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Biomedical subjects

B F Erlanger

Publications and source records attributed to B F Erlanger.

At least 91 records · Page 5Linked to original sources
PubMed1980

5-methylcytosine in the DNA of the polytene chromosomes of the diptera Sciara coprophila, Drosophila melanogaster and D. persimilis.

5-Methylcytosine has been detected in the DNA of the polytene chromosomes of Sciara coprophila, Drosophila melanogaster and D. persimilis, using specifically purified antibodies to 5-methylcytidine. The 5-methylcytosine is present in GC-rich sequences in the bands. Virtually no 5-methylcytosine is detectable in mitotic metaphase chromosomes of S. coprophila. Thus, methylation is associated with polytenization in these diptera. Restriction enzyme studies using HpaII, MspI, HhaI and AluI indicate that unmethylated 5'-CCGG-3', 5'-GCGC-3' and 5'-AGCT-3' sequences are abundant in polytene chromosome DNA. These sequences are probably not major sites of methylation. Since the DNA in the bands of polytene chromosomes is generally transcriptionally inactive, as well as extensively methylated, these results are consistent with the hypothesis that genes in the bands have been inactivated by a process involving DNA methylation.

5-Methylcytosine↗
PubMed1980

A covalently bound photoisomerizable agonist: comparison with reversibly bound agonists at Electrophorus electroplaques.

After disulphide bonds are reduced with dithiothreitol, trans-3- (alpha-bromomethyl)-3'-[alpha- (trimethylammonium)methyl]azobenzene (trans-QBr) alkylates a sulfhydryl group on receptors. The membrane conductance induced by this "tethered agonist" shares many properties with that induced by reversible agonists. Equilibrium conductance increases as the membrane potential is made more negative; the voltage sensitivity resembles that seen with 50 [mu]M carbachol. Voltage- jump relaxations follow an exponential time-course; the rate constants are about twice as large as those seen with 50 muM carbachol and have the same voltage and temperature sensitivity. With reversible agonists, the rate of channel opening increases with the frequency of agonist-receptor collisions: with tethered trans-Qbr, this rate depends only on intramolecular events. In comparison to the conductance induced by reversible agonists, the QBr-induced conductance is at least 10-fold less sensitive to competitive blockade by tubocurarine and roughly as sensitive to "open-channel blockade" bu QX-222. Light-flash experiments with tethered QBr resemble those with the reversible photoisomerizable agonist, 3,3',bis-[alpha-(trimethylammonium)methyl]azobenzene (Bis-Q): the conductance is increased by cis {arrow} trans photoisomerizations and decreased by trans {arrow} cis photoisomerizations. As with Bis-Q, ligh-flash relaxations have the same rate constant as voltage-jump relaxations. Receptors with tethered trans isomer. By comparing the agonist-induced conductance with the cis/tans ratio, we conclude that each channel's activation is determined by the configuration of a single tethered QBr molecule. The QBr-induced conductance shows slow decreases (time constant, several hundred milliseconds), which can be partially reversed by flashes. The similarities suggest that the same rate-limiting step governs the opening and closing of channels for both reversible and tethered agonists. Therefore, this step is probably not the initial encounter between agonist and receptor molecules.

Animals↗
PubMed1979

Conformational properties of the acetylcholine receptor as revealed by studies with constrained depolarizing ligands.

Conformational aspects of the acetylcholine receptor (AcChoR) of Electrophorus electricus have been examined by studies of its interaction with structurally related, constrained aromatic bis quaternary compounds. Among the compounds synthesized was 3,3'-bis[alpha-(trimethylammonium)-methyl]azobenzene dibromide (3,3'-bisQ). This compound is photochromic and can exist in a cis or trans isomeric form, both of which have now been isolated in pure form. Trans-3,3'-bisQ is the most potent activator known, producing a 60-mV depolarization at 0.2 muM and 50% activity at 0.06 muM. The cis isomer is less than 1% as active. Its high activity and constrained structure suggest that trans-3,3'-bisQ can be considered to be a "template" of the combining site of AcChoR, when the latter is in the activated state. The following conclusions can then be drawn concerning the AcChoR binding site. (i) Depolarization can occur by interaction with reagents that are essentially inflexible. (ii) The binding site has a planar hydrophobic region that interacts with methylene groups of acetylcholine and with hydrophobic areas in general. (iii) In the same plane as the hydrophobic area is a site that interacts with electron-donating functional groups including the carbonyl oxygen of acetylcholine and the azo nitrogens of trans-3,3'-bisQ. (iv) About 1.5 A out of the plane of the hydrophobic and the electron acceptor site is an anionic site; when the AcChoR is in the activated state, this site is separated from the electron acceptor site by 5.2 A and from another anionic site by 11 A. (v) The anionic sites are located within a cleft of limited size, sufficient to accommodate quaternary methyl groups. (vi) Although depolarization can occur with reagents that possess only hydrophobic and cationic groups if their geometric arrangement is proper, the highest activity resides in compounds capable of all of the interactions cited above.

Acetylcholine↗
PubMed1979

Isolation and characterization of rabbit anti-m7G-5'-P antibodies of high apparent affinity.

Antibodies highly specific for intact pm7G (7methylguanosine-5'-mono-phosphate) were induced by immunization of rabbits with a pm7G-BSA conjugate. Since the nucleotide is six-fold more stable than m7G (7-methylguanosine) to alkali-catalyzed fission of the imidazole ring, it is a more desirable antigen for obtaining antibodies capable of binding caps on eukaryotic mRNA. UV spectra demonstrated that the nucleotide in the conjugate was predominantly the intact form. Competition radioimmunoassay showed 1) high apparent affinities for pm7G, on the order of 10(-8)M, 2) low competition by the ring-opened form of the homologous hapten (*pm7G), and by m7G, 3) little or no competition by AMP, GMP, CMP, UMP or m6A, and 4) high apparent affinities for m7GpppAm, m7GpppN6MAm, m7GpppGm, m7GpppA.

Agglutination↗
PubMed1977

Preferential derivation of abnormal human G-group-like chromosomes from chromosome 15.

The marked binding of antibodies specific for 5-methylcytidine to the short arm of chromosome 15 distinguishes this chromosome from the other human acrocentrics. This method has been used to study over 60 individuals including 12 who did not have Down's syndrome, but who did have an extra G-group sized acrocentric chromosome. In six cases the extra chromosome did not show intensive binding of anti-5-methylcytidine. In the other six cases, the extra chromosome contained a 5-methylcytidine rich band at each end indicating that both ends were derived from chromosome 15 and contained centromeric heterochromatin normally present on the short arm of chromosome 15. The duplication of short arm material in the abnormal chromosomes was confirmed in all cases by quinacrine staining, nucleolar organizer (Ag-AS) staining or C-banding. In three cases, the abnormal chromosome appeared to arise from two different chromosomes 15. Several possible mechanisms for the production of the abnormal chromosome are discussed. The individuals with this abnormal chromosome all showed some degree of mental retardation, but few common physical findings.

Adult↗
PubMed1977

Peroxidase technique for the detection of photochemical lesions in intracellular deoxyribonucleic acid.

The widespread use of phototherapy for the prevention and treatment of neonatal hyperbilirubinemia has generated some conxern as physiologic substances other than bilirubin may be photoactivated. Little information is available on the long term toxicity of these photodecomposition products. Recent observations of the in vitro DNA-modifying activity of phototherapy lights has encouraged us to develop laboratory procedures which can identify and quantitate these light-induced alterations. The purpose of the present study was to develop a technique capable of detecting photochemical changes in the genetic material of human cells in tissue culture. The results demonstrate that the antinucleoside peroxidase staining procedure is capable of detecting changes in the DNA of human cells exposed to physiologic (riboflavin) and nonphysiologic (methylene blue) photosensitizing agents in the presence of light with a fluence rate (450 nm) of 141 muW-cm2.

Culture Techniques↗