle alone. Inhibitors of acetylation (p-aminobenzoic acid [PABA]) and deacetylation (bis-[p-nitrophenyl]phosphate [BNPP]), used to alter the cyclic interconversion of phenacetin and p-phenetidine, caused changes in phenacetin hemotoxicity that indicated the hemotoxin was a deacetylated metabolite distal to p-phenetidine. These data are consistent with the hypothesis that PNOH, formed during the metabolic clearance of phenacetin, mediates phenacetin-induced hemolytic anemia and methemoglobinemia through direct toxic actions in the erythrocyte.

Anemia, Hemolytic↗