Amino acid receptor channels in taste cells.
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Animals↗
Biomedical subjects
G Smutzer
Publications and source records attributed to G Smutzer.
A simplified method for drying agarose gels.
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Electrophoresis, Agar Gel↗
A fluorescent sterol probe study of cholesterol/phospholipid membranes.
The behavior of dehydroergosterol in L-alpha-dimyristoylphosphatidylcholine (DMPC) unsonicated multilamellar liposomes was characterized by absorption spectroscopy and fluorescence measurements. Dehydroergosterol exhibited a lowered absorption coefficient in multilamellar liposomes while the steady-state fluorescence anisotropy of dehydroergosterol in these membranes decreased significantly with increasing dehydroergosterol concentration, suggesting membrane sterol-sterol interactions. The comparative steady-state anisotropy of 0.9 mole percent dehydroergosterol in multilamellar liposomes was lower than in small unilamellar vesicles suggesting different sterol environments for dehydroergosterol. Dehydroergosterol fluorescence lifetime was relatively independent of membrane sterol content and yielded similar values in sonicated and unsonicated model membranes. In multilamellar liposomes containing 5 mole percent cholesterol, the gel-to-liquid crystalline phase transition of DMPC detected by 0.9 mole percent dehydroergosterol was significantly broadened when compared to the phase transition detected by dehydroergosterol in the absence of membrane cholesterol (Smutzer, G. et al. (1986) Biochim. Biophys. Acta 862, 361-371). In multilamellar liposomes containing 10 mole percent cholesterol, the major fluorescence lifetime of dehydroergosterol did not detect the gel-to-liquid crystalline phase transition of DMPC. Time-correlated fluorescence anisotropy decays of dehydroergosterol in DMPC multilamellar liposomes in the absence and presence of 5 mole percent cholesterol exhibited a single rotational correlation time near one nanosecond that was relatively independent of temperature and low concentrations of membrane cholesterol. The limiting anisotropy of 0.9 mole percent dehydroergosterol decreased above the gel-to-liquid crystalline phase transition in membranes without cholesterol and was not significantly affected by the phase transition in membranes containing 5 mole percent cholesterol. These results suggested hindered rotational diffusion of dehydroergosterol in multilamellar liposomes. Lifetime and time-correlated fluorescence measurements of 0.9 mole percent dehydroergosterol in multilamellar liposomes further suggested this fluorophore was detecting physical properties of the bulk membrane phospholipids in membranes devoid of cholesterol and was detecting sterol-rich regions in membranes of low sterol concentration.
Cholesterol↗
A fluorescent sterol probe study of human serum low-density lipoproteins.
The fluorescent sterol probe, ergosta-5,7,9,(11),22-tetraen-3 beta-ol (dehydroergosterol), was utilized as a cholesterol analog to label human serum low-density lipoproteins (LDL). Quenching of dehydroergosterol fluorescence by KI indicated that most of the fluorophore was either buried within the outer phospholipid monolayer of LDL or within the neutral lipid core of LDL. The steady-state anisotropy of dehydroergosterol in LDL detected the cholesteric core phase transition near 30 degrees C. Fluorescence lifetime decays for dehydroergosterol contained two components, both below and above the cholesteric phase transition, with the major lifetime component near 1 ns. Neither lifetime component underwent a detectable change in duration at the core phase transition temperature. Time-correlated fluorescence anisotropy decays of dehydroergosterol indicated a single rotational correlation time near 1.7 ns, which was unaffected by the core phase transition. Time-correlated anisotropy decays also suggested hindered rotation of dehydroergosterol in LDL. These results indicate that unesterified cholesterol is primarily located in the outer phospholipid monolayer of LDL, with the majority of cholesterol not in direct contact with the aqueous phase.
Calorimetry↗
Physical properties of the fluorescent sterol probe dehydroergosterol.
Spectroscopic studies were performed on the fluorescent sterol probes ergosta-5,7,9(11),22-tetraen-3 beta-ol (dehydroergosterol) and cholesta-5,7,9(11)-trien-3 beta-ol (cholestatrienol). In most isotropic solvents, these molecules exhibited a single lifetime near 300 ps. Fluorescence lifetimes in 2-propanol were independent of emission wavelength and independent of excitation wavelength. Excited state behavior of these probes appears relatively simple. In isotropic solvents, dehydroergosterol fluorescence emission underwent at most a small Stokes shift as solvent polarity was modified. Time-resolved anisotropy decays indicated that dehydroergosterol decay was monoexponential, with rotational correlation times dependent on solvent viscosity. When incorporated into L-alpha-dimyristoylphosphatidylcholine liposomes at a concentration of 0.9 mol%, dehydroergosterol fluorescence lifetime decreased at the phase transition of this phospholipid indicating that the sterol probe was detecting physical changes of the bulk phospholipids. Furthermore, total fluorescence decays and anisotropy decays were sensitive to the environment of the sterol. Dehydroergosterol and cholestatrienol are thus useful probes for monitoring sterol behavior in biological systems.
Cholestenes↗
Interactions between photosystem II components in chloroplast membranes. A correlation between the existence of a low potential species of cytochrome b-559 and low chlorophyll fluorescence in inhibited and developing chloroplasts.
1. Chloroplasts inhibited by incubation with hydroxylamine in the light exhibit a low fluorescence yield upon illumination in the presence of dithionite sufficient to completely reduce the primary acceptor, Q. In the absence of magnesium ions, the fluorescence yield is the same as in control chloroplasts, suggesting that the reason for the low yield is a defect in the mechanism by which Mg2+ enhances the fluorescence. These chloroplasts were previouly shown to contain only low potential (Em7.8 = +80 mV) cytochrome b-559 (Horton, P. and Croze, E (1977) Biochim. Biophys. Acta 462, 86-101). 2. In Photosystem II particles, in heat-treated chloroplasts and in trypsin-digested chloroplasts, high potential cytochrome b-559 is absent and the variable fluorescence yield is again low. 3. Peas grown under intermittent light contain only one-fifth of the content of high potential cytochrome b-559 seen in fully greened plants, yet show high rates of water to methyl viologen electron transport. Aquisition of the high potential cytochrome b-559 accompanies synthesis of chlorophyll b, the onset of Mg-stimulated fluorescence and an increased variable yield of fluorescence. A similar correlation was seen during greening of dark-grown barley. 4. It is proposed that the high potential state of cytochrome b-559 is due to the same membrane properties which allow cation enhanced variable fluorescence, so that the presence of low potential cytochrome b-559 is accompanied by a decrease in variable fluorescence yield.
Cell Membrane↗