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A high-performance liquid chromatographic method for the determination of plasma concentrations of erythromycin base and 2'-acetylerythromycin, an ester prodrug of erythromycin, is described. tert.-Butyl methyl ether extracts of 1-ml plasma samples (pH 10) were chromatographed on a C18 reversed-phase column. A three-electrode coulometric detector (oxidation potentials +0.65 and +0.85 V) was used for quantitation. Oleandomycin was used as an internal standard. The method has good precision and accuracy, is linear in the range 0.25-7.5 mg/l and has proved to be suitable for pharmacokinetic studies in humans. Correlation with a microbiological assay was satisfactory (r greater than or equal to 0.95), but the chromatographic method gave ca. 30% higher values.

The capability of cyclodextrins to form molecular inclusion complexes with linoleate appeared in a lipoxygenase-linoleate model reaction as inhibition of oxygenation. The inhibited rates were established instantaneously upon addition of the complexant and maintained until linoleate was exhausted. Total cessation of the reaction was not obtained with cyclodextrins. All these features were reproduced also in casein-inhibited reaction mixtures. Both casein and cyclodextrins protected linoleate also against autoxidation although they did not change free radical generation by xanthine oxidase or Fe2+ reactions. Since neither of the inhibitors affected the enzyme directly, casein may also act by forming linoleate complexes which via a standing equilibrium reduce the oxidizable monomer fatty acids and cause substrate-limited reaction rates. Comparisons at acidic and alkaline pH, in the presence of increasing amounts of the complexants, detergent and hydroperoxides supported this view.

Effects of high methionine concentrations on growth of Pseudomonas fluorescens UK1 are reported. The following phenomena were observed: (i) Immediate inhibition of growth for a period corresponding to approximately half a generation. Steady-state conditions of growth were no more attained. (ii) In spite of stringency of the macromolecular synthesis in this organism, simultaneously with the growth inhibition, the rate of labelled leucine incorporation into trichloroacetic acid (TCA)-insoluble material was reduced 60% while the rate of labelled uracil incorporation remained constant. (iii) The organism began to liberate methanethiol half a generation after the methionine supplement. Demethiolating activity increased linearly with the cell mass. It is concluded that the inhibition of growth is not due to the liberation of methanethiol from methionine but the amino acid is able to uncouple the mechanism coordinating protein and RNA synthesis in P. fluorescens UK1.

The preparation of chemiluminescence probes for assaying O2 concentrations in microsamples is described. This probe is based on an anaerobic lipoxygenase-linoleate system continuously generating reactive intermediates which in a spontaneous reaction with added O2 yield an excited species. The resulting chemiluminescence signals are highly reproducible upon repeated sample application and unaffected by even large variations in the contents of lipoxygenase-1 and linoleic acid. The linear assay range is between 0.25 and 25 nmol of O2. The assay system described is stable for 90 +/- 10 min, irrespective of the number of samples added, and the probe can be regenerated thereafter by adding linoleic acid.

10-Butyryl substituted 1,8-dihydroxyanthrone (butantrone) inhibited soybean lipoxygenase-1 irreversibly and more efficiently than its parent compound 1,8-dihydroxyanthrone (dithranol, anthralin) (IC50 values 0.090 mM and 1.1 mM, respectively). Intact butantrone rather than its hydrolysis product was the primary effector and the 10-butyryl moiety its site specific probe, probably directing the inhibitor to the proximity of the binding site of the lipid substrate/product.

The chemiluminescent reaction of luminol during lipoxygenase-catalyzed oxygenations was studied with the purpose of developing a specific luminometric assay for cis,cis-1,4-pentadiene fatty acids directly in aqueous solutions. The addition of picomole levels of either linoleic or arachidonic acids to reaction systems containing 0.04 mM luminol and 40 micrograms/ml of purified soybean lipoxygenase-1 gave light emission curves with a single sharp maximum. Under these conditions the peak heights were linearly dependent on the fatty acid concentration and the detection limit for both of the fatty acids was 2 pmol with a signal to noise ratio of 2. For maximum reproducibility of the assays a procedure for the proper quantitation of the enzyme was developed. The fact that the assay proved to be relatively interference-free was ascribed to the high molar enzyme/substrate ratio (above 1).