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Role of Tumor Cell Membrane in Hyperthermia
Published in Leopold J. Anghileri, Jacques Robert, Hyperthermia In Cancer Treatment, 2019
There is considerable evidence that is contrary to the fluid mosaic model: all lipids in biological membranes are not in the same fluid state at physiological temperatures. Spin-label experiments have shown the existence of discrete lipid domains.8–11 An asymmetric arrangement of phospholipids about the outer and inner lipid layers of the plasma membrane, with negatively charged (acidic) lipids (phosphatidylserine, phosphatidylinositol, etc.), predominantly in the cytosol half of the bilayer, has been demonstrated.12 Distinct clusters of phospholipids have been detected in erythrocyte membrane.13 Cholesterol also appears not randomly distributed in plasma membranes.14 This phenomenon of cholesterol-poor and cholesterol-rich domains is consistent with the presence of domains of specific phospholipids having high affinity for the sterol.15
Ferrihemoglobin in Normal Blood
Published in Manfred Kiese, Methemoglobinemia: A Comprehensive Treatise, 2019
Davenport et al.394 found a heat-labile non-dialyzing factor in chloroplasts which is reduced by illuminated chloroplasts and transfers electrons to ferrimyoglobin. Hayashi and Stamatoyannopoulos395 showed that this factor is ferredoxin and, with the ferredoxin-NADP reductase system, used it for the reduction of ferrihemoglobin. Reduced ferredoxin seems to react specifically with the iron in ferrihemoglobin. Asakura et al.396 used it for the reduction of spin-labeled ferrihemoglobin, in which a spin label was attached to one of the propionic acid groups of the porphyrin.
Instrumentation
Published in Clive R. Bagshaw, Biomolecular Kinetics, 2017
Electron paramagnetic (spin) resonance (EPR/ESR) signals arise from unpaired electrons and are therefore of limited occurrence in stable molecules. However, where such species exist, a wealth of specific structural and kinetic information can be obtained [527]. In addition, stable free radicals (spin labels) may be used as probes in a similar way to labeling with extrinsic fluorophores. The methodology is particularly important in the study of photosynthesis and redox reactions where free radicals are transient species. The EPR phenomenon involves the absorption of microwave radiation (typical frequency 8 to 35 GHz) by the sample when placed in a magnetic field. This property limits the sample size of aqueous samples because water absorbs strongly in the microwave region. Note also that the energy associated with a photon of microwave radiation is ≪kbT at ambient temperatures (Table 7.4), and therefore, the populations of spin states that undergo the transition are similar, with only a small excess in the low energy state. Compare this with visible absorption spectroscopy where the ground state has practically 100% occupancy in the dark. In practice, due to the detection method, EPR is reasonably sensitive and can report on species in the sub-micromolar range. However, in the case of signals from macromolecules, which tumble slowly, spectral anisotropies are not averaged out, leading to broader and weaker signals.
Interaction of Alpha-Crystallin with Phospholipid Membranes
Published in Current Eye Research, 2021
Laxman Mainali, William J. O’Brien, Raju Timsina
The CSL spin labels are located in both regions in the membrane, i.e., in the region where α-crystallin is bound to the membrane and in the region where α-crystallin is not bound in the membrane. Therefore, we expect to have two values of the T1−1’s from these two regions; however, we get only one average T1−1 value (see Figure 8a). This indicates that the exchange rate of CSL spin labels in membranes between the bound α-crystallin and unbound α-crystallin is greater than T1−1 giving an averaged T1−1. This exchange rate between these bound and unbound α-crystallin regions in the membrane is faster when compared with the spin–lattice relaxation rate of lipid spin labels in membranes between 105 and 106 s−1 (T1 from 1 to 10 µs). This faster exchange rate implies that the bound α-crystallin membrane regions should be small, allowing us to hypothesize that it is likely that the α-crystallin monomer or smaller oligomers with few subunits are participating in binding rather than the larger oligomers of α-crystallin.
Liposomal integration method for assessing antioxidative activity of water insoluble compounds towards biologically relevant free radicals: example of avarol
Published in Journal of Liposome Research, 2020
Đura Nakarada, Boris Pejin, Giuseppina Tommonaro, Miloš Mojović
In order to assess the lipid bilayer dynamics of liposomes and their ability to resist the oxidative degradation towards hydroxyl (•OH), superoxide anion (O2•−) and NO• radicals, spin-labelled fatty acid 5-DS (Figure 2) was used on avarol-containing and 100% DPPC liposomes. Integration of this spin-label into liposomal assembly structures provides information on local fluid dynamics (Codd and Seymour 2008). 5-DS is labelled with a nitroxide doxyl group (stable radical) at 5 – position located at the beginning of the doxyl surfactant hydrophobic tail. 5-DS becomes incorporated into the liposomal bilayer, without forming a separate phase (Fukuda et al.2001, Codd and Seymour 2008). Motion and angular orientation of the nitroxide group with the respect to the membrane lipid-water interface directly affects the EPR spectral shape of spin-labelled stearic acid (Da Silveira et al.2003). Depending on the position of the doxyl group along the hydrocarbon chain, motional freedom in the membrane can be probed at different depths of the bilayer. 5-DS is used to probe the area close to the surface of the lipid bilayer (Pavićević et al.2014).
Impaired albumin function: a novel potential indicator for liver function damage?
Published in Annals of Medicine, 2019
Lejia Sun, Huanhuan Yin, Meixi Liu, Gang Xu, Xiaoxiang Zhou, Penglei Ge, Huayu Yang, Yilei Mao
The long-chain fatty acid-binding ability of albumin can be quantified using electron paramagnetic resonance (EPR) techniques (Jalan et al. 2009; Haeri et al. 2019). There are seven fatty acid-binding sites on an albumin molecule, of which three have high affinity and the other four have lower affinity. First, 16-Hexyl stearic acid is used as a spin label and is added to plasma samples at a specific concentration, then ethanol is added as a polar reagent and the mixture is incubated for 10 min. When the albumin structure is broken down, the free spin label increases and can be detected and recorded using EPR spectroscopy. ‘H’ and ‘L’ are used to represent the affinity of the high and low affinity fatty acid binding sites, respectively, and the ratio H/L reflects conformational changes in the albumin molecule (Ge, Liao, et al. 2016).