PubMed Health⌕ Search

Biomedical subjects

E Kay

Publications and source records attributed to E Kay.

At least 109 records · Page 6Linked to original sources
PubMed1976

Double-stranded DNA in methanol-ethanol-buffer solvent system.

DNA in a solvent system consisting of roughly equal volumes of methanol and ethanol and 5% buffer has a conservative circular dichroism (CD) spectrum of very low intensity above 220 nm and an increase of epsilon258 comparable to that of denatured DNA (about 40%). A direct comparison of this spectrum with the CD of single-stranded DNA reveals many differences, indicating DNA in this solvent system has a conformation different from that of denatured DNA. When the alcohols are removed, the B form conformation and normal epsilon258 are restored in native DNA, while single-stranded DNA remains denatured. A double-stranded structure of DNA in the methanol-ethanol-buffer solvent system is confirmed by the neutral cesium chloride density gradient centrifugation of DNA in which one chain is labeled with [14C]thymidine and the other [3H]5-bromodeoxyuridine. The doubly labeled DNA exposed to the alcohol solvent system has a centrifugal pattern identical with that of control DNA; the two radioactivities cosediment and form a superimposing band, distinctly different from that of single-stranded DNA; 3H-labeled (thymidine) chains sediment further than 14C-labeled chains (5-bromo-deoxyuridine). Denatured DNA exhibits varying CD spectra depending on solvents. It is suggested that single-stranded DNA in different solvent systems assumes different modes of base stacking.

Animals↗
PubMed1976

Origins of circular dichroism bands in Bowman-Birk soybean trypsin inhibitor.

The spectral properties of Bowman-Birk soybean trypsin inhibitor (BBI) were investigated by analyzing difference absorption spectra and difference CD spectra and by comparing them with those of tyrosyl model compounds. The O-acetylation of tyrosyl side chains showed that the ultraviolet CD bands of BBI above 225 nm originate from disulfide side chains and tyrosyl phenolic groups; phenylalanyl residues do not give rise to detectable CD in BBI in this wavelength region. The results of the tyrosyl ionization experiment were consistent with this interpretation. A broad negative CD band centered around 280 nm in BBI arises mainly from disulfide bonds (epsilonL - epsilonR = -0.83 M-1 cm-1 per disulfide). Each of 2 tyrosyl residues gives rise to negative CD in this region; together they contribute approximately 10% of the total CD intensity at 277 nm (epsilonL - epsilonR = -0.36 M-1 cm-1 per tyrosyl). Disulfide bonds in BBI also have a broad positive CD band centered around 240 nm (epsilonL- epsilonR = 0.9 M-1 per disulfide(. Tyrosyl side chains give rise to a sharp positive peak at 231 nm, overlapping with the positive disulfide CD. Dimerization of monomeric BBI did not alter the CD profile. One of two tyrosyl phenolic groups is relatively exposed and can be 0-acetylated by 100- to 1500-fold molar excess of N-acetylmidazole. The other is inaccessible to the reagent even in the presence of 8 M urea, but can be acetylated in the presence of 6 M guanidine hydrochloride. Fully acetylated BBI has the near-ultraviolet disulfide CD and the far-ultraviolet polypetide CD very similar to those of the native inhibitor, indicating the O-acetylation of two tryosyl side chains did not induce much conformational change in BBI. The near-ultraviolet CD of BBI was altered in the presence of 8 M urea of 6 M guanidine hydrochloride, with a greater change brought about by the latter. Dithiothreitol (20 mM) completely abolished the tyrosyl and disulfide CD in this region.

Binding Sites↗