PubMed · 13289249
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L ROSENTHALER. 1955. [Bromacidometric method. IX].. https://pubmed.ncbi.nlm.nih.gov/13289249/
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Quenched phosphorescence detection of camphorquinone in cyclodextrin-based electrokinetic chromatography provides very favorable detection limits, i.e., 7 x 10(-)(7) M, 3 orders of magnitude lower than conventional UV absorption detection at 200 nm. The detection is based on the dynamic quenching by the analyte of the strong phosphorescence emission of brominated naphthalenesulfonate, under deoxygenated buffer solution conditions. This approach has been used to detect (1S)-(+)- and (1R)-(-)-camphorquinone after enantiomeric separation by CE. Although the use of the negatively charged carboxymethyl beta-cyclodextrin (CM-beta-CD) alone was not successful, the addition of a second, neutral cyclodextrin, alpha-CD, provided an adequate enantiomeric separation of camphorquinone. Using 25 mM borate buffer (pH 8.5) with 10 mM CM-beta-CD and 20 mM alpha-CD (applied voltage 20 kV, ambient temperature), the enantiomeric separation was performed in approximately 14 min. The chiral method was applied to monitor the stereoselectivity of the biotransformation of a racemic mixture of camphorquinone by yeast. It was found that the enantiomeric ratio calculated from the peak areas in the electropherogram (RSD = 5%) after 24 h of incubation decreased from 0.92 for the control solution (culture medium without yeast) to 0.24 for the culture medium; a similar ratio of 0.25 was observed for cell extract solutions. Therefore, racemic camphorquinone is enantioselectively degraded by yeast, the biodegradation of (1S)-(+)-camphorquinone being faster than that of the (1R)-(-)-enantiomer.
Polybrominated diphenyl ethers (PBDE) are commonly used flame retardants. During the past years, concerns have increased due to their occurrence in the environment and humans. In general, the concentrations of lower brominated (tetra-penta) diphenyl ethers in biota exceed those of the most heavily used product, decabromodiphenyl ether (DecaBDE). In this study, the photolytic debromination of DecaBDE has been investigated in order to study the formation of lower brominated diphenyl ethers. The time course of photolysis of DecaBDE was studied in toluene, on silica gel, sand, sediment and soil using artificial sunlight and on the natural matrices (sediment, soil, sand) also using natural sunlight. DecaBDE was photolytically labile and formed debromination products in all matrices studied. Nona- to tetraBDEs were formed as well as some PBDFs. The half-lives in toluene and on silica gel were less than 15 min, and half-lives on other matrices ranged between 40 and 200 h. No differences were seen in the debromination pattern of BDE congeners sequentially formed in the different matrices or under different light conditions. However, the debromination rates were strongly dependent on the matrix with longer half-lives on natural matrices than artificial ones.
Tryptophan residues are thought to play special roles in integral membrane proteins, anchoring transmembrane alpha-helices into the lipid bilayer. We have studied the effect of mutating the five Trp residues in the diacylglycerol kinase (DGK) of Escherichia coli to Leu residues. The fluorescence emission maxima for DGK and a variety of Trp mutants in bilayers of dioleoylphosphatidylcholine [di(C18:1)PC] are all centered at ca. 327 nm, suggesting that all five Trp residues are located close to the glycerol backbone region of the bilayer. This is also consistent with fluorescence quenching experiments, measuring the separation between the Trp residues and the bromine atoms in a bilayer of dibromostearoylphosphatidylcholine. Mutation of Trp residues in DGK was found to have significant effects on activity for DGK reconstituted into bilayers of di(C18:1)PC containing 30 mol % 1,2-dihexanoylglycerol (DHG). Of the mutants containing a single Trp residue, only that containing Trp-112 was found to give active protein. The presence of both Trp-25 and Trp-112 gave higher activity than Trp-112 alone. Trp-25 and Trp-112 are the most important Trp residues in DGK as far as activity is concerned. Effects of mutations on K(m) for DHG were generally greater than effects on v(max). The activity of wild-type and mutant DHGs reconstituted into bilayers of phosphatidylcholines was sensitive to the chain length of the phospholipid, with highest activities for chain lengths of C18 or C20 and lower activities in phosphatidylcholines with shorter or longer chains. Compared to wild-type DGK, the Trp mutants were less affected by long-chain phosphatidylcholines but more affected by short-chain phospholipids. In mutants lacking Trp-25, low activities in short-chain phospholipids followed from a decrease in v(max) compared to wild type, combined with an increase in K(m) value for DHG, as observed in the wild type. It is suggested that Trp-25 plays a role in maintaining the alignment of ATP and DHG at the active site. Fluorescence emission spectra for the Trp mutants do not change significantly with changing fatty acyl chain length from C14 to C24, showing efficient hydrophobic matching between DGK and the surrounding lipid bilayer. It is suggested that hydrophobic matching is achieved by tilting of the transmembrane alpha-helix or rotation of residues at the ends of the helices about the Calpha-Cbeta bond linking the residue to the helix backbone. As well as any structural effects, the presence of Trp residues in DGK has a clear effect on thermal stability.