ABSTRACT
Quinohemoprotein-cytochrome c complex alcohol dehydrogenase (ADH) of acetic acid bacteria consists of three subunits, of which subunit I contains pyrroloquinoline quinone (PQQ) and heme c, and subunit II contains three heme c components. The PQQ and heme c components are believed to be involved in the intramolecular electron transfer from ethanol to ubiquinone. To study the intramolecular electron transfer in ADH of Acetobacter methanolicus, the redox potentials of heme c components were determined with ADH complex and the isolated subunits I and II of A. methanolicus, as well as hybrid ADH consisting of the subunit I/III complex of Gluconobacter suboxydans ADH and subunit II of A. methanolicus ADH. The redox potentials of hemes c in ADH complex were -130, 49, 188, and 188 mV at pH 7.0 and 24, 187, 190, and 255 mV at pH 4.5. In hybrid ADH, one of these heme c components was largely changed in the redox potential. Reduced ADH was fully oxidized with potassium ferricyanide, while ubiquinone oxidized the enzyme partially. The results indicate that electrons extracted from ethanol at PQQ site are transferred to ubiquinone via heme c in subunit I and two of the three hemes c in subunit II. Copyright 1998 Elsevier Science B.V.
ABSTRACT
A method for the determination of seven chlorinated phenols, including those in the US Environmental Protection Agency list of priority pollutants, in drinking water is described. Solid-phase extraction on various alkylsilica bonded phases such as phenyl-, octyl- and octadecylsilica was used for sample preconcentration. The dependences of recovery on the eluent volume, sample pH and sample volume were investigated for all the sorbents in order to find the optimum sorbent. Octadecylsilica was found to be the most efficient sorbent. The sample pH was adjusted to 5.0 and, after concentration, the analytes were eluted with 1.2 cm3 of acetonitrile-0.012 mol dm-3 phosphoric acid (9 + 1). The extract was submitted to reversed-phase high-performance liquid chromatography with acetonitrile-0.007 mol dm-3 phosphoric acid (51 + 49) as the eluent and ultraviolet detection at 225 nm. Recoveries after 28 d of storage in a refrigerator at 3 degrees C were also studied. The results were found to agree with those before storage. A comparison between Bakerbond C18 and Separcol C18 is presented. The results obtained were comparable for both types of octadecylsilica. The recoveries of seven chlorinated phenols were higher than 88%. Extracting a 1 dm3 water sample, a detection limit of 2.6 micrograms dm-3 was determined for 2-chlorophenol and detection limits between 0.12 and 0.38 microgram dm-3 were obtained for the other six chlorinated phenols.
