PubMed Health⌕ Search

Biomedical subjects

J G Lees

Publications and source records attributed to J G Lees.

6 recordsLinked to original sources
PubMed2005

VUV irradiation effects on proteins in high-flux synchrotron radiation circular dichroism spectroscopy.

Synchrotron radiation circular dichroism (SRCD) spectroscopy is emerging as an important new tool in structural molecular biology. Previously we had shown that in lower-flux SRCD instruments, such as UV1 at ISA and beamline 3.1 at the SRS, vacuum ultraviolet (VUV) radiation damage to proteins was not evident after exposure over a period of hours. No effects were detected in either the protein primary or the secondary structures. However, with the development of high-flux beamlines, such as CD12 at the SRS, this issue has been revisited because of changes observed in the SRCD spectra of consecutive scans of protein samples obtained on this high-flux beamline. Experiments have been designed to distinguish between two different possible mechanisms: (i) photoionization causing free radicals or secondary electrons producing degradation of the protein, and (ii) local heating of the sample resulting in protein denaturation. The latter appears to be the principal source of the signal deterioration.

Circular Dichroism↗
PubMed2004

CDtool-an integrated software package for circular dichroism spectroscopic data processing, analysis, and archiving.

CDtool is a software package written to facilitate circular dichroism (CD) spectroscopic studies on both conventional lab-based instruments and synchrotron beamlines. It takes format-independent input data from any type of CD instrument, enables a wide range of standard and advanced processing methods, and, in a single user-friendly graphics-based package, takes raw data through the entire processing procedure and, importantly, uses data-mining techniques to retain in the final output all the information associated with the processing. It permits the facile comparison of data obtained from different instruments without the need for reformatting and displays it in graphical formats suitable for publication. It also includes the ability to automatically archive the processed data. This latter feature may be especially useful in light of recent funding institution directives with regard to data sharing and archiving and requirements for "good practice" and "traceability" within the pharmaceutical industry. In addition, CDtool includes a means of interfacing with protein data bank coordinate files and calculating secondary structures from them using alternate definitions and algorithms. This feature, along with a function that permits the facile production of new reference databases, enables the creation of specialized databases for secondary structural analyses of specific types of proteins. Thus the CDtool software not only enables rapid data processing and analyses but also includes many enhanced features not available in other CD data processing/analysis packages.

Archives↗
PubMed2003

Analyses of circular dichroism spectra of membrane proteins.

Circular dichroism (CD) spectroscopy is a valuable technique for the determination of protein secondary structures. Many linear and nonlinear algorithms have been developed for the empirical analysis of CD data, using reference databases derived from proteins of known structures. To date, the reference databases used by the various algorithms have all been derived from the spectra of soluble proteins. When applied to the analysis of soluble protein spectra, these methods generally produce calculated secondary structures that correspond well with crystallographic structures. In this study, however, it was shown that when applied to membrane protein spectra, the resulting calculations produce considerably poorer results. One source of this discrepancy may be the altered spectral peak positions (wavelength shifts) of membrane proteins due to the different dielectric of the membrane environment relative to that of water. These results have important consequences for studies that seek to use the existing soluble protein reference databases for the analyses of membrane proteins.

Animals↗
PubMed1990

Lamb ductus venosus: evidence of a cytochrome P-450 mechanism in its contractile tension.

We have recently shown that a cytochrome P-450-based mechanism is important for the generation of contractile tension by the ductus arteriosus and have now examined whether the same mechanism operates in the ductus venosus. Carbon monoxide (CO/O2 ratio, 0.27) and cytochrome P-450 inhibitors [metyrapone; 4-phenylimidazole; 14-isocyano, 15-(methoxymethyleneoxy)-5Z,8Z,11Z- eicosatrienoic acid; alpha-naphthoflavone] were tested in vitro on the ductus venosus sphincter from mature fetal lambs. Each preparation was precontracted with indomethacin (2.8 x 10(-6) M). Carbon monoxide completely relaxed the ductus, and its action was reversed by illumination with monochromatic light. Peak photocontraction occurred at 450 nm. With the exception of alpha-naphthoflavone, all cytochrome P-450 inhibitors were also relaxant agents. Alpha-naphthoflavone (the sole type I inhibitor tested) produced instead a modest contraction that was often transient. Relaxation brought about by both carbon monoxide and drugs was fully reversed by the thromboxane A2 analog 9,11-epithio-11,12-methano-thromboxane A2 and by excess potassium (55 mM). Carbon monoxide was equally effective in the intact ductus and the ductus denuded of endothelium, whereas cytochrome P-450 inhibitors were marginally less effective in the latter preparation. These findings indicate that the ductus venosus sphincter, like the ductus arteriosus, relies on an intramural cytochrome P-450 mechanism to develop its contractile tone. The actual constrictor remains to be characterized in both vessels.

Animals↗
PubMed1988

Further evidence implicating a cytochrome P-450-mediated reaction in the contractile tension of the lamb ductus arteriosus.

The authors have recently provided evidence implicating the cytochrome P-450 system in the generation of contractile tension of the ductus arteriosus. To confirm this possibility, carbon monoxide (CO/O2 ratio, 0.27) and cytochrome P-450 inhibitors [4-phenylimidazole; 14-isocyano,15-(methoxymethyleneoxy)-5Z,8Z,11 Z-eicosatrienoic acid; 9-hydroxyellipticine; alpha-naphthoflavone] were tested on the isolated ductus arteriosus from mature fetal lambs equilibrated at low (4-26 mm Hg) or high (229-694 mm Hg) O2 partial pressure (PO2). Carbon monoxide completely relaxed intact vessel wall preparations and preparations consisting of only the muscle. Carbon monoxide relaxation was reversed by illumination with monochromatic light and the peak for the photoactivated contraction occurred at 450 nm. 4-Phenylimidazole (100 and 1,000 microM) was also a relaxant agent, and its action was manifest at both low and high PO2. Unlike 4-phenylimidazole, the isonitrile compound (5 microM) and 9-hydroxyellipticine (10 and 100 microM) were relaxant only at low PO2 and were also less potent. At the same PO2, alpha-naphthoflavone (10 microM) barely reduced ductal tension. Treatment of the ductus with either a combination of superoxide dismutase (60 or 150 U/ml) and catalase (40 or 1,000 U/ml) or mannitol alone (80 mM) failed to alter the steady-state tone at low PO2 and the contractile response to O2. Arachidonic acid was tested on tissues pretreated with the dual cyclooxygenase and lipoxygenase inhibitor, BW755C (10 microM), and produced a weak relaxation at a concentration of 1 microM or higher. 5,6-Epoxytrienoic acid relaxed the untreated tissue, and its action was abolished by indomethacin (2.8 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗