Cytochrome c oxidation by the electron transport fraction of Azotobacter vinelandii

The spectrophotometric oxidation of horse heart ferrocytochrome c was examined by use of the particulate electron transport fraction (R(3)) of Azotobacter vinelandii strain O. Unlike cytochrome c, purified preparations of native Azotobacter cytochromes c(4) + c(5) were oxidized only slowly by the electron transport fraction. The oxidation of mammalian cytochrome c proceeded at an appreciable rate and displayed "apparent" first-order kinetics at a pH optimum of 9.0 with tris(hydroxymethyl)aminomethane-chloride buffer. The calculated V(max) value was 0.22 mumole of cytochrome c oxidized per min per mg of protein (25 C) and a K(m) value for cytochrome c of 2.3 x 10(-5)m was obtained. Ferricytochrome c was a "strict" competitive inhibitor for this oxidation. Cytochrome c oxidation by the Azotobacter electron transport system was markedly sensitive to cyanide, azide, and hydroxylamine, although carbon monoxide inhibition could not be demonstrated. It was sensitive also to high concentrations of phosphate, ethylenediaminetetraacetate, and some metal cations. "Aging" or prolonged storage of the Azotobacter R(3) fraction, at 4 C for 10 days, resulted in a threefold increase in specific activity. The cytochrome c peroxidase type of reaction did not occur with the R(3) electron transport fraction.     

纤维二糖脱氢酶抑制酚型化合物聚合及促进木素降解的研究

裂褶菌纤维二糖脱氢酶（ＣＤＨ）可以氧化纤维二糖并还原多种物质,催化的是一双底物双产物反应,符合乒乓反应机制,在电子供体纤维二糖存在下,ＣＤＨ可以还原由豆壳过氧化物酶（ＳＨＰ）氧化多种芳香化合物所生成的产物,ＳＨＰ氧化１－羟基苯丙三唑（１－ｈｙｄｒｏｘｙｂｅｚｏｔｒｉａｚｏｌｅ,ＨＢＴ）生成的产物对ＳＨＰ有失活作用,而在纤维二糖存在下,ＣＤＨ可以还原该氧化产物从而阻止其对酶的失活作用,ＣＤＨ可以抑制     

抗坏血酸对酵母蔗糖酶的激活动力学研究

采用甲苯自溶法从鲜酵母中提取了蔗糖酶,并用乙醇分级及ＤＥＡＥ－纤维素柱层析进行了纯化,用ＰＡＧ凝胶电泳作了纯度鉴定,在ｐＨ５．０,３０℃条件下进行了酶反应,用双倒数作图法测出其Ｋｍ＝２．１×１０－２ｍｏｌ／Ｌ,Ｖｍａｘ＝０．２６（每分钟的光密度值）．在此系统中,加入不同浓度的抗坏血酸（Ｖｉｔ．Ｃ）,发现其具有激活作用并存在量效关系．双倒数作图显示：酶的表观Ｖｍａｘ（Ｖｐ）随抗坏血酸浓度的增加而增大,但其表观Ｋｍ（Ｋｐ）不变（Ｋｐ＝Ｋｍ）．经实验结果分析,推论出抗坏血酸激活作用的酶促反应方程式,并推导出反应速度公式     

Removal of estrogenic activity from endocrine-disrupting chemicals by purified laccase of Phlebia tremellosa

A white-rot basidiomycete, Phlebia tremellosa, produced a laccase that showed increased activity during degradation of phthalates. A laccase was purified through the ion exchange chromatography and preparative gel electrophoresis, and the estimated molecular weight was 75 kDa. The optimum pH and temperature of the purified laccase was pH 4.0 and 20 degrees C, respectively. The K(m) value of the enzyme was 55.7 microM, and the V(max) was 0.0541 OD min(-1) U(-1) for o-tolidine. Purified laccase reduced the estrogenic activity of four different endocrine-disrupting chemicals. However, this effect was reduced by a laccase inhibitor, kojic acid, which confirmed that the laccase was involved in the removal of estrogenic activity.     

Laccase catalysed oxidation of syringic acid: calorimetric determination of kinetic parameters

Isothermal titration calorimetry (ITC) was used to study the oxidation of syringic acid by laccases from two different sources: Galerina sp. HC1 and Trametes versicolor. Total molar heat of reaction with both enzymes was similar (230 kJ/mol for Galerina laccase and 233 kJ/mol for Trametes laccase), and was independent of syringic acid concentration. The kinetic parameters of the reaction were calculated from the single injection assay by applying the nonlinear least squares fitting (NLSF) of experimental data to the Michaelis-Menten equation. Higher values for V(max) were obtained with Galerina sp. laccase, whereas K(m) values were comparable for the two enzymes.     

Oxidation of 1-hydroxybenzotriazole by laccase and lignin peroxidase

A method to measure laccase and lignin peroxidase (LiP) activity at 408 nm (402–410 nm) using 1-hydroxybenzotriazole (HBT) was developed. The assay can be performed either as a kinetic measurement or as a stopped reaction using 5 mM Na-azide which improves the spectrum. Only white-rot fungal laccases and LiP were found to oxidize HBT to give shoulders or peaks at 402-410 nm. Phanerochaete and Phlebia manganese peroxidases did not give absorbance increase at 402–410 nm. © Rapid Science Ltd. 1998     

Purification and regulatory properties of phosphoribulokinase from Hydrogenomonas eutropha H 16

1. Phosphoribulokinase was purified 286-fold from extracts of autotrophically grown cells. 2. The enzyme had a molecular weight of 237000 and showed a pH optimum of 9.0 in both crude extracts and purified preparation. MgCl(2) was required for activity; full activation was obtained at 5mm-MgCl(2) and the K(m) was approx. 0.5mm. 3. The ATP-saturation curve was sigmoidal and the degree of positive co-operativity increased at higher MgCl(2) concentrations. The ATP-binding sites appeared to be non-interacting at low ribulose 5-phosphate concentrations. 4. Lineweaver-Burk plots for ribulose 5-phosphate showed abrupt transitions between apparently linear sections. The apparent K(m) and V(max.) values increased with increasing concentrations of ribulose phosphate. The transitions may be explained by a sequence of negative and positive co-operativity in the catalytic rate constants. 5. Phosphoribulokinase activity was inhibited by AMP and phosphoenolpyruvate and was activated by NADH. The presence of AMP or phosphoenolpyruvate increased s(0.5) (substrate concentration required for half-maximal velocity) for both ribulose 5-phosphate and ATP but V(max.) was not changed. The sigmoidicity of the ATP-saturation curve increased in the presence of AMP but was not affected by phosphoenolpyruvate. The transitions in the ribulose 5-phosphate-saturation curves were more abrupt in the presence of either inhibitor. NADH lowered the s(0.5) for both ribulose 5-phosphate and ATP. The activator did not affect the degree of positive co-operativity between ATP-binding sites, but the ribulose 5-phosphate-binding sites appeared to be non-interacting in its presence. 6. A sequence of positive and negative co-operativity in the interactions of AMP-binding sites was suggested by the Hill plots. In the presence of NADH (and phosphoenolpyruvate) the sensitivity to inhibition by AMP was less below a certain AMP concentration and increased above that concentration. 7. Examination of the interactions between ligands indicated that phosphoribulokinase can be regulated effectively by changes in effector concentrations similar to those reported to occur in vivo.     

Complex-formation between cytochrome c and cytochrome c peroxidase. Kinetic studies

1. The kinetics of ferrocytochrome c peroxidation by yeast peroxidase are described. Kinetic differences between the older and more recent preparations of the enzyme most probably arise from differences in intrinsic turnover rates. 2. The time-courses of cytochrome c peroxidation by the enzyme follow essentially first-order kinetics in phosphate buffer. Deviations from first-order kinetics occur in acetate buffer, and are due to a higher enzymic turnover rate in this medium accompanied by a greater tendency to autocatalytic peroxidation of cytochrome c. 3. The kinetics of ferrocytochrome c peroxidation by yeast peroxidase are interpreted in terms of a mechanism postulating formation of reversible complexes between the peroxidase and both reduced and oxidized cytochrome c. Formation of these complexes is inhibited at high ionic strengths and by polycations. 4. Oxidized cytochrome c can act as a competitive inhibitor of ferrocytochrome c peroxidation by peroxidase. The K(i) for ferricytochrome c is approximately equal to the K(m) for ferrocytochrome c and thus probably accounts for the observed apparent first-order kinetics even at saturating concentrations of ferrocytochrome c. 5. The results are discussed in terms of a possible analogy between the oxidations of cytochrome c catalysed by yeast peroxidase and by mammalian cytochrome oxidase.     

Deuterium isotope effects for the oxidation of 1-methyl-3-phenyl-3-pyrrolinyl analogues by monoamine oxidase B

The parkinsonian inducing agent, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), is a cyclic tertiary allylamine exhibiting good monoamine oxidase B (MAO-B) substrate properties. MAO-B catalyzes the ring alpha-carbon 2-electron bioactivation of MPTP to yield the 1-methyl-4-phenyl-2,3-dihydropyridinium species (MPDP(+)). The corresponding 5-membered ring MPTP analogue, 1-methyl-3-phenyl-3-pyrroline, also undergoes MAO-B-catalyzed oxidation to give the 2-electron oxidation product, 1-methyl-3-phenylpyrrole. Here we report the kinetic deuterium isotope effects on V(max) and V(max)/K(m) for the steady-state oxidation of 1-methyl-3-phenyl-3-pyrroline and 1-methyl-3-(4-fluorophenyl)-3-pyrroline by baboon liver MAO-B, using the corresponding pyrroline-2,2,4,5,5-d(5) analogues as the deuterated substrates. The apparent isotope effects for the two substrates were 4.29 and 3.98 on V(max), while the isotope effects on V(max)/K(m) were found to be 5.71 and 3.37, respectively. The values reported for the oxidation of MPTP by bovine liver MAO-B with MPTP-6,6-d(2), as deuterated substrate, are (D)(V(max))=3.55; (D)(V(max)/K(m))=8.01. We conclude that the mechanism of the MAO-B-catalyzed oxidation of pyrrolinyl substrates is similar to that of the tetrahydropyridinyl substrates and that a carbon-hydrogen bond cleavage step is, at least partially, rate determining.     

Attributes of atmospheric carbon monoxide oxidation by Maine forest soils

CO, one of the most important trace gases, regulates tropospheric methane, hydroxyl radical, and ozone contents. Ten to 25% of the estimated global CO flux may be consumed by soils annually. Depth profiles for (14)CO oxidation and CO concentration indicated that CO oxidation occurred primarily in surface soils and that photooxidation of soil organic matter did not necessarily contribute significantly to CO fluxes. Kinetic analyses revealed that the apparent K(m) was about 18 nM (17 ppm) and the V(max) was 6.9 micromol g (fresh weight)(-1) h(-1); the apparent K(m) was similar to the apparent K(m) for atmospheric methane consumption, but the V(max) was more than 100 times higher. Atmospheric CO oxidation responded sensitively to soil water regimes; decreases in water content in initially saturated soils resulted in increased uptake, and optimum uptake occurred at water contents of 30 to 60%. However, extended drying led to decreased uptake and net CO production. Rewetting could restore CO uptake, albeit with a pronounced hysteresis. The responses to changing temperatures indicated that the optimum temperature for net uptake was between 20 and 25 degrees C and that there was a transition to net production at temperatures above 30 degrees C. The responses to methyl fluoride and acetylene indicated that populations other than ammonia oxidizers and methanotrophs must be involved in forest soils. The response to acetylene was notable, since the strong initial inhibition was reversed after 12 h of incubation; in contrast, methyl fluoride did not have an inhibitory effect. Ammonium did not inhibit CO uptake; the level of nitrite inhibition was initially substantial, but nitrite inhibition was reversible over time. Nitrite inhibition appeared to occur through indirect effects based on abiological formation of NO.     

Properties of a halophil nicotinamide–adenine dinucleotide phosphate-specific isocitrate dehydrogenase. Preliminary studies of the salt relations and kinetics of the crude enzyme

The effects of chlorides on NADP-specific isocitrate dehydrogenase from Halobacterium salinarium were investigated. The enzyme is stabilized by potassium chloride and sodium chloride and this effect is discussed in relation to the Hill (1913) equation. Kinetics of the enzyme were studied within a range of concentrations of potassium chloride and sodium chloride. Apparent Michaelis constants for both substrates were affected by salt concentration, the effect being greater in sodium chloride than in potassium chloride. Minimal apparent Michaelis constants for both substrates were similar to the corresponding constants reported for yeast isocitrate dehydrogenase. V(max.) was maximal in each salt at a concentration of about 1m. The maximum was higher in sodium chloride than in potassium chloride. At salt concentrations above about 2.3m, the apparent V(max.) was lower in sodium chloride than in potassium chloride, and at salt concentrations below 0.75-1.0m, each salt behaved as a linear activator of the enzyme. Within this concentration range salt and NADP(+) acted competitively; the activation by salt was overcome at finite concentrations of NADP(+). At concentrations above about 1m, potassium chloride was a linear non-competitive inhibitor of the enzyme. Within the range 1.0-2.5m, sodium chloride was also a linear non-competitive inhibitor, but above 2.5m it caused more pronounced inhibition.     

Water activity and substrate concentration effects on lipase activity

Catalytic activity of lipases (from Rhizopus arrhizus, Canadida rugosa, and Pseudomonas sp. was studied in organic media, mainly diisopropyl ether. The effect of water activity (a(w)) on V(max) showed that the enzyme activity in general increased with increasing amounts of water for the three enzymes. This was shown both for esterification and hydrolysis reactions catalyzed by R. arrhizus lipase. In the esterification reaction the K(m) for the acid substrate showed a slight increase with increasing water activities. On the other hand, the K(m) for the alcohol substrate increased 10-20-fold with increasing water activity. The relative changes in K(m) were shown to be independent of the enzyme studied and solvent used. The effect was attributed to the increasing competition of water as a nucleophile for the acyl-enzyme at higher water activities. In a hydrolysis reaction the K(m) for the ester was also shown to increase as the water activity increased. The effect of water in this case was due to the fact that increased concentration of one substrate (water), and thereby increased saturation of the enzyme, will increase the apparent K(m) of the substrate (ester) to be determined. This explained why the hydrolysis rate decreased with increasing water activity at a fixed, low ester concentration. The apparent V(max) for R. arrhizus lipase was similar in four of six different solvents that were tested; exceptions were toulene and trichloroethylene, which showed lower values. The apparent K(m) for the alcohol in the solvents correlated with the hydrophobicity of the solvent, hydrophobic solvents giving lower apparent K(m). (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 798-806, 1997.     

d-Glucose Transport System of Zymomonas mobilis

The properties of the d-glucose transport system of Zymomonas mobilis were determined by measuring the uptake of nonmetabolizable analogs (2-deoxy-d-glucose and d-xylose) by wild-type cells and the uptake of d-glucose itself by a mutant lacking glucokinase. d-Glucose was transported by a constitutive, stereospecific, carrier-mediated facilitated diffusion system, whereby its intracellular concentration quickly reached a plateau close to but not above the external concentration. d-Xylose was transported by the d-glucose system, as evidenced by inhibition of its uptake by d-glucose. d-Fructose was not an efficient competitive inhibitor of d-glucose uptake, indicating that it has a low affinity for the d-glucose transport system. The apparent K(m) of d-glucose transport was in the range of 5 to 15 mM, with a V(max) of 200 to 300 nmol min mg of protein. The K(m) of Z. mobilis glucokinase (0.25 to 0.4 mM) was 1 order of magnitude lower than the K(m) for d-glucose transport, although the V(max) values for transport and phosphorylation were similar. Thus, glucose transport cannot be expected to be rate limiting at concentrations of extracellular glucose normally used in fermentation processes, which greatly exceed the K(m) for the transport system. The low-affinity, high-velocity, nonconcentrative system for d-glucose transport described here is consistent with the natural occurrence of Z. mobilis in high-sugar environments and with the capacity of Z. mobilis for rapid conversion of glucose to metabolic products with low energetic yield.     

Desferrioxamine enhances the reactivity of vanadium (IV) and vanadium (V) toward ferri- and ferrocytochrome c.

Ligands, especially desferrioxamine, affect the rate at which vanadium reduces or oxidizes cytochrome c. Whether reduction or oxidation occurs, and how fast, depends on the nature of the ligand, the state of reduction of the vanadium, the pH (6.0, 7.0, or 7.4), and the availability of oxygen. In general, oxidation of ferrocytochrome c was favored by (1) low pH, (2) an oxidized state of the vanadium, (3) the presence of oxygen, and (4) more strongly binding ligands (desferrioxamine much greater than histidine = ATP greater than EDTA greater than albumin greater than aquo). Thus, at pH 6.0, desferrioxamine accelerated the V(V)-catalyzed ferrocytochrome c oxidation 160-fold aerobically, and 3500-fold anaerobically. In general, strongly binding ligands slowed oxidations, especially at higher pH. Desferrioxamine was unique among the five ligands in that it not only accelerated oxidation of ferrocytochrome c at pH 6.0, but at pH 7.4 the redox balance shifted to the point where it paradoxically reduced ferricytochrome c. V(V) is an improbable electron donor, but desferrioxamine will reduce cytochrome c, and V(V) accelerates this process. Oxidation of cytochrome c by V(V):desferrioxamine was faster anaerobically, and reduction by V(IV):desferrioxamine was faster aerobically. Although V(V) did not oxidize ferrocytochrome c at pH 7.4, V(IV) did, provided oxygen and desferrioxamine were both present. V(IV):desferrioxamine almost completely reduced ferricytochrome c, and this reduction was followed by a slow, progressive oxidation. This latter oxidation of cytochrome c is mediated by active species generated in the reaction between V(IV):desferrioxamine and oxygen, because none of these reagents alone can induce oxidation at a comparable rate. The mediating species were transient, and generated in reactions with oxygen.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transport of monosaccharides in kidney-cortex cells

1. The aerobic transport of d-glucose and d-galactose in rabbit kidney tissue at 25 degrees was studied. 2. In slices forming glucose from added substrates an accumulation of glucose against its concentration gradient was found. The apparent ratio of intracellular ([S](i)) and extracellular ([S](o)) glucose concentrations was increased by 0.4mm-phlorrhizin and 0.3mm-ouabain. 3. Slices and isolated renal tubules actively accumulated glucose from the saline; the apparent [S](i)/[S](o) fell below 1.0 only at [S](o) higher than 0.5mm. 4. The rate of glucose oxidation by slices was characterized by the following parameters: K(m) 1.16mm; V(max.) 4.5mumoles/g. wet wt./hr. 5. The active accumulation of glucose from the saline was decreased by 0.1mm-2,4-dinitrophenol, 0.4mm-phlorrhizin and by the absence of external Na(+). 6. The kinetic parameters of galactose entry into the cells were: K(m) 1.5mm; V(max) 10mumoles/g. wet wt./hr. 7. The efflux kinetics from slices indicated two intracellular compartments for d-galactose. The galactose efflux was greatly diminished at 0 degrees , was inhibited by 0.4mm-phlorrhizin, but was insensitive to ouabain. 8. The following mechanism of glucose and galactose transport in renal tubular cells is suggested: (a) at the tubular membrane, these sugars are actively transported into the cells by a metabolically- and Na(+)-dependent phlorrhizin-sensitive mechanism; (b) at the basal cell membrane, these sugars are transported in accordance with their concentration gradient by a phlorrhizin-sensitive Na(+)-independent facilitated diffusion. The steady-state intracellular sugar concentration is determined by the kinetic parameters of active entry, passive outflow and intracellular utilization.     

Purification and characterization of cytochrome c-553 from Helicobacter pylori

Helicobacter pylori, a microaerophilic Gram-negative spiral bacterium residing in the human stomach, contains a small size soluble cytochrome c. This cytochrome c was purified from the soluble fraction of H. pylori by conventional chromatographies involving octyl-cellulose and CM-Toyopearl. Its reduced form gave an alpha absorption band at 553 nm, and thus the cytochrome was named H. pylori cytochrome c-553. The cytochrome, giving a band below 10,000 Da upon SDS-PAGE, was determined to have a mass of 8,998 by time of flight mass spectroscopy. Its N-terminal peptide sequence was TDVKALAKS---, indicating that the nascent polypeptide was cleaved to produce a signal peptide of 19 amino acid residues and a mature protein composed of 77 amino acid residues. The cb-type cytochrome c oxidase oxidized ferrocytochrome c-553 of this bacterium actively (V(max) of about 250 s(-1)) with a small K(m) (0.9 microM). Analysis of the effect of the salt concentration on the oxidase activity indicated that oxidation of cytochrome c-553 is highly inhibited under high ionic conditions. The amino acid sequence of H. pylori cytochrome c-553 showed the closest similarity to that of Desulfovibrio vulgaris cytochrome c-553, and these sequences showed a weak relationship to that of the cytochrome c(8)-group among class I cytochromes c.     

Biosynthetic Pathway of Thiamine Pyrophosphate: a Special Reference to the Thiamine Monophosphate-Requiring Mutant and the Thiamine Pyrophosphate-Requiring Mutant of Escherichia coli

alpha-Isopropylmalate synthase, the first specific enzyme in leucine biosynthesis, was purified approximately 100-fold from extracts of Saccharomyces sp. (strain 60615), the most effective step being specific elution with the feedback inhibitor leucine from a hydroxyapatite column. In the early steps of purification, special care was taken to protect the synthase against proteolytic activities. The apparent molecular weight of the enzyme as determined from gel filtration on a calibrated column was 137,000 in the absence and 121,000 in the presence of leucine. Inhibition by leucine was specific and strongly pH-dependent, with the leucine concentration necessary for half-maximal inhibition increasing about 10-fold as the pH increased from 7.5 to 8.5. Within this pH range, catalytic activity remained almost unchanged. The apparent K(m) values for the two substrates were found to be 16 mum for alpha-ketoisovalerate and 9 mum for acetyl-coenzyme A. K(+) was required for full activity, the apparent K(a) value being 2 mm. Leucine inhibition was of the mixed type, resulting in decreased V(max) and increased apparent K(m) values forboth substrates. Whereas no cooperative effects were observed with either substrate, positive cooperativity was seen with leucine in the presence of saturating substrate concentrations. Leucine and, to a lesser extent, alpha-ketoisovalerate stabilized the purified enzyme against heat-inactivation. The presence of acetyl-coenzyme A, on the other hand, accelerated the inactivation. In subsequent experiments, coenzyme A was recognized as the actual inactivating ligand, being effective even at lower temperatures and in concentrations which were estimated to be in the range of the enzyme concentration.     

Anion and ionic strength effects upon the oxidation of cytochrome c by cytochrome c oxidase

Citrate and other polyanion binding to ferricytochrome c partially blocks reduction by ascorbate, but at constant ionic strength the citrate-cytochrome c complex remains reducible; reduction by TMPD is unaffected. At a constant high ionic strength citrate inhibits the cytochrome c oxidase reaction competitively with respect to cytochrome c, indicating that ferrocytochrome c also binds citrate, and that the citrate-ferrocytochrome c complex is rejected by the binding site at high ionic strength. At lower ionic strengths, citrate and other polyanions change the kinetic pattern of ferrocytochrome c oxidation from first-order towards zero-order, indicating preferential binding of the ferric species, followed by its exclusion from the binding site. The turnover at low cytochrome c concentrations is diminished by citrate but not the Km (apparent non-competitive inhibition) or the rate of cytochrome a reduction by bound cytochrome c. Small effects of anions are seen in direct measurements of binding to the primary site on the enzyme, and larger effects upon secondary site binding. It is concluded that anion-cytochrome c complexes may be catalytically competent but that the redox potentials and/or intramolecular behaviour of such complexes may be affected when enzyme-bound. Increasing ionic strength diminishes cytochrome c binding not only by decreasing the 'association' rate but also by increasing the 'dissociation' rate for bound cytochrome c converting the 'primary' (T) site at high salt concentrations into a site similar kinetically to the 'secondary' (L) site at low ionic strength. A finite Km of 170 microM at very high ionic strength indicates a ratio of K infinity m/K 0 M of about 5000. It is proposed that anions either modify the E10 of cytochrome C bound at the primary (T) site of that they perturb an equilibrium between two forms of bound c in favour of a less active form.     

Effect of pharmacologically selective antidepressants on serotonin uptake in rat platelets

We tested a hypothesis that a long-term administration of antidepressants acting through different primary biochemical mechanisms is associated with changes in the platelet serotonin (5-hydroxytryptamine, 5-HT) transport. Laboratory rats were administered norepinephrine reuptake inhibitors (desipramine, maprotiline), selective 5-HT reuptake inhibitor (citalopram), reversible monoamine oxidase inhibitor (moclobemide), and lithium (inositol monophosphatase inhibitor among others) during a 4-week period. Apparent kinetic parameters of platelet 5-HT transport were analyzed. Significant decrease in apparent Michaelis constant (K(M)) was found after the administration of all tested antidepressants except for desipramine. There was certain increase in maximal velocity (V(max)) values following the administration of desipramine, maprotiline, and citalopram; however, the all V(max) changes were not significant. V(max)/K(M) ratio representing limiting permeability at low extracellular concentrations of 5-HT was systematically increased in all the tested drugs, but significant changes were occurred only in maprotiline- and citalopram-treated rats. Adaptive changes in platelet 5-HT transport induced by citalopram were opposite to the acute inhibitory effect of this drug on 5-HT transporter activity. An increase in limiting membrane permeability for 5-HT could be included in the common adaptive effect of the long-term administration of antidepressants that differ in pharmacologic selectivity.     

Decolorization of aqueous solutions of disperse textile dyes by oxidoreductases

The potential of three oxidoreductases, a laccase preparation of Pleurotus sajor-caju PS-2001, horseradish peroxidase (HRP) and a microbial peroxidase (MP) was evaluated for the decolorization of disperse textile dyes (CI Disperse Red 343, CI Disperse Red 167 and CI Disperse Blue 148) used in polyester dyeing. Decolorization was studied in aqueous solutions varying in dye concentration, pH, temperature, enzyme concentration and the addition of mediators HBT and syringaldazine. The best conditions found for Disperse Red 343 with laccase, HRP and MP were: 15 mg L^?1 dye concentration, 50°C, pH 3.0 for laccase and pH 5.0 for peroxidases. Without mediator, the highest decolorizaton results (38.5% and 58.6%) were achieved with the highest tested concentrations of laccase (10 U mL^?1) and HRP (89.7 U mL^?1), respectively, but no significant difference in decolorization was found for the tested MP concentrations (29.9–89.7 U mL^‐1). HBT or syringaldazine increased decolorization with peroxidases significantly, but no effect was observed for the laccase. Decolorization of Disperse Red 167 (up to 15%) and Disperse Blue 148 (up to 25%) was much lower than of Disperse Red 343. With respect to enzyme concentration, the use of mediator and under the selected test conditions the laccase of P. sajor-caju PS-2001 turned out to be more efficient in disperse dye decolorization, than peroxidases HRP and MP.