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Biomedical subjects

B S Hudson

Publications and source records attributed to B S Hudson.

22 records · Page 2Linked to original sources
PubMed1977

Conjugated polyene fatty acids as fluorescent probes: biosynthetic incorporation of parinaric acid by Escherichia coli and studies of phase transitions.

The use of the fluorescent fatty acid, parinaric acid (9, 11, 13, 15-octadecatetraenoic acid) (PnA), was studied in cells of an unsaturated fatty acid auxotroph of Escherichia coli. Growth conditions were found that permitted biosynthetic incorporation of PnA (up to 3%) into membrane phospholipids during growth on oleic or elaidic acid. Fluorescence measurements of incorporated PnA revealed phase transitions in cells, membranes, and phospholipids at temperatures that reflected the fatty acid composition of the sample. Transitions had a well-defined onset from high temperature, while the lower and end point was less well defined. cis- and trans-PnA (cis, trnas, trans, cis, and all trans, respectively) gave comparable results. Similar phase transitions were detected with PnA, which was not biosynthetically incorporated. Fluorescence of tryptophan was measured in E. coli membranes as a function of concentration of PnA. Significant quenching of tryptophan fluorescence by PnA was observed.

Cell Membrane↗
PubMed1976

Conjugated polyene fatty acids as fluorescent membrane probes: model system studies.

The use of conjugated polyene fatty acids as probes of membrane structure is examined, alpha- and beta-parinaric acid (cis, trans, trans, cis- and all trans-9, 11, 13, 15-octadecatetraenoic acid) and synthetic lecithins containing an alpha-parinaric acid chai in position 2 have been prepared, and their absorption and fluorescence properties have been determined. Their absorption spectra are at sufficiently long wavelength to be unobscured by cellular chromophores such as nucleotides and aromatic amin acids. Parinaric acid absorption does, however, overlap tryptophan emission which allows fluorescence energy transfer. Potential uses of these fluorescent probes are presented with studies on mode systems with known physical properties. Dipalmitoyl phosphatidylcholine exhibits a sharp phase transition 1 degree wide at 42 degrees C, as monitored by the fluorescence intensit of parinaric acid. The magnitude of the transition is independent of probe concentration, but the width of the transition and hysteresis are dependent upon such factors as the probe concentration and whether or not sonication is used in sample preparation. Using both fluorescence and absorption properties of the probe, we show that the addition of cholesterol to the dispersion broadens and decreases the magnitude of the transition. These results are interpreted in terms of a change in the polarizability of the acyl chains of a lipid bilayer undergoes a thermal transition. Lipid-protein interactions are studied by the binding of alpha-parinaric acid to bovine serum albumin. Fluorescence enhancement, absorption spectral shifts, and quenching of tryptophan fluorescnece are observed when alpha-parinaric acid binds to bovine serum albumin. Calculations based on these measurements are consistent with two binding sites of KB approximately 10(8) (M-1) and three to four binding sites of KB approximately 10(6)-10(7) (M-1), similar to known values for the binding of other long-chain fatty acids. Biosynthetic incorporation of beta-parinaric acid into the E. coli fatty acid auxotroph 30E betaox has been accomplished and phase transitions in cells and isolated phospholipids are shown.

Cell Membrane↗
PubMed1975

Conjugated polyene fatty acids as membrane probes: preliminary characterization.

The use of fluorescent conjugated polyenoic fatty acids as probes of membrane structure is introduced. alpha- and beta-parinaric acid (cis, trans, trans, cis-, and all trans-9,11,13,15-octadecatetraenoic acid) and synthetic lecithins containing an alpha-parinaric acid chain in position 2 are prepared and their absorption and fluorescence properties are determined. Phase transitions are detected as fluorescence changes at characteristic temperatures when either the free fatty acid probes or the labeled phospholipid probe are included in sonicated aqueous dispersions of L-alpha-dimyristoyl lecithin, L-alpha dipalmitoyl lecithin, or L-alpha-distearoyl lecithin. The phase transitions are detected at about 23 degrees C (dimyristoyl), 44 degrees C (dipalmitoyl), and 53 degrees C (distearoyl lecithin). Binding of alpha-parinaric acid to bovine serum albumin is measured by shifts in the absorption spectrum and enhanced quantum yield of the fatty acid upon binding and by energy transfer between 2 tryptophyl residues in bovine serum albumin and alpha-parinaric acid. Approximately six binding sites are detected. Other applications of these probe molecules, including phase transitions of phospholipid/cholesterol dispersions, induced circular dichroism of parinaric acid bound to albumin, and biosynthetic incorporation of parinaric acid into biological membranes, are discussed.

Fatty Acids, Unsaturated↗