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S Laakso

Publications and source records attributed to S Laakso.

32 records · Page 2Linked to original sources
PubMed1987

Colorimetric determination of beta-cyclodextrin: two assay modifications based on molecular complexation of phenolphtalein.

The decolorization of phenolphtalein upon complexation to cyclodextrins was studied to measure beta-cyclodextrin concentrations. Several factors possibly affecting the self-life of the dye were tested. By making the assays in 0.1 M NaCO3 solution beta-cyclodextrin concentrations down to 6 microM (SNR = 2) could be determined while the practical assay range reached up to 0.06 mM. In this form the method was unaffected by acyclic oligosaccharides and directly applicable to cyclodextrin assays in complex starch hydrolyzates. The method was further modified to be used in a flow-injection analyzator and the results were comparable to those obtained by HPLC analyses after prepurification of the samples.

Autoanalysis↗
PubMed1986

Inhibition of soybean lipoxygenase-1 by 10-butyryl substituted 1,8-dihydroxy-9-anthrone (butantrone).

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.

Anthracenes↗
PubMed1984

Inhibition of lipid peroxidation by casein. Evidence of molecular encapsulation of 1,4-pentadiene fatty acids.

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.

Caseins↗
PubMed1984

Determination of cis,cis-methylene interrupted polyunsaturated fatty acids in aqueous solutions by lipoxygenase chemiluminescence.

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).

Arachidonic Acids↗
PubMed1983

A microassay of O2 concentrations based on oxygen-induced chemiluminescence in anaerobic lipoxygenase reactions.

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.

Anaerobiosis↗
PubMed1982

A specific arginase-based assay for L-canavanine in leguminous plants.

A convenient method for the analysis of free L-canavanine in leguminous plants is described. Canavanine was specifically hydrolyzed to canaline and urea by the enzyme arginase (EC 3.5.3.1). The resulting amino-oxy functions of canaline were measured based on their ability to bleach the yellow colour of pyridoxal 5'-phosphate. Canavanine in the seeds of Canavalia ensiformis was determined with this method.

Arginase↗
PubMed1977

Altered regulation of macromolecular synthesis in methionine-inhibited cultures of Pseudomonas fluorescens UK1.

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.

Kinetics↗
PubMed1976

Methionine degradation by Pseudomonas fluorescens UK1 and its methionine-utilizing mutant.

Pseudomonas fluorescens UK1, and a mutant derived from it that can use methionine as its sole source of carbon and nitrogen, were used to study methionine degradation. Radioactive 2-oxomethionine, 2-oxobutyric acid and carbon dioxide comprised 95% of [I-14C]methionine consumed by the mutant. Demethiolating activity was detected in both strains when they were grown with methionine. The ability to grow on methionine depended on the decarboxylation of 2-oxobutyric acid derived from it. This decarboxylating activity was lost if the growth media contained an additional carbon source. No evidence was obtained for the operation of the cystathionine pathway.

Butyrates↗