The Excited States of Nucleic Acids

Eisinger, J.; Lamola, Angelo A.

doi:10.1007/978-1-4684-1878-1_5

Cited by 51 publications

(94 citation statements)

References 120 publications

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“…We observe that residual water in the specimen can quench nucleic acid fluorescence completely and protein fluorescence partially, the difference between the two cases lying perhaps in the fraction of fluorophors available for intimate association with water molecules. [At room temperature DNA is well known to be quenched in solution (2 A2, there will be about 100 useful excitations per destruction and even after multiplication by a so-far unknown fluorescent yield, 4F, we can expect a large number of emitted photons per destroyed fluorophor.…”

Section: Resultsmentioning

confidence: 99%

“…The electron effect is localizedindividual fluorescing groups (or fluorophors), such as the tryptophan and tyrosine residues of protein (1), or the bases of nucleic acids (2), or fluorescein (3), are excited mainly within a distance of 20 A or so from the beam (4 We show that the fluorescence of nucleic acids in particular is sufficiently long-lived that pictures of nucleic-acid dis- § To whom correspondence should be addressed. tribution in situ will be possible at a resolution approaching the theoretical limit of 20 A.…”

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confidence: 99%

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Identification of biological molecules in situ at high resolution via the fluorescence excited by a scanning electron beam.

Hough¹,

McKinney²,

Ledbeter³

et al. 1976

Proc. Natl. Acad. Sci. U.S.A.

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Proteins, nucleic acids, and fluorescein-conjugated antibody are shown to be identifiable in situ via the fluorescence excited by the focused electron beam of a scanning electron microscope. A molecular species is identified by its characteristic fluorescence spectrum and by a characteristic alteration of the spectrum with time under the electron beam. Primary protein fluorescence is relatively rapidly destroyed by the beam, but protein photoproduct fluorescence is more rugged and will in some cases permit detection of small numbers of protein molecules. Nucleic acid fluorescence is extremely long-lived and will permit detection of small numbers of nucleic acid residues. The theoretical resolution limit for localization of a particular molecular speciesabout 20 A-is determined by the known maximum distance for molecular excitation by fast electrons. Direct extrapolation from an observed resolution of 900 A in the localization of nucleic acid using a low-efficiency detector leads to an experimental resolution limit of less than 60 A. Fluorescence is strongly quenched by residual water in the specimen. Similar quenching is produced by some macromolecular associations and so may serve to localize such associations.The fluorescence of proteins, nucleic acids, and fluoresceincoupled antibody are excited not only by ultraviolet light, but also by fast electrons. The electron effect is localizedindividual fluorescing groups (or fluorophors), such as the tryptophan and tyrosine residues of protein (1) MATERIALS AND METHODS Scanning Electron Microscope. The microscope used in this work is the AMR 1000 (Advanced Metals Research Corporation, Waltham, Mass.). The electron source is thermionic, and high vacuum is provided by an oil diffusion pump with liquid nitrogen trap. Light from the microscope filament normally gives a serious background for the photon detector used to detect fluorescence; the background is reduced by misaligning the filament mechanically and restoring a portion of the lost beam current by adjustment of the electromagnetic alignment currents. The measurements reported below were made at 20 kV accelerating voltage. Beam currents on target ranged from 5 X 10-13 amp (= 3 X 106 electrons/sec) to 1 X 10-9 amp ( = 6 X 109 electrons/ sec). The specimen-support stub was maintained at room temperature (220).Photon Detector. An aluminum mirror in the shape of a half-paraboloid (6) with axis horizontal covers the specimen. The electron beam of the microscope traverses a vertical hole in the mirror and intersects the specimen at the focus of the paraboloid. Fluorescent light collected by the mirror is passed to a Pyrex tube, aluminized on the inside, which conducts it to a quartz window at the wall of the vacuum chamber. Outside, the light is dispersed by a Jarrell-Ash 0.25 m grating monochromator and a selected wavelength band is detected by an EMI 9789QB bi-alkali photomultiplier tube placed at the exit slit. The complete light collection and detector system has an overall theoretical efficiency of 2%, bu...

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Identification of biological molecules in situ at high resolution via the fluorescence excited by a scanning electron beam.

Hough¹,

McKinney²,

Ledbeter³

et al. 1976

Proc. Natl. Acad. Sci. U.S.A.

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“…Reports on oxygen sensitivity of lanthanide ion emission are scarce. An oxygen-sensitive emission of Eu3+ in the presence of tryptophan has been reported [7].…”

Section: Discussionmentioning

confidence: 99%

The replacement of calcium by terbium as an allosteric effector of hemocyanins

Kuiper¹,

Agró²,

Antonini³

et al. 1979

FEBS Letters

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“…4), where the lifetime is approximately a microsecond [23]. Triplet state energies are much lower than the singlets and their relative energies are different, so T is now lower than C [24]. In DNA, triplet energies (measured as T- and C-containing CPDs plus apurinic sites [25], hence labeled “N”) appear to be even lower than in free bases or nucleotides [24].…”

Section: Cpds From Photonsmentioning

confidence: 99%

Chemical excitation of electrons: A dark path to melanoma

Premi

Brash

2016

DNA Repair

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Sunlight’s ultraviolet wavelengths induce cyclobutane pyrimidine dimers (CPDs), which then cause mutations that lead to melanoma or to cancers of skin keratinocytes. In pigmented melanocytes, we found that CPDs arise both instantaneously and for hours after UV exposure ends. Remarkably, the CPDs arising in the dark originate by a novel pathway that resembles bioluminescence but does not end in light: First, UV activates the enzymes nitric oxide synthase (NOS) and NADPH oxidase (NOX), which generate the radicals nitric oxide (NO•) and superoxide (O2•−); these combine to form the powerful oxidant peroxynitrite (ONOO−). A fragment of the skin pigment melanin is then oxidized, exciting an electron to an energy level so high that it is rarely seen in biology. This process of chemically exciting electrons, termed “chemiexcitation”, is used by fireflies to generate light but it had never been seen in mammalian cells. In melanocytes, the energy transfers radiationlessly to DNA, inducing CPDs. Chemiexcitation is a new source of genome instability, and it calls attention to endogenous mechanisms of genome maintenance that prevent electronic excitation or dissipate the energy of excited states. Chemiexcitation may also trigger pathogenesis in internal tissues because the same chemistry should arise wherever superoxide and nitric oxide arise near cells that contain melanin.

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The Excited States of Nucleic Acids

Cited by 51 publications

References 120 publications

Identification of biological molecules in situ at high resolution via the fluorescence excited by a scanning electron beam.

Identification of biological molecules in situ at high resolution via the fluorescence excited by a scanning electron beam.

The replacement of calcium by terbium as an allosteric effector of hemocyanins

Chemical excitation of electrons: A dark path to melanoma

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