Search PubMed⌕ Search

Biomedical subjects

W A Cramer

Publications and source records attributed to W A Cramer.

At least 127 records · Page 7Linked to original sources
PubMed1976

Changes in rotational motion of a cell-bound fluorophore caused by colicin E1: a study by fluorescence polarization and differential polarized phase fluorometry.

The stationary fluorescence polarization and the differential phase delay of the polarized components of the fluorescence of 1-phenylnaphthylamine in Escherichia coli suspensions were measured before and after addition of colicin E1. Both sets of measurements register an increase in the rotational relaxation time of the fluorescent probe when colicin is present. These increases are absent in an E. coli mutant tolerant to colicin E1. The physical interpretation of the changes demands separate estimation of the fraction f2 of the emitting fluorophores that change their properties upon colicin addition and of the rotational relaxation time p2 of this fraction, following the colicin-induced changes. By themselves, the steady state polarizaiton observations permit only the conclusion that f2 must be in the range of 1-0.06 and the change in p2/pi between 1.5 and a value larger than 10. Combination of the data of stationary polarization with those of differential phase fluorometry results in an important reduction in the uncertainty:f2 must be in the range 1-0.33 and the change in p2/pi in the range 1.5-2.5.

Binding Sites↗
PubMed1976

Stimulation of photosystem I-induced oxidation of chloroplast cytochrome b-559 by pre-illumination and by low pH.

(1) The proportion of higher plant chloroplast cytochrome b-559 oxidizable during illumination by low intensity 732 nm light increases as the pH is decreased below 6.5. At pH 5.0-5.3 total oxidation is seen and subsequent red light can cause reduction of up to 2/3 of the oxidized cytochrome. The oxidation by far red light at pH 5 is inhibited by 2 muM 2,5-dibromo-3-methyl-6-isopropyl-rho-benzoquinone whereas the red light-induced reduction is inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. In this pH range ferricyanide-oxidized cytochrome b-559 exists in a form not reducible by ferrocyanide. (2) An increase in the amplitude of far-red induced oxidation also occurs at higher pH (up to pH 7.8) after pre-treatment of chloroplasts with substantially higher levels of light (approx. 10(6) ergs-cm-2-s-1). The degree of light activation is pH dependent, being more pronounced at lower pH. After light activation, cytochrome b-559 can be completely oxidized by far-red light in a manner reversible by red light up to pH values of 6, and the curve describing the amplitude of far-red oxidation as a function of pH is shifted by 0.5-1.0 pH unit toward higher pH. Far-red oxidation and red light reduction are again inhibited by 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone and 3-(3,4-dichlorophenyl)-1,1-dimethylurea, respectively. (3) Light activation at pH 5.2-6.0 is also manifested in a small decrease in the amplitude of subsequent dark ferrocyanide reduction, and this decrease is inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (10 muM). (4) The effect of intramembranal acidity on the effective redox potential of cytochrome b-559 and its function is discussed.

Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone↗
PubMed1976

Changes in E. coli cell envelope structure caused by uncouplers of active transport and colicin E1.

It is of interest to inquire whether agents that uncouple or deenergize membranes cause concomitant structural changes. The agents considered here are the uncoupler carbonyl cyanide-p-trifluoromethoxyphenylhydrazone and the bacteriocidal protein colicin E1, agents for which there is some precedent for believing that they interact with membranes. In intact E. coli ML 308-225 cells the inhibition of [14C]-PROLINE ACtive transport by FCCP increases with uncoupler concentration from approximately 20% at 2 muM to approximately 100% at 5 muM. The increase in the rotational relaxation time (rho) of the cell-bound fluorescent probe N-phenyl-1-naphthylamine (PhNap)1 and 8-anilino-1-naphthalene-sulfonate (ANS) under these conditions shows the same dependence on FCCP concentration. For cells treated with EDTA to remove part of the outer lipopolysaccharide layer, inhibition of proline transport and the increase in rho value of ANS show the same dependence on FCCP concentration with saturation at 0.3 muM. EDTA treatment causes a large increase in the binding and rotational relaxation time of PhNap, the latter quantity approaching a value obtained with purified inner membrane. Similar effects are produced in untreated cells by 5muM FCCP...

Biological Transport, Active↗
PubMed1976

Evidence for an increase in microviscosity of plasma membranes from soybean hypocotyls induced by the plant hormone, indole-3-acetic Acid.

The plant hormone indole-3-acetic acid (IAA or auxin) added at a concentration for half-maximal promotion of cell elongation (1 mum) caused an increase of 25% in the fluorescence polarization of the membrane-bound probe N-phenyl-1-naphthylamine, when added to fractions enriched in plasma membranes from soybean hypocotyls (Glycine max L. var. Wayne), with no measurable change in fluorescence lifetime. The amplitude of the polarization increase was maximal in the temperature range 12 to 22 C. The findings provide evidence for a cell-free response of isolated plasma membranes to the hormone and imply that the response involves an increase in the microviscosity of hydrocarbon regions of the membrane.

Journal Article↗
PubMed1975

Light-induced turnover of chloroplast cytochrome b-559 in the presence of N-methylphenazonium methosulphate.

In the presence of 0.1-5 muM N-methylphenazonium methosulphate approx. 50-70% oxidation of cytochrome b-559 can be induced by far-red light. The oxidation is best observed with long wavelength far-red light (732 nm) of moderate intensities (approx. 10(4) ergs/cm2 per s) and is reversed by subsequent illumination with red light. Concentrations of N-methylphenazonium methosulphate above 5 muM are inhibitory probably due to cyclic electron flow. The far-red oxidation is inhibited by low concentrations of the plastoquinone antagonist 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, while 3-(3,4-dichlorophenyl)-1,1-dimethylurea inhibits red light reduction and increases the amplitude of far-red oxidation. The effect of N-methylphenazonium methosulphate is mimicked by N-methyl-phenazonium ethosulphate, but not by pyocyanine or diaminodurene. Low concentrations (2-3 muM) of N-methylphenazonium methosulphate also stimulate a 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone-inhibitable red light reduction of cytochrome f.

Chlorophyll↗