Kinetics of transfer of pyrene and rac-1-oleyl-2-[4-(3-pyrenyl)butanoyl]glycerol between human plasma lipoproteins.
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Diglycerides↗
Biomedical subjects
S C Charlton
Publications and source records attributed to S C Charlton.
Solid-phase colorimetric determination of potassium.
A nonpolar organic film (plasticized polyvinyl chloride) containing the ionophore valinomycin was incubated with an aqueous solution containing potassium ion and a detectable anion (erythrosin B). The amount of erythrosin B retained by the film after washing could be measured by absorbance or reflectance, and was directly related to the potassium concentration. This dye-binding method is quantitative for potassium and is suitable for both aqueous and serum-based solutions. There was no interference by sodium in the range found in serum. Several polyvinyl chloride plasticizers and anionic dyes and some other ionophores were found to be useful. The anion binding is thought to be restricted to the surface.
Colorimetry↗
Cholesteryl ester-rich microemulsions: stable protein-free analogs of low density lipoproteins.
A method has been devised for the preparation of stable lipid microemulsions containing cholesterol, cholesteryl ester, phosphatidylcholine, and trioleoylglycerol in the relative molar ratios found in low density lipoproteins. Gel permeation chromatography showed these microemulsions to be essentially homogeneous with respect to chemical composition. Omission of triolein or substitution of a diunsaturated phosphatidylcholine for either a disaturated or monosaturated-monounsaturated phosphatidylcholine destroyed the observed homogeneity of the microemulsions. The particle diameter of the negatively-strained relative elution volumes of the cholesteryl ester-rich microemulsion, VLDL2, VLDL3, and LDL indicated a mean diameter of about 35 nm. The cholesteryl ester-rich microemulsion can be used as a cholesteryl ester donor for plasma protein-mediated transfer of cholesteryl ester to plasma lipoproteins and for studying apoprotein-lipid interactions.
Apolipoproteins↗
A fluorescence stopped flow analysis of Ca2+ exchange with troponin C.
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Binding Sites↗
Properties of cupric ions in benzylamine oxidase from pig plasma as studied by magnetic-resonance and kinetic methods.
Benzylamine oxidase from pig plasma has been studied by a variety of chemical and physical techniques. 1. Analytical ultracentrifugation, gel electrophoresis and isoelectric-focusing studies suggest that the enzyme is composed of two subunits with closely similar primary structures. 2. E.s.r. and n.m.r. measurements show that the enzyme contains two well-separated (greater than 0.6 nm) Cu2+ ions at chemically distinct sites. Each Cu2+ ion is coordinated by two water molecules, one 'axial' and the other 'equatorial'. Both water molecules undergo fast exchange (10(5)--10(8) s-1) with solvent and are deprotonated in the pH range 8--9, but only the equatorial water molecule is displaced by the inhibitors N3- and CN-. 3. Kinetic and e.s.r. measurements show that azide and cyanide compete against O2 binding and also make the two Cu2+ sites identical. It is concluded that Cu2+ must participate in the re-oxidation of reduced enzyme by molecular O2.
Animals↗
Kinetics of rac-1-oleyl-2-[4-(3-pyrenyl)butanoyl]glycerol transfer between high density lipoproteins.
The mechanism of transfer of diglyceride between high density lipoproteins (HDL) was investigated with a pyrene-containing analogue whose fluorescent properties depend on the microscopic concentration in the lipoprotein. Transfer rates were first order, rapid (3.5s-1), and invariant over a 100-fold range of HDL concentration and over a 10-fold range of rac-1-oleyl-2-[4-(3-pyrenyl)butanoyl]glycerol concentrations. Similar behavior of the probe was observed with HDL3, although the rate was 40% slower. These results support a mechanism in which rate-limiting dissociation of the diglyceride analogue from one HDL particle into the aqueous phase precedes rapid diffusion and subsequent uptake by another such particle.
Diglycerides↗
Stopped flow kinetics of pyrene transfer between human high density lipoproteins.
The transfer of pyrene between high density lipoproteins was studied as a model of lipid exchange. When high density lipoprotein containing pyrene was mixed with unlabeled lipoprotein, pyrene excimer fluorescence decreased with a half-time of approximately 3 ms. The rate of pyrene transfer was invariant over a 100-fold range of unlabeled lipoprotein concentrations. Since a decrease in excimer fluorescence indicates a decrease in the microscopic concentrations of pyrene, the observed fluorescence change relfects pyrene transfer to unlabeled lipoproteins, and, therefore, dilution of the pyrene molecules. When high density lipoprotein labeled with pyrene was rapidly diluted 1:14 into buffer, a small decrease in excimer fluorescence was observed. The half-time of this fluorescence change was also about 3 ms and represents the half-time for the dissociation of pyrene from high density lipoprotein into water. The latter observation, coupled with the invariant exchange rate with lipoprotein concentration suggests strongly that the limiting step in the transfer of pyrene between high density lipoproteins is the dissociation of pyrene into solvent. Finally, regardless of mechanism, the exchange of pyrene, and presumably other hydrophobic aromatic compounds, among serum high density lipoproteins is extremely fast. This result indicates that these types of compounds can be rapidly assimilated and transported through the body by plasma lipoproteins.
Binding Sites↗