PubMed · 15326682
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
National Toxicology Program. 2002. 2-Naphthylamine.. https://pubmed.ncbi.nlm.nih.gov/15326682/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Design of a partially cysteine-depleted C98S/C239S/C377S/C468A cytochrome P450 3A4 mutant designated CYP3A4(C58,C64) allowed site-directed incorporation of thiol-reactive fluorescent probes into alpha-helix A. The site of modification was identified as Cys-64 with the help of CYP3A4(C58) and CYP3A4(C64), each bearing only one accessible cysteine. Changes in the fluorescence of CYP3A4(C58,C64) labeled with 6-(bromoacetyl)-2-(dimethylamino)naphthalene (BADAN), 7-(diethylamino)-3-(4'-maleimidylphenyl)-4-methylcoumarin (CPM), or monobromobimane (mBBr) were used to study the interactions with bromocriptine (BCT), 1-pyrenebutanol (1-PB), testosterone (TST), and alpha-naphthoflavone (ANF). Of these substrates only ANF has a specific effect, causing a considerable decrease in fluorescence intensity of BADAN and CPM and increasing the fluorescence of mBBr. This ANF-binding event in the case of the BADAN-modified enzyme is characterized by an S50 of 18.2 +/- 0.7, compared with the value of 2.2 +/- 0.3 for the ANF-induced spin transition, thus revealing an additional low-affinity binding site. Studies of the effect of TST, 1-PB, and BCT on the interactions of ANF monitored by changes in fluorescence of CYP3A4(C58,C64)-BADAN or by the ANF-induced spin transition revealed no competition by these substrates. Investigation of the kinetics of fluorescence increase upon H2O2-dependent heme depletion suggests that labeled CYP3A4(C58,C64) is represented by two conformers, one of which has the fluorescence of the BADAN and CPM labels completely quenched, presumably by photoinduced electron transfer from the neighboring Trp-72 and/or Tyr-68 residues. The binding of ANF to the newly discovered binding site appears to affect the interactions of the label with the above residue(s), thus modulating the fraction of the fluorescent conformer.
The survival of Bradyrhizobium japonicum under hyperosmotic treatments achieved at various temperatures was investigated. The bacterial viability was measured at a combination of different levels of osmotic pressure (1.4-49.2 MPa) in glycerol solutions and temperature (4-28 degrees C). Viability was dependent on these two variables, with low temperatures (10 and 4 degrees C) exhibiting a protective effect against exposure to high levels of osmotic pressure. To understand these results, the relation between membrane physical state and structure of whole cells and osmotic shock tolerance of B. japonicum was studied. Membrane physical changes were evaluated by using 1,3-diphenyl-1,3,5-hexatriene (DPH) and Laurdan (6-dodecanoil-2-dimethylaminonaphtelene) as probes. The results showed that the membrane of B. japonicum was subjected to a progressive phase transition from the liquid-crystalline to the gel phase during cooling between 28 and 4 degrees C. Accordingly, under isotonic conditions, the Laurdan GP spectra showed that, in the range 12-28 degrees C, membrane lipids were in the liquid-crystalline phase, and in a gel phase at 4 degrees C. The study of the variation in anisotropy of DPH revealed that cooling cells before the hyperosmotic treatment could induce opposite effects to the fluidizing effect of the hyperosmotic shock. Cell resistance was finally related to modifications of the membrane structure depending on combined effects of cooling and dehydration.
Some important and essential features of absorption and fluorescence spectra of prodan in homogeneous and binary mixes are studied. According to results obtained from experimental and quantum-chemical researches we show that the absorption spectrum of prodan in nonpolar solvent within 25,000-50,000 cm(-1) is formed by eight electronic transitions. Quantum-chemical calculations are performed in the geometry of both the ground and exited states of prodan. The rate constants of photoprocesses and the quantum yield of fluorescence are determined for the prodan and its complexes with water. A dramatic shift of the fluorescence band at changing from nonpolar solvent to isopropyl alcohol and water is explained. The roles of general solvent effects and specific interactions are separated. According to values of molecular electrostatic potential and charges on atoms the centers of possible interaction of prodan with a solvent are obtained. Possible models of prodan complexes in water are offered. The results of quantum-chemical calculation for offered complexes of prodan in water are compared with those for the free prodan molecule. The presence of the second band (about 24,000 cm(-1)) in fluorescence spectra of prodan in isopropyl (ethyl) alcohol-water solvents is explained.