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Biomedical subjects

K Knobloch

Publications and source records attributed to K Knobloch.

At least 19 recordsLinked to original sources
PubMed2003

[Ross procedure with combined replacement of the ascending aorta: impact on autograft root function and distensibility].

BACKGROUND: The safety and effectiveness of combined aortic root autograft replacement in combination with ascending aorta replacement has been demonstrated recently. Replacement of the ascending aorta with a vascular prosthesis results in an increase in aortic root distension, and aortic root wall stress. In this study we aimed to assess the autograft root dimensions, distensibility, and autograft valve function in patients after Ross operation combined with replacement of the ascending aorta compared to patients who underwent Ross operation only. PATIENTS AND METHODS: Echocardiographic follow-up was performed on 28 patients after Ross operation with complete root replacement only (group R) and 12 patients who received an additional replacement of the ascending aorta (group R/A). The mean follow-up time was 24.9 +/- 17.2 months. Autograft root dimensions, root distensibility and valve function were assessed by echo-cardiography. The aortic root was measured at the level of the annulus, sinus of valsalva, and sinotubular junction. The distensibility was calculated as percent change of radius. RESULTS: The mean distensibility at the annulus level was higher in group R/A (18.4 +/- 6.8% vs 13.4 +/- 8.1%; p = 0.047); at the level of the sinus of valsalva and sinotubular junction no differences were observed. The autograft pressure gradient was within physiological limits in all patients. The majority of patients showed a competent autograft valve (group R: AI 0 degree; 83%, AI I degree; 14%, AI II degree; 3%; group R/A: AI 0 degree; 75%, AI I degree; 25%). CONCLUSIONS: Replacement of the ascending aorta with a non-compliant prosthesis does not effect root dimension, distensibility, and valve function.

Adult↗
PubMed2001

Differential effects of dofetilide, amiodarone, and class lc drugs on left and right atrial refractoriness and left atrial vulnerability in pigs.

OBJECTIVES: Antiarrhythmic drugs have been shown to prolong right atrial refractoriness while data on the left atrium are not available. In pigs we have observed shorter effective refractory periods (ERP) of the left compared with the right atrium associated with a much higher left atrial vulnerability for tachyarrhythmias. Since this could suggest a different distribution of repolarizing ion channels in left and right atrium, we investigated whether antiarrhythmic drugs blocking different ion channels have a differential effect on left and right atrial ERP and left atrial vulnerability. METHODS: In pentobarbital-anesthetized pigs (n=40) we measured and compared ERPs in both atria before and after different drugs with the S1-S2 extrastimulus method at three basic cycle lengths (BCL) and assessed the inducibility of atrial fibrillation/flutter (AF/AFL) by the premature S2 stimulus. RESULTS: At the three BCL tested (240/300/400 ms) baseline ERPs were shorter in left vs. right atrium (112+/-2/124+/-2/129+/-2 ms vs. 147+/-2/163+/-2/167+/-2 ms, P<0.001). Mostly non-sustained AF/AFL induced by the S2 extrastimulus was very frequent in the left (68%) and nearly absent in the right atrium (3%). Only amiodarone, 5 mg/kg i.v., which showed a balanced increase of left and right atrial ERP (29+/-5/33+/-4/35+/-3% vs. 30+/-5/35+/-5/42+/-7%), decreased the inducibility of AF/AFL significantly (-72%, P<0.01). Dofetilide, 10 microg/kg i.v., had a stronger effect on right than left atrial ERP (36+/-4/39+/-5/46+/-10% vs. 23+/-2/22+/-7/22+/-5%, P<0.05), while flecainide, 1 mg/kg i.v., prolonged left more than right atrial ERP (58+/-15/36+/-7/40+/-7% vs. 26+/-5/24+/-5/21+/-4%, P<0.05) similar to 1 mg/ kg of propafenone (46+/-5/45+/-7/32+/-10% vs. 17+/-4/21+/-5/ 25+/-8%, P<0.05). CONCLUSION: The shorter refractoriness of the left compared with the right atrium observed in pigs was associated with a high left atrial vulnerability for tachyarrhythmias, which was reduced only by amiodarone showing a balanced increase of left and right atrial ERP. Dofetilide was stronger on right atrial ERP, flecainide and propafenone on left atrial ERP. These differences suggest a differential distribution of repolarizing ion channels between left and right atrium with possible relevance for the antiarrhythmic efficacy of drugs.

Amiodarone↗
PubMed2000

Dihydro

[formula: see text] Treatment of o-propargylaryl nitrones with base provided 1,2-dihydro[c]benzazepin-3-ones in good yields. The straightforward transformation is explained on the basis of a multistep rearrangement involving conjugated allene-nitrones as precursors of a 1,7-dipolar electrocyclization process that is followed by further bond reorganizations.

Journal Article↗
PubMed1987

Inhibitory effects of essential oil components on growth of food-contaminating fungi.

The antifungal activity of several components of essential oils were evaluated using a paper-disk method. The substances investigated are structurally related to eugenol. Equimolar amounts were tested on more than ten fungal strains known to contaminate food. Iso-eugenol, cinnamaldehyde, carvacrol, eugenol and thymol revealed the strongest antifungal activity. The most resistant strain appeared to be Penicillium verrucosum var. cyclopium, and the most sensitive was P. viridicatum. Some of the structural effects were considered, including a free hydroxyl group in connection with an alkyl substituent which seemed to represent an especially active configuration of phenolic compounds and which rendered antimicrobial activity.

Food Contamination↗
PubMed1986

Purification and properties of a soluble inorganic pyrophosphatase from Rhodopseudomonas palustris.

A soluble inorganic pyrophosphatase from photolithoautotrophically grown Rhodopseudomonas palustris was purified to a state of apparent homogeneity applying high resolving liquid chromatography steps. Values of 65 500 and 64 500 were calculated for the relative molecular mass under non-dissociating conditions employing gel filtration and high-performance liquid chromatography, respectively. Dissociation sodium dodecyl sulfate gel electrophoresis resulted in a value of 32 000, indicating that the enzyme is composed of two subunits of equal molecular mass. Isoelectric focusing revealed a pI value of 4.7. The purified enzyme was specific for PPi and the activity was modified by divalent cations. Ca2+, Mn2+, Mg2+ and Co2+ were potent activators at a concentration ratio of [Me2+]/[PPi] less than 1. Ca2+ turned out to be the most potent activator. Free Me2+ was inhibitory on the PPiase activity. The (Me-PPi) complex is regarded as the functional substrate. Km and Ki values of the metal activation and inhibition were determined. An activation energy of Ea = 14.4 kJ/mol was derived from Arrhenius plots for the enzymatic reaction.

Calcium↗
PubMed1986

Kinetic characterization and partial purification of the membrane-bound inorganic pyrophosphatase from Rhodopseudomonas palustris.

A membrane-bound inorganic pyrophosphatase from Rhodopseudomonas palustris has been studied by kinetic analysis. The enzymatic activity was stimulated by Mg2+, and the (Mg-PPi) complex is regarded to be the functional substrate. Free Mg2+ revealed a significant influence on the membrane-bound PPiase activity. Kinetic data were determined at various fixed concentrations of free Mg2+. Mg2+ is proposed to act as an activator in two ways. It may interact with the enzyme directly, and may combine with PPi to yield the functional substrate Mg-PPi. Ca2+ revealed a non-competitive type of inhibition on the Mg2+-activated enzyme. The membrane-bound PPiase activity was firmly attached to the chromatophore membrane. To achieve an almost entire solubilization, both, Triton X-100 and high concentrations of Mg2+, had to be applied. An enrichment method along with stepwise lowering the concentrations of Triton X-100 and Mg2+ after the solubilization has been established. The solubilized and partially purified enzyme was stimulated by phospholipids while the influence of free Mg2+ was lost. Three different energies of activation as a function of temperature were derived from Arrhenius plots for the membrane-bound as well as for the solubilized PPiase activity.

Calcium↗
PubMed1986

Purification and properties of an acetate kinase from Rhodopseudomonas palustris.

An acetate kinase from the photolithoautotrophically grown purple bacterium Rhodopseudomonas palustris was purified to apparent homogeneity by use of high resolving liquid chromatography steps. The monomeric enzyme was characterized by a relative molecular mass of 46,500 and an isoelectric point of 4.9. There was an absolute requirement for divalent metal ions in the enzymatic reaction. Mg2+ and Mn2+ were the most activating cations. The acetate kinase used pyrimidine and purine nucleotides almost equally well as phosphoryl donors. The enzyme phosphorylated acetate, propionate, butyrate and isobutyrate. ATP and acetate revealed the lowest apparent Km values and seemed to act as the favoured substrates. The apparent Km values for ATP formation were considerable lower than those for the formation of acetyl phosphate. The activation energy Ea = 21 kJ/mol of the acetyl phosphate formation was determined by application of Arrhenius plots.

Acetate Kinase↗
PubMed1986

Purification and characterization of a phosphotransacetylase from Rhodopseudomonas palustris.

A phosphotransacetylase was purified to apparent homogeneity from photolithoautotrophically grown Rhodopseudomonas palustris by liquid chromatography methods. A 400-fold increase in specific activity could be achieved. The enzyme was characterized by a relative molecular mass of 54,500, an isoelectric point of 6.3 and the absence of dissociable subunits. The enzyme appeared very labile at elevated temperatures or in diluted solutions. The stability could be increased distinctly in case sulfate or ammonium ions were added to the enzyme solution. The activity also was influenced by inorganic salts. Potassium and ammonium ions activated the enzymatic reaction. Sulfate ions revealed an inhibitory influence. A strong substrate inhibition was found with coenzyme A as substrate. The Arrhenius plot revealed a discontinuity at 15 degrees C which most likely corresponds to a conformational change of the enzyme protein.

Acetyltransferases↗
PubMed1986

[Experimental studies of acute and chronic toxic effects of vinyl acetate].

In view of divergent opinions concerning MAC value for vinyl acetate, a study on acute and chronic inhalatory toxic effect of this compound on animals was carried out. The scope of the study included determination of CL50 value after Litchfield and Wilcoxon and 10-month exposure of animals to vinyl acetate at concentrations 10, 100 and 500 mg/m3, 5 days weekly, 5 hours daily. During 10-month experiment the animals were observed and body weight controlled. In addition, periodically some hematological examinations and biochemical of blood serum as well as histopathological examinations of inner organs were carried on. Post-mortally the weight of inner organs was determined. CL50 value determined on rats has amounted to 4100 ppm. In the study on chronic effect, the prevalence and the degree of intensity of the changes of the used by us indicators was the least in the group of animals exposed to vinyl acetate at concentration of 10 mg/m3. These changes were transient not involved reticulopenia and animals' body weight decrease. Histopathological examinations revealed some inflammatory changes in respiratory system both in control and exposed animals. Only planoepithelial metaplasia of bronchi was found exclusively in animals exposed to vinyl acetate at all concentrations used. The changes within liver were found only in animals exposed to vinyl acetate at concentration of 100 and 500 mg/m3. These changes involved fatty degeneration of hepatic parenchyma, proliferation and extension of smooth endoplasmatic reticulum and the changes within the biliary canaliculi. Taking the above results into account it seems that the lowest of the recommended in the world MAC value--10 mg/m3 may be accepted as the upper limit of the maximum admissible concentration for vinyl acetate.

Air Pollutants↗
PubMed1983

Kinetic studies on the membrane-bound and the purified coupling factor-ATPase from Rhodopseudomonas sphaeroides.

The activity of membrane-bound and purified ATPase (EC 3.6.1.3) was potentiated by several divalent cations. Highest rates of ATP hydrolysis were obtained when the activity was measured with the (cation-ATP)2- complex. Free ATP and free divalent cations in excess were found to be competitive inhibitors to the complex. The apparent Km (complex) values were lower than the Ki values for free ATP indicating that the (cation-ATP)2- complex is bound more tightly to the enzyme than the free ATP. Based on these results, a binding of the complex to the active site at two points is suggested, namely through the ATP and through the cation. Removal of the coupling factor from the membrane apparently caused conformational changes which resulted in a pronounced alteration of the kinetic parameters of ATPase activity. Whereas highest values in chromatophore-bound ATPase activity were observed in the presence of Mg2+, the purified enzyme became even more active in the presence of Ca2+. The Ki values for free ATP decreased upon solubilization of the enzyme. Free Mg2+ in excess was more inhibitory on the purified ATPase than Ca2+, while free Ca2+ in excess was more inhibitory on the membrane-bound enzyme if compared to Mg2+. Ki values for product inhibition by ADP and Pi were determined. Kinetic analyses of photophosphorylation activity revealed that the (cation-ADP)- complex is the functional substrate. The apparent Km values for the complex and for Pi were estimated. Excess of free cations and ADP inhibited competitively the phosphorylation. Ki(ADP), Ki(Ca2+), and Ki(Mg2+) were calculated by Dixon analyses.

Adenosine Diphosphate↗
PubMed1983

Characteristics and amino-acid composition of a c-type cytochrome in electron acceptor function during thiosulfate-linked photoautotrophic growth of Rhodopseudomonas palustris.

The purple bacterium Rhodopseudomonas palustris (Rhodospirillaceae) was grown in the light with thiosulfatee as the only electron source and HCO theta 3/CO2 as carbon requirement. During thiosulfat oxidation, photolithoautotrophically growing cells transferred the electrons enzymatically towards an endogenous, soluble cytochrome of type c. The cytochrome c in electron acceptor function was purified to homogeneity and appeared as a single protein band in a dodecyl sulfate disc gel electrophoresis. Its molecular mass was determined to be about 16000 Da and its pI value 10.0. The determination of its amino-acid composition revealed a long-chained cytochrome represented by more than 120 amino-acid residues with a characteristic content of lysine and a lack of tryptophan.

Amino Acids↗
PubMed1982

Purification and properties of the coupling-factor ATPases F1 from Rhodopseudomonas palustris and Rhodopseudomonas sphaeroides.

The coupling-factor ATPases from photosynthetically grown Rhodopseudomonas palustris and Rhodopseudomonas sphaeroides were purified by the same procedure to homogeneity. Gel chromatography on Sephacryl S-300 Superfine shortened the process of purification and improved its yield. Solubilization of the ATPase from both bacteria was found to be dependent on a specific sonication treatment of the cell suspensions, indicating a very weakly bound F1-ATPase in R. palustris. Depleted chromatophores could be restored in photophosphorylation and membrane-bound ATPase activities by adding the solubilized ATPase protein. The purified enzymes did not show a markedly trypsin-stimulated or dithiothreitol-stimulated activity. Isoelectric focusing and chromatofocusing revealed isoelectric points of 5.0 for both F1-ATPases. The molecular weights were determined by gel chromatography plus high-performance liquid chromatography. Hence, we calculated a molecular weight of 350000 for both F1-ATPases. Sodium dodecylsulfate/polyacrylamide gel electrophoresis revealed five subunits for both enzymes. Kinetic parameters, regarding substrate specificity, the effect of divalent cations, Km and Ki values for the membrane-bound and solubilized ATPases were determined.

Bacterial Proteins↗
PubMed1979

Effect of growth condition on enzymes of the citric acid cycle and the glyoxylate cycle in the photosynthetic bacterium Rhodopseudomonas palustris.

The enzymes of the citric acid and glyoxylate cycles as well as RuBP4 carboxylase were measured in cell-free extracts from Rhodopseudomonas palustris after growth under chemoheterotrophic, photoheterotrophic and photolithotrophic conditions. Although the citric acid cycle was found to be complete under all growth conditions, significant differences in certain enzyme activities occurred as a function of the different energy sources applied. The glyoxylate cycle also was complete under all growth conditions with highest isocitrate lyase activity seen after photoheterotrophic growth on acetate. Photo- and chemoheterotrophic growth on malate reduced the isocitrate lyase. The activity was not repressed further by photolithotrophic growth on thiosulfate. RuBP carboxylase activity, present under photolithotrophic conditions, was repressed by chemoheterotrophic growth but was not decreased by the presence of organic substrates during photoheterotrophic growth.

Aerobiosis↗
PubMed1979

Conduction velocity in the peripheral nerves of rats with chronic carbon disulphide neuropathy.

Effects of carbon disulphide (CS2) on conduction velocity in sciatic and tibial nerve were investigated in rats exposed to CS2 vapour at concentrations of 0.9 mg/l or 1.6 mg/l of air for periods of 1.5, 3, 6, 9 and 12 months. The conduction velocity was measured on the day following each exposure period, and again, three and six months after the last day of exposure. The majority of exposed rats showed a reduction in conduction velocity on the day after exposure: the extent of this reduction was dependent on the CS2 concentration and the duration of exposure. Exposure for 1.5 months to 1.6 mg CS2/l produced temporary and fully reversible impairment of conduction velocity. Increased exposure to CS2 (3,6 or 9 months at 1.6 mg/l; 6 or 12 months at 0.9 mg/l CS2 in air) caused a reduction in velocity which was only partially reversible.

Action Potentials↗
PubMed1979

[Evaluation of acute toxic effect of 3-cyanopyridine].

General acute toxicity, irritating, and allergic effects of 3-cyanpyridine were studied. LD50 after oral administration amounts to 1185 mg/kg of body weight, 3-cyanpyridine is absorbed through the intact skin: administration of 3-cyanpyridine solution into rabbit skin caused death of animals. Histopathologic studies showed reversible liver and kidney injuries after single administration of lethal and sublethal doses. 3-cyanpyridine significantly irritates damaged skin and in a solid state produces an irreversible cornea opacity. Allergic effect was not found.

Acute Disease↗
PubMed1978

[Acute toxicity of l-naphthyl chlorocarbonate and o-isopropoxynitrobenzene].

The investigated compounds given orally to male rats induced pathological changes mainly in the liver. 1-naphthyl chlorocarbonate caused also necrosis of the stomach mucosa. DL50 of o-isopropoxynitrobenzene and 1-naphthyl chlorocarbonate established for male rats after per os administration amounted to 2,75 g/kg and 2,55 g/kg, respectively. Both substances have local irritant effect on the skin and the eye of rabbit--a mild reaction in case of o-isopropoxynitrobenzene and strong one in case of 1-naphthyl chlorocarbonate administration. 1-naphthyl chlorocarbonate has sensitizing properties, while the other compound has not.

Animals↗
PubMed1975

Stimulatory effects of chlordiazepoxide, diazepam and oxazepam on the drug-metabolizing enzymes in microsomes.

5 days' exposure of rats to daily doses of 400 mg/kg body wt. of chlordiazepoxide, diazepam and oxazepam stimulated the microsomal metabolism in the liver, as evidenced by acceleration of both p-hydroxylation of aniline and hydroxylation of benzene. The effect was accompanied by an increased concentration of liver microsomal protein and by the development of tolerance to the drugs. Similar effects were found after exposure of rats to lower doses of the drugs. The metabolism of aniline in vivo in rats treated with chlordiazepoxide was accelerated; this was correlated with development of tolerance to these drugs. It is suggested that both the stimulation of microsomal metabolism and the development of tolerance are associated with the induction of microsomal drug-metabolizing enzymes.

Aniline Compounds↗