| 1926162 |
Uptake and subcellular localization of tritiated dihydro-microcystin-LR in rat liver |
10.1016/0041-0101(91)90053-t. |
Toxicon |
Uptake and subcellular localization of tritiated dihydro-microcystin-LR in rat liver
Abstract
- Microcystin-LR (MC-LR), a cyclic heptapeptide hepatotoxin (mol. wt = 994) produced by the blue-green alga (cyanobacterium), Microcystis aeruginosa, was reduced with tritium labeled sodium borohydride, converted to 3H-dihydro-microcystin-LR ( 3H-2HMC-LR), and purified to greater than 99% purity by C-18 reverse-phase high-performance liquid chromatography. The uptake and subcellular distribution of 3H-2HMC-LR were determined in suspensions of hepatocytes at 0 degrees C and 37 degrees C, or following rifampicin pretreatment, and in perfused rat liver. The remaining cells were homogenized and subfractionated using sucrose gradient centrifugation. Suspensions of 7.5 x 10(6) hepatocytes also were incubated with 10 micrograms/ml of toxin, solubilized in Triton X-100, and ultracentrifuged to pellet the detergent insoluble fraction (containing actin). Isolated rat livers were perfused with media containing 3H-2HMC-LR and the uptake of radiolabel was determined. Sequential biopsy samples were collected for histologic examination. The remaining liver was homogenized and subcellular fractions prepared. Uptake of radiolabel was rapid in both cell suspension at 37 degrees C and perfused liver; however, uptake in cell suspensions was reduced by about 50% at 0 degrees C and by rifampicin (50 micrograms/ml) pretreatment. Hepatocyte necrosis was observed in isolated perfused livers 45 min after initiation of perfusion with 3H-2HMC-LR. In both hepatocyte suspensions and perfused livers 65 to 77% of the radiolabel was in the cytosolic fraction. In the hepatocyte suspensions, 13 to 18% of the radiolabel was present in the plasma membrane/nuclear fraction with lesser amounts in the other fractions. Trichloroacetic acid treatment of cytosolic fractions indicated that in hepatocyte suspensions, 50-60% of the radiolabel was bound to cytosolic protein. Studies using the perfused liver confirmed that the majority of the radiolabeled MCLR (78-88%) was bound to cytosolic protein. These data suggest that the uptake of 3H-2HMC-LR occurs primarily by an energy-dependent transport process involving the rifampicin-sensitive hepatic bile acid carrier and that once inside the hepatocyte, the toxin binds to a cytosolic protein(s).
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| 1930286 |
DNA base damage by beta-lactam, tetracycline, bacitracin and rifamycin antibacterial antibiotics |
10.1016/0006-2952(91)90429-9. |
Biochem Pharmacol |
DNA base damage by beta-lactam, tetracycline, bacitracin and rifamycin antibacterial antibiotics
Abstract
- Several antibacterial antibiotics have been shown to participate with transition metal ions in chemical reactions leading to the formation of reactive oxygen species. An important host defence mechanism for dealing with invading bacteria involves the production of reactive oxygen species, such as superoxide, hydrogen peroxide and hypochlorous acid, by phagocytic cells. The production of reactive oxygens by redox cycling antibacterial antibiotics has led us to suggest that a 'phagomimetic' contribution may also be made in vivo. Here we show that four structurally different antibacterial antibiotics, in the presence of added copper salt, bring about oxidative modification to bases in DNA detected using gas chromatography-mass spectrometry. The drug most damaging to DNA was rifamycin SV which was more active than a reference mixture of hydrogen peroxide and ascorbic acid."
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| 1930826 |
Structure of a new cyclotetrapeptide trapoxin A |
10.1107/s0108270190012987. |
Acta Crystallogr C |
Structure of a new cyclotetrapeptide trapoxin A
Abstract
- C34H42N4O6, Mr = 602.73, triclinic, P1, a = 14.707 (2), b = 15.559 (2), c = 13.026 (1) A, alpha = 112.23 (1), beta = 97.25 (1), gamma = 60.67 (1) degree, V = 2399.1 (6) A3, Z = 3, Dx = 1.251 Mg m-3, lambda(Cu K alpha) = 1.54178 A, mu = 0.71 mm-1, F(000) = 966, T = 295 K, R = 0.042 for 7802 observed reflections Fo greater than 3 sigma (Fo). The structure of trapoxin A was determined as cyclo-(S)-phenylalanyl-(S)-phenylalanyl-(R)-pipecolinyl- (2S,9S)-2-amino-8-oxo-9,10-epoxydecanoyl-. There are three crystallographically independent molecules in the cell. These molecules are linked to each other by NH...O hydrogen bonds to form an infinite chain extending along the a axis.
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| 1932561 |
Conformational analysis of bacitracin A, a naturally occurring lariat |
10.1002/bip.360310604. |
Biopolymers |
Conformational analysis of bacitracin A, a naturally occurring lariat
Abstract
- The proton nmr spectra of bacitracin A in H2O and DMSO-d6 have been assigned and the conformational behavior of the peptide in the two solvents has been compared. Although bacitracin A shows a conformational equilibrium between at least two conformations differing in the relative position of the cyclic and linear domains of the molecule, the spectra in water can be interpreted in terms of a preferred conformation in which the linear part is folded over the cyclic moiety and a turn is present around Ile(8)-DPhe(9).
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| 1934186 |
Conformational studies of cyclo(L-Phe-L-Pro-Gly-L-Pro)2 by 13C nuclear magnetic resonance |
10.1248/cpb.39.1617. |
Chem Pharm Bull (Tokyo) |
Conformational studies of cyclo(L-Phe-L-Pro-Gly-L-Pro)2 by 13C nuclear magnetic resonance
Abstract
- The 13C-NMR spectrum (Fig. 2,1) of cyclooctapeptide cyclo(L-phe-L-Pro-Gly-L-Pro)2 (A) in CDC13 suggested that its conformation involved the coexistence of two kinds of C2-symmetric conformation with trans-trans-trans-trans and cis-trans-trans-trans forms. Adding 0.5 equivalent of CsSCN or one equivalent of DL-Phe-OMe.HCl to the solution of cyclopeptide (A) in CDC13 yielded 13C-NMR spectra (Fig. 2,2 and Table I) which suggested a single C2-symmetric conformation with trans-trans-trans-trans form, resulting from the formation of complexes with CsSCN or DL-Phe-OMe.HCl. The 13C-NMR spectrum of complexes of A with DL-Phe-OMe.HCl displayed separate resonances for C(gamma), C(o), C(m), C(alpha), and C(beta) of D-Phe-OMe.HCl and L-Phe-OMe.HCl (Table I).
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| 1935953 |
Identification and characterization of the lantibiotic nisin Z, a natural nisin variant |
10.1111/j.1432-1033.1991.tb16317.x. |
Eur J Biochem |
Identification and characterization of the lantibiotic nisin Z, a natural nisin variant
Abstract
- Lactococcus lactis strain NIZO 22186 produces an extracellular, lanthionine-containing 3.5-kDa polypeptide with antimicrobial activity. Its retention time on reversed-phase (RP) HPLC and its amino acid composition showed high similarities but no complete identity to nisin. The gene for this lantibiotic, designated nisZ, has been cloned and its nucleotide sequence was found to be identical to that of the precursor nisin gene apart from a single mutation resulting in the substitution His27Asn in the mature polypeptide. NMR studies of the natural nisin variant, which has been designated nisin Z, confirmed the His27Asn substitution and indicated that it has a similar structure to nisin.
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| 1935967 |
Isolation and characterization of a new variant of surfactin, the Val7surfactin |
10.1111/j.1432-1033.1991.tb16349.x. |
Eur J Biochem |
Isolation and characterization of a new variant of surfactin, the Val7surfactin
Abstract
- Reinvestigation of surfactin, a previously studied peptidolipid surfactant from Bacillus subtilis, by fast-atom-bombardment mass spectrometry and 1H-NMR spectroscopy, as well as by chemical methods, revealed the presence of a closely related second constituent. This new compound, Val7surfactin, differs from the known surfactin by the C-terminal amino acid residue which is valine instead of leucine.
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| 1938108 |
NMR studies on the conformation of cyclodipeptides with two identical L-aromatic amino acid residues in solutions--cycloL-5(OH)Trp-L-5(OH)Trp and cyclo-L-Phe-L-Phe |
10.1111/j.1399-3011.1991.tb01402.x. |
Int J Pept Protein Res |
NMR studies on the conformation of cyclodipeptides with two identical L-aromatic amino acid residues in solutions--cycloL-5(OH)Trp-L-5(OH)Trp and cyclo-L-Phe-L-Phe
Abstract
- NMR studies on the conformations of cyclodipeptides containing two identical L-aromatic amino acid residues cyclo-L-5(OH)Trp-L-5(OH)Trp8 and cyclo-L-Phe-L-Phe9 in DMSO solutions are reported here. The 1H chemical shifts, the spin-spin coupling constants, and the NOE results show that in these two cyclodipeptides one residue occupies the folded antiperpendicular and the second the extended to nitrogen perpendicular conformers respectively. The results indicate that each of the identical residues is in a fast conformational equilibrium between the above two conformers so that one set of 1H and 13C resonances is observed for the two identical residues in the above two cyclodipeptides.
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| 1938614 |
Structure of aureobasidin A |
10.7164/antibiotics.44.925. |
J Antibiot (Tokyo) |
Structure of aureobasidin A
Abstract
- Aureobasidin A, a new antifungal antibiotic, was isolated from the culture medium of Aureobasidium pullulans R106. Aureobasidin A was a cyclic depsipeptide consisting of eight alpha-amino acid units and one hydroxy acid unit. The structures of the units were found by acid hydrolysis of the antibiotic to be 2(R)-hydroxy-3(R)-methylpentanoic acid, beta-hydroxy-N-methyl-L-valine, N-methyl-L-valine, L-proline, allo-L-isoleucine, N-methyl-L-phenylalanine, L-leucine, and L-phenyl-alanine. The sequence of the units was identified by NMR and FAB-MS of the products from the alkaline hydrolysis of aureobasidin A.
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| 1939462 |
Direct in vitro and in vivo monitoring of destruxins metabolism in insects using internal surface reversed-phase high-performance liquid chromatography. I. Behaviour of E destruxin in locusts |
10.1016/0378-4347(91)80268-h. |
J Chromatogr |
Direct in vitro and in vivo monitoring of destruxins metabolism in insects using internal surface reversed-phase high-performance liquid chromatography. I. Behaviour of E destruxin in locusts
Abstract
- High-performance liquid chromatography with internal surface reversed-phase packing provides an analytical tool for studying the in vitro and in vivo metabolism of A and E destruxins in the haemolymph and various organs of male adults of Locusta migratoria. A slight amount of injected E destruxin is shown to be hydrated into E-diol destruxin in the haemolymph. The rest of the toxin is recovered unchanged in the fat-body, pericardial tissues and Malpighian tubules, and some further E-diol destruxin formation occurs in these organs. Because E-diol destruxin is only weakly toxic, this appears to be a detoxication process.
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| 1953640 |
Separation of important new platelet glycoproteins (GPIa, GPIc, GPIc*, GPIIa and GMP-140) by F.P.L.C. Characterization by monoclonal antibodies and gas-phase sequencing. |
10.1042/bj2790419 |
Biochem. J. |
Separation of important new platelet glycoproteins (GPIa, GPIc, GPIc*, GPIIa and GMP-140) by F.P.L.C. Characterization by monoclonal antibodies and gas-phase sequencing.
Abstract
- A large number of membrane glycoproteins (around 40) are present on the surface of human blood platelets. Some of these glycoproteins are expressed in relatively small amounts, and their functions, as well as their structure, remain to be elucidated. The aim of the present study was to separate rapidly, under non-denaturing conditions, and characterize minor glycoproteins such as Very Late Antigens (VLA) (GPIa, GPIc, GPIc* and GPIIa) and GMP-140 (also known as PADGEM). VLAs and GMP-140 are respectively members of the integrin and selectin families. Platelet membrane glycoproteins were separated by wheat-germ agglutinin lectin affinity and Mono Q anion-exchange f.p.l.c. Peaks bearing isolated glycoproteins were electrophoresed on one- or two-dimensional SDS/polyacrylamide gels, Western blotted on to Immobilon poly(vinylidene difluoride) membranes and gas-phase-sequenced. The identity of isolated glycoproteins was also obtained by the use of monoclonal or polyclonal antibodies and tryptic peptide maps. Five minor [GPIa, GPIc, GPIc*, GPIIa and GMP 140 (PADGEM)], as well as a major (GPIIIb) glycoprotein, were eluted at low salt concentrations. GPIIb-IIIa and GPIb were eluted at high salt concentrations. The N-terminal sequence of platelet GPIa was identical with that obtained by Takada & Hemler [(1989) J. Cell Biol. 109, 397-407]. However, the N-terminal sequence of platelet GPIc + Ic* and GPIIa were found to differ from those deduced from cDNA sequences isolated from human placenta or umbilical-vein endothelial-cell cDNA libraries. The combined use of f.p.l.c. and gas-phase sequencing techniques provides a very powerful tool to separate and characterize rapidly platelet or other cellular proteins for structural, immunological and functional studies.
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| 1956053 |
Isolation and structure of the cell growth inhibitory constituents from the western Pacific marine sponge Axinella sp |
10.1021/jm00115a027. |
J Med Chem |
Isolation and structure of the cell growth inhibitory constituents from the western Pacific marine sponge Axinella sp
Abstract
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| 1963473 |
Functional properties of a naturally occurring Trp1200----Ser1200 mutation of the insulin receptor |
10.1210/mend-4-8-1183. |
Mol Endocrinol |
Functional properties of a naturally occurring Trp1200----Ser1200 mutation of the insulin receptor
Abstract
- Based on the sequence of cDNA encoding the intracellular domain of the insulin receptor beta-subunit, we recently defined a heterozygous point mutation causing a Ser for Trp substitution at position 1200 in the tyrosine kinase domain of a patient (BI-2) with the type A syndrome of insulin resistance. We have now sequenced the remainder of BI-2's insulin receptor cDNA-coding region and find no additional alterations in the encoded proreceptor protein. The nucleotide sequence of cDNA encoding the portion of the beta-subunit which includes Trp1200 was normal in BI-2's unaffected mother. Hybridization of a mutant allele-specific oligonucleotide to polymerase chain reaction-amplified cDNA confirmed the presence of the mutant allele in the proband and excluded it in her unaffected sister and mother, 18 normal control subjects, and six other subjects with insulin resistance. To determine whether this mutation had functional consequences for receptor signalling, we reconstructed it into a full-length insulin receptor cDNA expression vector. Chinese hamster ovary cells were transfected with mutant cDNA, and the expressed insulin receptors were compared to receptors expressed by cells transfected with wild-type receptor cDNA. Both mutant and wild-type receptors were properly processed into receptor alpha- and beta-subunits, were expressed on the cell surface, and displayed similar insulin-binding affinity. In contrast, insulin-stimulated autophosphorylation of the mutant receptors was severely impaired, whether assessed in intact cells or with a partially purified receptor preparation.(ABSTRACT TRUNCATED AT 250 WORDS)
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| 1965061 |
omega-Conotoxin GVIA and nifedipine inhibit the depolarizing action of the fungal metabolite, destruxin B on muscle from the tobacco budworm (Heliothis virescens) |
10.1016/0041-0101(90)90090-t. |
Toxicon |
omega-Conotoxin GVIA and nifedipine inhibit the depolarizing action of the fungal metabolite, destruxin B on muscle from the tobacco budworm (Heliothis virescens)
Abstract
- Recent studies on a group of fungal metabolites, collectively called the destruxins, have suggested that these compounds activate calcium influx in insect skeletal muscle. In this study, we have investigated the sensitivity of destruxin B to the voltage-dependent calcium channel antagonists; omega-conotoxin GVIA, nifedipine, diltiazem and methoxyverapamil on skeletal muscle from the lepidopteran insect pest, tobacco budworm (Heliothis virescens). At a concentration of 1.7 microM, destruxin B caused a rapid decrease in the transmembrane resting potential. The effect of destruxin B on insect muscle was blocked by micromolar concentrations of omega-conotoxin GVIA and nifedipine but not by methoxyverapamil or diltiazem. The inhibitory activity of omega-conotoxin GVIA on invertebrate muscle tissue was surprising since this compound was previously thought to be selective to vertebrate nervous tissue. The sensitivity of the destruxin-stimulated depolarization to the two antagonists suggested that destruxin B activated a voltage-dependent calcium channel. Neuromuscular transmission was monitored in the presence of omega-conotoxin GVIA and nifedipine to investigate the physiological role of the destruxin-activated channel. Neither antagonist altered the waveform of graded action potentials produced by synaptic activation. The lack of effect of omega-conotoxin GVIA and a high dose of nifedipine could be explained by the existence of two populations of pharmacologically distinct voltage-dependent calcium channels on the muscle membrane. One population which is involved with the production of graded action potentials is insensitive to omega-conotoxin GVIA and nifedipine. The other population is activated by destruxin B and inhibited by omega-conotoxin GIVA and nifedipine.
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| 1969228 |
Human carboxypeptidase A identifies a BglII RFLP and maps to 7q31-qter |
None |
Am J Hum Genet |
Human carboxypeptidase A identifies a BglII RFLP and maps to 7q31-qter
Abstract
- A genomic clone for human carboxypeptidase has been isolated with a probe for rat CPA1 cDNA. A 1.7-kb HindIII/EcoRI fragment from the 3' flanking region of human carboxypeptidase detects a DNA polymorphism with BglIII. Multipoint linkage analysis with an established map of chromosome 7 markers shows that the most likely location of carboxypeptidase is at 7q31-qter, between D7S87 and D7S93. All other placements can be excluded with odds greater than 100:1. These and other markers confirm that carboxypeptidase lies distal to the locus for cystic fibrosis, at a distance of approximately 12 centimorgans. The regions containing identity to the rat gene were sequenced and shown to be 82% identical to exons 9 and 10 of the rat gene. The presence of a codon for isoleucine at the residues corresponding to codon 255 of rat CPA1 cDNA strongly suggests that the A form of human carboxypeptidase has been isolated.
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