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G Payne

Publications and source records attributed to G Payne.

50 records · Page 3Linked to original sources
PubMed1988

Techniques for improving orthodontic results in the treatment of missing maxillary lateral incisors. A case report with literature review.

We have presented a case report of the orthodontic treatment of a patient with congenitally missing lateral incisors and with skeletal and dental deep bite. Information was provided on methods to improve clinical orthodontic results. Different sections deal with (1) various diagnostic criteria for the best treatment approach, (2) variations in maxillary arch wire manipulation, (3) biomechanical considerations, (4) modifications of clinical crown by special procedures so that the canines resemble and function as lateral incisors, (5) functional considerations of the occlusion, and (6) details in finishing. Particular emphasis was placed on the use of a special design of closing loops for simultaneous space closure and intrusion of the anterior teeth. This article has discussed the principles of incisor and canine intrusion, and has demonstrated that the closing loops described are capable of intruding incisors with minimal side effects on the posterior teeth. It has also demonstrated how control of the mechanical variables dramatically increased the efficiency and effectiveness of intra- and extraoral forces in the treatment of malocclusion.

Adolescent↗
PubMed1988

Identification of the second chromophore of Escherichia coli and yeast DNA photolyases as 5,10-methenyltetrahydrofolate.

Denaturation of DNA photolyase (deoxyribodipyrimidine photolyase, EC 4.1.99.3) from Escherichia coli with guanidine hydrochloride or acidification to pH 2 released, in addition to FAD, a chromophore with the spectral and chromatographic properties of a reduced pterin. Treatment of the enzyme with iodine prior to acidification converted the chromophore to a stable, oxidized derivative, which was resolved by HPLC into four species with identical spectral properties. The same species, in the same distribution, were obtained from the yeast enzyme. The material isolated from the iodine-oxidized enzyme was shown to be a pterin by conversion to pterin-6-carboxylic acid with alkaline permanganate and was found to release glutamate upon acid hydrolysis. The presence of 10-formylfolate in the isolated, oxidized chromophore was demonstrated by absorption and fluorescence spectroscopy and by deformylation and conversion to folic acid. Analysis of the distribution of polyglutamates revealed that the four species identified by HPLC corresponded to the tri-, tetra-, penta-, and hexaglutamate derivatives of 10-formylfolate. The results were consistent with gamma linkages in the triglutamate derivative with additional glutamates linked via the alpha-carboxyl group of the preceding residue. Treatment with rat plasma hydrolase produced the monoglutamate derivative of 10-formylfolate. The native, enzyme-bound form of the folate cofactor was identified as 5,10-methenyltetrahydrofolylpolyglutamate by effecting release and isolation at low pH to protect the 5,10-methenyl bridge and preserve the reduced pyrazine ring structure.

Bacterial Proteins↗
PubMed1987

The active form of Escherichia coli DNA photolyase contains a fully reduced flavin and not a flavin radical, both in vivo and in vitro.

Escherichia coli DNA photolyase is a flavoprotein that when purified is blue in color and contains a stable neutral radical FAD (E-FADH). In the presence of a suitable electron donor (i.e., thiols, tyrosine, or NADH) the radical FAD adsorbs visible light and undergoes photoreduction to the fully reduced FAD (E-FADH2). The in vitro quantum yield of dimer repair for E-FADH is 0.07 while that of E-FADH2 approaches the in vivo value of 1. Electron paramagnetic resonance studies on whole cells indicate that the in vivo form of photolyase is E-FADH2 with enzyme containing radical FAD generated predominantly during the ammonium sulfate precipitation step of the purification. Activity measurements of E-FADH using long-wavelength photoreactivating light indicate that enzyme containing FAD in the radical form is not active in dimer repair. Dimer repair observed with E-FADH at shorter wavelengths is probably photoreduction of E-FADH followed by dimer repair by E-FADH2.

Deoxyribodipyrimidine Photo-Lyase↗
PubMed1987

Photochemical properties of Escherichia coli DNA photolyase: selective photodecomposition of the second chromophore.

Escherichia coli DNA photolyase contains a stable flavin radical and a second chromophore (SC) of unknown structure. The effects of flash (both conventional and laser) excitation of either the radical alone or both the radical and the second chromophore have been investigated by variation of the excitation wavelengths. Radical excitation leads to an electron abstraction by the lowest excited doublet state of the radical from an amino acid residue, probably a cysteine or tyrosine. On a longer time scale, a back-reaction occurs that can be prevented by the presence of certain electron donors, e.g., thiols, NADH, or tyrosine, but not pyrimidine dimers. Excitation of the second chromophore leads to electronic energy transfer from second chromophore excited states to the ground-state flavin radical doublet state, thus increasing the population of the lowest excited doublet state. Repetitive excitation of the enzyme with white light leads to photodecomposition of the second chromophore but not of the flavin adenine dinucleotide cofactor. Enzyme with photodecomposed SC retains full activity.

Deoxyribodipyrimidine Photo-Lyase↗
PubMed1987

Action mechanism of Escherichia coli DNA photolyase. I. Formation of the enzyme-substrate complex.

Escherichia coli DNA photolyase (photoreactivating enzyme) is a flavoprotein. The enzyme binds to DNA containing pyrimidine dimers in a light-independent step and, upon illumination with 300-600 nm radiation, catalyzes the photosensitized cleavage of the cyclobutane ring thus restoring the integrity of the DNA. We have studied the binding reaction using the techniques of nitrocellulose filter binding and flash photolysis. The enzyme binds to dimer-containing DNA with an association rate constant k1 estimated by two different methods to be 1.4 X 10(6) to 4.2 X 10(6) M-1 S-1. The dissociation of the enzyme from dimer-containing DNA displays biphasic kinetics; for the rapidly dissociating class of complexes k2 = 2-3 X 10(-2) S-1, while for the more slowly dissociating class k2 = 1.3 X 10(-3) to 6 X 10(-4) S-1. The equilibrium association constant KA, as determined by the nitrocellulose filter binding assay and the flash photolysis assay, was 4.7 X 10(7) to 6 X 10(7) M-1, in reasonable agreement with the values predicted from k1 and k2. From the dependence of the association constant on ionic strength we conclude that the enzyme contacts no more than two phosphodiester bonds upon binding; this strongly suggests that the pyrimidine dimer is the main structural determinant of specific photolyase-DNA interaction and that nonspecific ionic interactions do not contribute significantly to substrate binding.

Collodion↗
PubMed1987

Action mechanism of Escherichia coli DNA photolyase. III. Photolysis of the enzyme-substrate complex and the absolute action spectrum.

The absolute action spectrum of Escherichia coli DNA photolyase was determined in vitro. In vivo the photoreactivation cross-section (epsilon phi) is 2.4 X 10(4) M-1 cm-1 suggesting that the quantum yield (phi) is about 1.0 if one assumes that the enzyme has the same spectral properties (e.g. epsilon 384 = 1.8 X 10(4) M-1 cm-1) in vivo as those of the enzyme purified to homogeneity. The relative action spectrum of the pure enzyme (blue enzyme that contains FAD neutral semiquinone radical) agrees with the relative action spectrum for photoreactivation of E. coli, having lambda max = 384 nm. However, the absolute action spectrum of the blue enzyme yields a photoreactivation cross-section (epsilon phi = 1.2 X 10(3) at 384 nm) that is 20-fold lower than the in vivo values indicative of an apparent lower quantum yield (phi approximately equal to 0.07) in vitro. Reducing the enzyme with dithionite results in reduction of the flavin semiquinone and a concomitant 12-15-fold increase in the quantum yield. These results suggest that the flavin cofactor of the enzyme is fully reduced in vivo and that, upon absorption of a single photon in the 300-500 nm range, the photolyase chromophore (which consists of reduced FAD plus the second chromophore) donates an electron to the pyrimidine dimer causing its reversal to two pyrimidines. The reduced chromophore is regenerated at the end of the photochemical step thus enabling the enzyme to act catalytically.+

DNA↗
PubMed1984

Proviral deletions and oncogene base-substitutions in insertionally mutagenized c-myc alleles may contribute to the progression of avian bursal tumors.

Bursal lymphomas induced in chickens by avian leukosis viruses (ALVs) harbor proviral insertions that augment expression of an adjacent cellular oncogene, c-myc. To analyze such insertionally mutagenized c-myc genes in greater detail, we isolated molecular clones from two independent tumors. Precise proviral integration has occurred within the transcribed region of the c-myc gene in both mutant alleles. The proviruses bear different internal deletions that preclude the expression of the gag, pol, and env genes. The c-myc gene from bursal lymphoma LL4 contains a single copy of an ALV long terminal repeat (LTR), presumably the product of homologous recombination between LTRs at the ends of a normal provirus; the "solo" LTR is positioned in the correct orientation to act as a promoter for the c-myc gene. Bursal lymphoma LL3 contains an ALV provirus positioned upstream in the opposite transcriptional orientation to the coding exons of c-myc and deleted from a site within the leader region into the gag gene. In addition, the nucleotide sequence of the c-myc gene from tumor LL3 differs from the published sequence of the normal c-myc coding region at 3 positions of 180 determined. One of these changes, a silent nucleotide transition, is documented as a somatic mutation by restriction endonuclease mapping. It is flanked by two other candidate tumor-specific point mutations, one of which predicts an amino acid replacement, Pro----Thr at position 63. Thus, additional lesions that may affect the expression of viral genes and the quantity and nature of the putative c-myc gene product occur in provirally mutated c-myc alleles and may contribute to tumor progression.

Alleles↗
PubMed1981

The isolation of a field strain of Haemonchus contortus in Queensland showing multiple anthelmintic resistance.

Following the apparent failure of levamisole to control infections of Haemonchus contortus in sheep at Lawes in south eastern Queensland, a strain of this parasite was isolated at the Animal Research Institute, Yeerongpilly. This strain was used to infect sheep at Yeerongpilly and the Merrindale Research Station, Victoria where four experiments to classify the resistance pattern of the parasite were carried out. Resistance to thiabendazole was first suspected in 1969, and these experiments confirmed that resistance to this drug was still present. They also showed that a strong degree of resistance had been developed to both levamisole and morantel tartrate. Other benzimidazole anthelmintics and also the organophosphorus compound naphthalophos were only moderately effective against the original isolate but rafoxanide, nitroxynil and phenothiazine were almost 100% effective. Other highly effective chemicals were disophenol and closantel. After passaging the strain for four generations with both levamisole and albendazole, resistance to both naphthalophos and the newer benzimidazole anthelmintics increased dramatically. This is the first report of a field strain of H. contortus exhibiting resistance to benzimidazole, non-benzimidazole and organophosphorus anthelmintics.

Albendazole↗
PubMed1980

A Comparison of Purified Host Specific Toxin from Helminthosporium maydis, Race T, and Its Acetate Derivative on Oxidation by Mitochondria from Susceptible and Resistant Plants.

NADH or succinate oxidation and malate oxidation were differentially affected in mitochondria from both susceptible and resistant corn by a purified and chemically characterized preparation of host-specific toxin from Bipolaris (Helminthosporium) maydis, race T. NADH and succinate oxidation by susceptible T corn mitochondria were stimulated 50 to 200% with apparent uncoupling from the cytochrome chain at approximately 10(-9)m toxin (5 to 20 ng/ml). Significant inhibition of malate oxidation was observed at slightly higher toxin concentrations, but oxidation was still coupled to ADP utilization. Inhibition of malate oxidation also was observed in N corn (resistant) and soybean mitochondria at approximately 1,000-fold greater concentrations, but stimulation of NADH and succinate oxidation was not found at any toxin concentration tested.A fully acetylated toxin derivative at approximately 1 microgram per milliliter also caused stimulation of NADH or succinate oxidation in T corn mitochondria, but not those of N corn or soybean mitochondria at 100 micrograms per milliliter. Malate oxidation was inhibited to the same extent by toxin acetate with mitochondria from T corn, N corn, and soybean. The blocking of hydroxyl groups in race T toxin by acetyl functions eliminated selectivity toward malate oxidation only. The data suggest that inhibition of malate oxidation is either a separate or secondary effect of selective action of toxin on T corn mitochondria, perhaps by interference with transport in or out of the matrix. Sensitivity of T, but not N, corn mitochondria to purified toxin decays within minutes after pellets are suspended in aqueous osmotica, with no obvious change in mitochondrial integrity. The action of race T toxin seems to involve a labile process, such as ion gradient(s), or an unstable structural conformation of T corn mitochondria.

Journal Article↗