Universal computer interface for the Cary 118C spectrophotometer

Sutherland, John C.; Boles, Thomas T.

doi:10.1063/1.1135628

Cited by 17 publications

(9 citation statements)

References 7 publications

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“…Absorption spectra were recorded with a Cary 118C absorption spectrometer (Varian Associates, Palo Alto, CA) equipped with a scattered-transmission accessory (model 1862000). Operation of the spectrometer was controlled by a computer (model 4051, Tektronix Inc., Beaverton, OR) via an interface which has been described elsewhere (7). The computer advanced the wavelength drive of the spectrometer from one wavelength to the next, typically 1 nm, and averaged absorbance values until the standard deviation of the absorbance was less than 0.001 optical density unit.…”

Section: Dnas From Calf Thymus Clostridium Perfringens Escherichia mentioning

confidence: 99%

Absorption Spectrum of DNA for Wavelengths Greater than 300 nm

1981

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Section: Dnas From Calf Thymus Clostridium Perfringens Escherichia mentioning

confidence: 99%

Absorption Spectrum of DNA for Wavelengths Greater than 300 nm

1981

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“…Absorption spectra were recorded with a Cary 118C spectrophotometer (Varian, Palo Alto, CA) operated under computer control (20). CD spectra were recorded with the Synchrotron Ultraviolet Project spectrometer operating at the National Bureau of Standards synchrotron storage ring (Gaithersburg, MD).…”

Section: Methodsmentioning

confidence: 99%

Z-DNA: vacuum ultraviolet circular dichroism.

Sutherland¹,

Griffin²,

Keck³

et al. 1981

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

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In concentrated salt or ethanolic solutions, the self-complementary copolymer poly(dG-dC)-poly(dG-dC) forms a left-handed double-helical structure that has been termed "Z-DNA." The first evidence for this structure came from changes observed in the circular dichroism (CD) spectrum between 230 and 300 nm for low-and high-salt solutions (Pohl, F. M. & Jovin, T. M. (1972)J. MoL BioL 67,. In 3 M NaCl, the CD spectrum is approximately inverted compared to the B-form spectrum observed in low-salt solution. We measured the vacuum ultraviolet CD spectrum of poly(dG-dC)poly(dG-dC) down to 180 nm under conditions in which the 230-to 300-nm spectrum is inverted. Below 200 nm, where the B form exhibits the large positive peak at 187 nm that is characteristic ofright-handed double-helical DNAs, the Z form exhibits a large negative peak at 194 nm and a positive band below 186 nm. Therefore, the Z-form vacuum ultraviolet CD spectrum resembles an inverted and red-shifted B-form spectrum. The magnitudes ofthe differences observed between the B and Z forms in the CD spectrum below 200 nm are about 10 times greater than those observed between 230 and 300 nm. The vacuum ultraviolet CD spectrum of poly(dG-dC)-poly(dG-dC) in 3 M Cs2SO4 also is inverted compared to the B-form spectrum; however, between 230 and 300 nm, it is nonconservative with a negative maximum at 290 nm and a weak positive CD signal above 300 nm, presumably reflecting differential light scattering and indicating the existence of molecular aggregates. Our results suggest that the vacuum ultraviolet CD spectrum is sensitive to the handedness of doublehelical DNA structures. The CD spectrum in this region should complement other spectroscopic methods in relating the structures of poly(dG-dC)poly(dG-dC) existing in solution to those determined in the solid state by x-ray crystallography.The first indications of the existence of the Z form of DNA were the dramatic changes in the 230-to 300-nm circular dichroism (CD) spectrum ofthe copolymer poly(dG-dC)-poly(dG-dC) produced by increasing salt concentrations (1). In low concentrations ofNaCl, the 230-to 300-nm CD spectrum is approximately conservative, with a positive peak near 275 nm and a negative peak near 253 nm, resembling the spectrum of B-form DNA. As the concentration of NaCl is increased, a cooperative transition with a midpoint at about 2.5 M NaCl leads to an inverted CD spectrum with a negative maximum near 292 nm and a positive maximum near 265 nm.The dramatic spectral changes caused by high salt (1-5) prompted several x-ray diffraction investigations (6-8) of the three-dimensional structure ofcrvstals ofshort, defined lengths of dG-dC oligomers and led to the discovery of what is now called Z-DNA, a zig-zag, left-handed helix in which the guanine residues adopt a syn conformation relative to the glycosidic bond. Fiber diffraction patterns of much longer chains of poly(dG-dC)'poly(dG-dC) have been interpreted as having a similar conformation (9). Crystallographic studies show that more than one fo...

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“…Information about the ironsulfur complex is obtained from longer wavelengths. The MCD is smaller than the natural CD for the magnetic field strength used in these experiments and only slightly greater than the limit for detectability according to the criterion of Sutherland (1978). There are clear differences between these spectra and those of other iron-sulfur proteins.…”

Section: Resultsmentioning

confidence: 87%

“…MCD spectra were measured at a magnetic field strength of 1.1 T. Both the spectrophotometer and the polarization and emission spectrometer were operated under the control of a computer (Tektronix, Beaverton, OR, Model 4051). The interfaces between the computer, the spectrophotometer, and the P/E spectrometer have been described elsewhere (Sutherland & Boles, 1978;Sutherland et al, 1980). Spectra were stored on flexible disks for post-experimental analysis.…”

Section: Methodsmentioning

confidence: 99%

Analysis of the iron-sulfur cluster of aconitase by natural and magnetic circular dichroism

1981

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We have examined the iron-sulfur cluster of aconitase, a high-potential iron-sulfur protein, by absorption, circular dichroism (CD), and magnetic circular dichroism (MCD) spectroscopy. The MCD spectrum of unactivated aconitase, which is presumably oxidized, is similar to those of reduced two iron-two sulfide ferredoxins but distinct from the MCD of known four iron-four sulfide proteins. The magnitude of the natural CD of unactivated aconitase also suggests the absence of four iron-four sulfur clusters. Reduction of the enzyme with dithionite and activation with the cysteine-ascorbate-ferrous ion activation mixture generate spectra which are significantly different from those of any iron-sulfur protein seen to date. We interpret these results as indicating that aconitase does not contain a four iron-four sulfur cluster generally thought to be characteristic of high-potential iron-sulfur proteins. It could contain a two iron-two sulfur center or some other center such as a cyclic three iron-three sulfur center.

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Universal computer interface for the Cary 118C spectrophotometer

Cited by 17 publications

References 7 publications

Absorption Spectrum of DNA for Wavelengths Greater than 300 nm

Absorption Spectrum of DNA for Wavelengths Greater than 300 nm

Z-DNA: vacuum ultraviolet circular dichroism.

Analysis of the iron-sulfur cluster of aconitase by natural and magnetic circular dichroism

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