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Biomedical subjects

M J Waring

Publications and source records attributed to M J Waring.

At least 145 records · Page 8Linked to original sources
PubMed1981

Kinetics of dissociation of quinoxaline antibiotics from DNA.

The kinetics of detergent-induced dissociation of triostins A and C and quinomycin C from DNA have been investigated. All three antibiotics dissociate from poly(dA-dT) and poly(dG-dC) in a simple first-order fashion whereas their dissociation from a natural DNA (calf thymus) is complex, requiring three exponential terms for its complete description. This behaviour is attributed to sequence-selectivity on the part of the drugs and seems to represent dissociation from different classes of intercalative binding site. The time constants of dissociation are better resolved for quinomycins than for triostins, consistent with the view that quinomycins are more sequence-specific in their interaction with DNA, but it is not possible to identify any class of binding site with the alternating purine-pyrimidine sequences of the synthetic polydeoxynucleotides. In general, the triostins dissociate an order of magnitude faster than the corresponding quinomycins. This is attributable to a larger entropy of activation, presumably reflecting greater flexibility of the octapeptide ring when the cross-bridge is a disulphide as opposed to the slightly shorter thioacetal found in quinomycins. The longest time constant in the dissociation of each of the four quinoxaline antibiotics from calf thymus DNA correlates well with its antibacterial potency, in agreement with the conclusion that the biological effects result from impairment of the role of DNA as a template for polymerase activity.

Animals↗
PubMed1980

Effects of ring substituents and linker chains on the bifunctional intercalation of diacridines into deoxyribonucleic acid.

Sedimentation experiments with closed circular duplex PM2 deoxyribonucleic acid (DNA) and viscosity measurements with sonicated rodlike DNA fragments have been performed to investigate unwinding and extension of the DNA helix associated with binding of homologous series of diacridines. When the acridine nuclei are linked via 9-amino substituents with chains permitting interchromophore separation in the critical region between 8.8 and 11.3 A, it is found that substituents at positions 2, 3, and 6 restrict bifunctional intercalation to compounds capable of sandwiching at least two base pairs in the intercalated complex. Unsubstituted diacridines, and derivatives bearing an ethyl group at position 4, can bis-intercalate with a significantly shorter linking chain. The presence of amino groups in the linker does not affect the ability to bis-intercalate but increases the helix unwinding angle by 30--40% and decreases the helix extension per bound ligand molecule by 11--18%. Bifunctional reaction is observed with a diacridine linked via the 4--4' positions showing that 9-aminoacridine can intercalate in at least two major orientations with the 9 or 10 position directed toward the helix axis. Both orientations can be accommodated simultaneously within a single diacridine linked via the 9--4' positions with a bridge sufficiently long to encompass two base pairs. An acridone substituted at positions 4 and 5 with positively charged side chains intercalates with a helix unwinding angle indistinguishable from that of ethidium whereas an uncharged bisacridone failed to yield a detectable complex with DNA. Tilorone dihydrochloride, a structurally similar antiviral drug, was found to intercalate with an unwinding angle approximately half that of ethidium. The potentially bifunctional bisquinoline drug dequalinium causes relaxation of the supercoiling of PM2 DNA but probably not by simultaneous intercalation of both its chromophores.

Acridines↗
PubMed1980

Binding of quinoline analogues of echinomycin to deoxyribonucleic acid. Role of the chromophores.

Two novel antibiotics were isolated, designated compounds 1QN and 2QN respectively, having quinoline rings in place of one or both of the quinoxaline chromophores of echinomycin. Each removes and reverses the supercoiling of closed circular duplex DNA from bacteriophage PM2 in the fashion characteristic of intercalating drugs. For compound 1QN, the unwinding angle at I0.01 is almost twice that of ethidium, whereas for compound 2QN the value is indistinguishable from that of ethidium. Binding of both analogues produced changes in the viscosity of sonicated rod-like DNA fragments corresponding to double the helix extension found with ethidium, a feature characteristic of bifunctional intercalation by quinoxaline antibiotics. These results suggest that both compounds 1QN and 2QN behave as bifunctional intercalators but that compound 2QN produces only half the helix unwinding seen with compound 1QN and the natural quinoxalines. Binding curves for the interaction of both analogues with a variety of synthetic and naturally occurring nucleic acids were determined by solvent-partition analysis. Values for compound 2QN were also obtained by a fluorimetric method and found to agree well with the solvent-partition measurements. Compound 1QN bound most tightly to Micrococcus lysodeikticus DNA and, like echinomycin, exhibited a broad preference for (G + C)-rich DNA species. For compound 2QN no marked (G + C) preference was indicated, and the tightest binding among the natural DNA species studied was found with DNA from Escherichia coli. The two analogues also displayed different patterns of specificity in their interaction with synthetic nucleic acids. Compound 2QN bound to poly(dA-dT) slightly more tightly than to poly-(dG-dC), whereas compound 1QN displayed a large (approx. 11-fold) preference in the opposite sense. There was evidence of co-operativity in the binding to poly(dA-dT). It may be concluded that the chromophore moieties play an active role in determining the capacity of quinomycin antibiotics to recognize and bind selectively to specific sequences in DNA.

Base Composition↗
PubMed1980

Interaction between synthetic analogues of quinoxaline antibiotics and nucleic acids: role of the disulphide cross-bridge and D-amino acid centres in des-N-tetramethyl-triostin A.

1 [Ala3, Ala7] TANDEM is an analogue of des-N-tetramethyl-triostin A (TANDEM) in which both L-Cys residues of the octapeptide ring are replaced by L-Ala; accordingly it lacks the disulphide cross-bridge which limits the conformational flexibility of TANDEM. 2 In [L-Ser1] TANDEM the configuration of one of the serine residues is inverted, altering the disposition of one of the quinoxaline chromophores with respect to the peptide ring. 3 Both compounds interact weakly but detectably with natural DNAs as judged by spectral shifts and increases in the thermal denaturation ('melting') temperature Tm. They also raise the Tm of poly rA . poly rU. 4 Binding isotherms determined by solvent partition analysis with [Ala3, Ala7] TANDEM yield association constants of about 10(3) M-1 for its interaction with natural DNAs. A Scatchard plot for binding to poly(dA-dT) determined by solvent partition and spectrophotometric methods shows marked evidence of cooperativity with an intrinsic association constant 1.9 x 10(4) M-1, 8.7 nucleotides per binding site, and cooperativity parameter 15. 5 Binding of [Ala3, Ala7] TANDEM to short rod-like fragments of poly(dA-dT) increases their contour length by almost the theoretical amount expected for an ideal process of bifunctional intercalation. 6 No effect of either compound on the winding of the DNA helix could be detected in sedimentation experiments with closed circular duplex PM2 DNA. 7 It is concluded that the cross-bridge of TANDEM greatly stabilizes its binding to DNA, most probably via entropic factors, but is not the only structural feature that influences its AT sequence-selectivity. The consequences of epimerising one of the D-Ser residues appear as disastrous as epimerising both. 8 The experimental details for the synthesis of [Ala3, Ala7] TANDEM and [L-Ser1] TANDEM are given in an appendix to this paper.

Amino Acids↗
PubMed1979

Intercalative binding to DNA of antitumour drugs derived from 3-nitro-1,8-naphthalic acid.

Two new antitumour drugs, imide derivatives of 3-nitro-1,8-naphthalic acid having different basic side chains linked to the imide nitrogen, have been shown to bind to double-helical DNA by intercalation. At ionic strength 0.01 mol/litre, pH 7, their intrinsic association constants are about 1.45 x 10(5) M-1 and each bound ligand molecule occludes about 3.4 nucleotides of the DNA lattice. They remove and reverse the supercoiling of closed circular duplex PM2 DNA with apparent unwinding angles of 11-12 degrees per bound drug molecule, referred to an assumed unwinding angle of 26 degrees for ethidium. They increase the viscosity of sonicated rod-like DNA fragments, each bound drug molecule producing a calculated increment in length of 2.2 - 2.5 A. No important differences between the DNA-binding characteristics of the two drugs were detected, though one appears marginally more active than the other in certain biological tests.

Animals↗
PubMed1978

Structural limitations on the bifunctional intercalation of diacridines into DNA.

An homologous series of diacridines containing two 9-aminoacridine chromophores linked via a simple methylene chain has been studied in order to investigate the minimum interchromophore separation required to permit bifunctional intercalation. Viscometric, sedimentation, and electric dichroism experiments show that compounds having one to four methylene groups in the linker are restricted to monofunctional intercalation, whereas the interaction becomes bifunctional when the chain length is increased to six carbons or more. The results indicate that bifunctional reaction occurs with an interchromophore distance not exceeding 8.8 A, implying that intercalation by these compounds is not subject to neighbor exclusion if the mode of binding is of the classical intercalation type.

Acridines↗
PubMed1978

A serological survey on the prevalence of infectious bovine rhinotracheitis in Buckinghamshire, Berkshire and Oxfordshire.

Of the 2368 cattle sera from herds in Buckinghamshire, Berkshire and Oxfordshire examined for infectious bovine rhinotracheitis antibody by an indirect haemagglutination test, 162 (6.8 per cent) proved positive. Positive titres were more prevalent in older cows and they tended to show higher titres. There was little evidence of infection in the bulls tested. The percentage of positive animals in Berkshire and Oxfordshire was 4.7 compared with 10.5 in Buckinghamshire. The infection was not known to be associated with any clinical disease.

Animals↗
PubMed1978

Bifunctional intercalation and sequence specificity in the binding of quinomycin and triostin antibiotics to deoxyribonucleic acid.

Quinomycin C, triostin A and triostin C are peptide antibiotics of the quinoxaline family, of which echinomycin (quinomycin A) is also a member. They all remove and reverse the supercoiling of closed circular duplex DNA from bacteriophage PM2 in the fashion characteristic of intercalating drugs, and the unwinding angle at I 0.01 is, in all cases, almost twice that of ethidium. Thus, as with echinomycin, they can be characterized as bifunctional intercalating agents. For the triostins this conclusion has been confirmed by measurements of changes in the viscosity of sonicated rod-like DNA fragments; the helix extension was found to be almost double that expected for a simple monofunctional intercalation process. For triostin A, further evidence for bifunctionality was derived from the cross-over point of binding isotherms to nicked circular and closed circular bacteriophage-PM2DNA. Binding curves for the interaction of quinomycin C and triostin A with a variety of synthetic and naturally occurring nucleic acids were determined by solvent-partition analysis, but triostin C was too insoluble in aqueous solution to make this method applicable. For quinomycin C the highest binding constant was found with Micrococcus lysodeikticus DNA, and its pattern of specificity among natural DNA species was broadly similar to that of echinomycin, although the binding constants were 2--6 times as large. For triostin A the highest binding constant was again found for M. lysodeikticus DNA, but the specificity pattern was quite different from that of the quinomycins. In particular, triostin A bound better to poly(dA-dT) than to the poly(dG-dC) whereas this order was reversed for quinomycin C. There was also evidence that the binding to poly(dA-dT) might be co-operative in nature. No significant interaction could be detected with poly(dA).poly(dT) or with RNA from Escherichia coli. Poly(dG).poly(dC) gave variable results, depending on the source of the polymer. The different patterns of specificity displayed by the quinomycins and triostins are tentatively ascribed to differences in their conformations in solution.

Anti-Bacterial Agents↗
PubMed1978

Interaction between synthetic analogues of quinoxaline antibiotics and nucleic acids. Changes in mechanism and specificity related to structural alterations.

The interaction with DNA of six chemically synthesized derivatives of the quinoxaline antibiotics was investigated. Five of the compounds bound only weakly to DNA or not at all; for these substances spectrophotometric measurements, sedimentation studies with closed circular duplex bacteriophage-PM2 DNA and thermal-denaturation profiles were used to determine limits fot the binding constants. No interaction could be detected with two products of degradation of echinomycin (quinomycin A), one of which, echinomycinic acid dimethyl ester, had the lactone linkages opened, whereas the other retained an intact octapeptide ring but had a broken cross-bridge. The other compounds studied were des-N-tetramethyl-triostin A ('TANDEM') and its derivatives. A derivative of 'TANDEM' IN WHICH benzyloxycarbonyl moieties replace both quinoxaline chromophores had binding constants to nucelic acids in the range 10(2)--10(3)-1, whereas no interaction could be detected for a benzyloxycarbonyl derivative that, in addition, had the cross-bridge broken. The derivative of 'TANDEM' with L-serine in place of D-serine in both positions showed no detectable interaction with Clostridium perfringens DNA, whereas the binding constant to poly(dA-dT) was approx 2 X 10(3)M-1. 'TANDEM' itself bound strongly to DNA, and the bathochromic and hypochromic shifts in its u.v.-absorption spectrum in the presence of DNA were similar to those seen with echinomycin. From the effect on the sedimentation coefficient of closed circular duplex bacteriophage-PM2 DNA the mechanism of binding was shown to involve bifunctional intercalation, typical of the naturally occurring quinoxaline antibiotics. Solvent-partition analysis was used to determine binding constants for the interaction between 'TANDEM' and a variety of natural and synthetic DNA species. The pattern of specificity thus revealed differed markedly from that previously found with the naturally occurring quinoxaline antibiotics. Most striking was the evident large preference for (A + T)-rich DNA species, in complete contrast with echinomycin and triostin A. The highest binding constant was found for poly(dA-dT), the interaction with which appeared highly co-operative in character. The conformations adopted by those quinoxaline compounds that bind strongly to DNA were examined withe aid of molecular models on the basis of results derived from n.m.r. and computer studies. It appears that the observed patterns of base-sequence specificity are determined, at least in part, by the structure and conformation of the sulphur-containing cross-bridge.

Anti-Bacterial Agents↗