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Mass Spectrometric Analysis
Published in Adorjan Aszalos, Modern Analysis of Antibiotics, 2020
Alamethicin I (Figure 2) has also been characterized by californium-252 PD [247]. The positive ion spectrum is more helpful, providing (M + Na)+ and (M + 2Na − H)+ adduct ions and fragment ions, which coincides with the peptide sequence; N-imine ions corresponding to cleavages of 16 of the 19 peptide bonds are observed. The negative ion spectrum exhibits a (M − H)− ion but few useful fragment ions.
Clinical Considerations in Radiotracer Biodistribution Studies
Published in Lelio G. Colombetti, Biological Transport of Radiotracers, 2020
Lipid bilayer membranes are highly impermeable to small inorganic ions. A variety of molecules, including the antibiotics valinomycin and nonactin, interact with lipid bilayer membranes and increase their permeability to small ions via a carrier mechanism comparable to the highly ion-permeable nerve membranes. Other membrane-modifying molecules, such as gramicidin A and alamethicin, facilitate the passive diffusion of ions by creating a pathway through the membrane through which ions can move down an electrochemical gradient. Other pore-forming antibiotics are nystatin and amphotericin B.10
Biomedical Applications of Raman Scattering
Published in R. Michael Gendreau, Spectroscopy in the Biomedical Sciences, 1986
A variety of Raman spectroscopic studies have appeared along these general lines. The interaction of lysozyme (not an integral membrane protein) with liposomes formed from a mixture of the phospholipids 1,2-dipalmitoyl-L-phosphatidic acid/1,2 dimyristoyl-L-phosphatidylcholine was studied by Lippert et al.81 At temperatures < 27°C, interaction of protein with lipid slightly increased the amount of helical structure in lysozyme, while above 30°C, considerable β-sheet was formed. The onset of β-structure was accompanied by the introduction of disorder into the lipid side chains. The results were interpreted in terms of both polar interactions between the acidic lipid component at temperatures where the lipids are in the gel state and hydrophobic interactions between lipid and protein at higher temperatures. Lis et al.82 examined the effect of the ionophores alamethicin and valinomycin on phospholipid organization. Both peptides tended to fluidize dimyristoyl lecithin but produced little alteration in the chain conformation of dipalmitoyl lecithin (DPPC). Detailed temperature studies were not reported. In contrast, Verma and Wallach83 suggested that the peptide mellitin tends to rigidify DPPC multibilayers. In a more thorough investigation of the same system,84 Levin and co-workers demonstrated two melting events when the peptide was inserted into dimyristoylphosphatidylcholine (DMPC). The primary gel/liquid-crystal transition is depressed when the peptide concentration is increased. The concentration-independent higher-temperature transition is associated with the melting of lipids present at the lipid-polypeptide interface. It was estimated that about six lipid molecules fall into this category.
Characterisation of UDP-glucuronosyltransferase activity in sea turtle Chelonia mydas
Published in Xenobiotica, 2022
Vera Helena V. Dias, Jacó J. Mattos, Camila L. V. Bastolla, Karim H. Lüchmann, Afonso C. D. Bainy
Lithocholic acid, taurocholic acid, diclofenac, ibuprofen, and paracetamol were screened as inhibitors of UGT enzymes. Activity assays were performed in liver microsomes (as described earlier) in the presence of chemical inhibitors (100 µM final concentration). Besides substrates and inhibitors, we only used alamethicin (22 µg/mg of protein) as a membrane-disrupting agent. Methanol concentration was below 0.5%.4-MU final concentration (100 µM) was lower than in other assays, since high substrate concentration reduces this inhibition. Nevertheless, the concentration of 100 µM of 4-MU used in the inhibitors experiment may underestimate the potential effects of some weak inhibitors, mainly the competitive type. Thus, the results should be interpreted with caution, as some potential inhibitors tested here may show an inhibitory effect on enzyme activity at lower 4-MU concentrations, which were not examined in this study.
A cysteine trapping assay for risk assessment of reactive acyl CoA metabolites
Published in Xenobiotica, 2022
Nobuyuki Kakutani, Satoru Kobayashi, Toshio Taniguchi, Yukihiro Nomura
To increase the sensitivity of the assay, the supplements for the acyl CoA metabolic assay were investigated. The addition of DTT dramatically increased the sensitivity of the assay for acyl CoA metabolites and Cys conjugates. It is considered that DTT helped the thiol moieties of Cys and CoA maintain their reduced forms, which are required for the nucleophilic reaction. Triton X-100 was added, and its effect was compared with that of the pore-forming peptide alamethicin. Triton X-100 increased the metabolic activity of acyl CoA, whereas alamethicin had no such effect (Figure 4). The DMSO concentration did not affect the assay results up to at least 1% in these conditions (Supplement Figure 1). When lysine was used instead of cysteine, the corresponding conjugates were detected in only trace amounts (Supplement Figure 2).
In vitro modulatory effects of ginsenoside compound K, 20(S)-protopanaxadiol and 20(S)-protopanaxatriol on uridine 5′-diphospho-glucuronosyltransferase activity and expression
Published in Xenobiotica, 2021
Su-Nyeong Jang, So-Young Park, Hyunyoung Lee, Hyojin Jeong, Ji-Hyeon Jeon, Im-Sook Song, Mi Jeong Kwon, Kwang-Hyeon Liu
Androsterone, berberine, chenodeoxycholic acid (CDCA), cotinine, carvedilol, estrone-β-D-glucuronide (EG), schisandrin A, N-acetylserotonin, naloxone, testosterone, trifluoperazine, and uridine 5′-diphospho-glucuronic acid (UDPGA) were purchased from Sigma-Aldrich (St. Louis, MO). 7-ethyl-10-hydroxy camptothecin (SN-38) was provided by Santa Cruz Biotechnology (Dallas, TX). Alamethicin (from Trichoderma viride), CDCA 24-acyl-β-D-glucuronide, and mycophenolic acid were obtained from Toronto Research Chemicals (Toronto, ON, Canada). CK (98.0%), PPD (98.0%), and PPT (98.0%) were purchased from the Ambo Institute (Daejeon, Korea). All solvents were liquid chromatography-tandem mass spectrometry (LC-MS/MS) grade (Fisher Scientific, Pittsburgh, PA). Pooled human liver microsomes (HLMs, H2630, and mixed gender) were obtained from XenoTech (Lenexa, KS, USA)), and rUGTs (UGT1A1, 1A3, 1A4, 1A6, 1A9, 2B4, 2B7, 2B10, 2B15, and 2B17) and cryopreserved human hepatocytes (HFC520) were purchased from Corning Life Sciences (Woburn, MA, USA).