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W Gärtner

Publications and source records attributed to W Gärtner.

51 records · Page 3Linked to original sources
PubMed1994

Photoinduced volume changes associated with the early transformations of bacteriorhodopsin: a laser-induced optoacoustic spectroscopy study.

Volume changes associated with the primary photochemistry of bacteriorhodopsin (BR) were measured by temperature-dependent laser-induced optoacoustic spectroscopy (LIOAS). Excitation was performed with 8-ns flashes establishing a photoequilibrium between the BR and the K states (BR<-->hvK). The concentration of K at the end of the laser pulse, which is an important parameter for the calculation of the volume change per molecule from the LIOAS data, was determined by flash photolysis with optical detection under the specific conditions (concentration, photon density) of the LIOAS experiment. Temperature-dependent measurements yielded a linear dependency of the ratio of the optoacoustic signals for BR and for a calorimetric reference (CoCl2) with the cubic thermal expansion coefficient beta of water. From the slope of this linear ratio a contraction of 11 cm3/mol was determined.

Bacteriorhodopsins↗
PubMed1991

Quantum yield of CHAPSO-solubilized rhodopsin and 3-hydroxy retinal containing bovine opsin.

The quantum yields of bleaching for two artificial pigments, bovine opsin combined with (3R)-3-hydroxy retinal or (3R,S)-3-methoxy retinal, were determined in comparison to the value for regenerated bovine rhodopsin. Regeneration of the visual pigments was performed by incubation of 3-[(3-Cholamidopropyl)-dimethylammonio]-2-hydroxy-1- propanesulfonate (CHAPSO)-solubilized opsin with the 11-cis isomers of retinal and the respective retinal derivatives. The extinction coefficients of the pigments in CHAPSO were determined to 35,000 M-1 cm-1 (native rhodopsin), 35,300 M-1 cm-1 (regenerated rhodopsin) and 34,500 M-1 cm-1 (3-OH retinal opsin). With respect to rhodopsin (lambda max: 500 nm), the pigments carrying the substituted chromophores exhibit blue shifted absorbance maxima (3-hydroxy and 3-methoxy retinal opsin: 488 nm). In parallel experiments under absolutely identical conditions we find related to the value of CHAPSO solubilized rhodopsin (identical to 1) a quantum efficiency of bleaching for the 3-hydroxy pigment of 1.2.

Animals↗
PubMed1990

Determination of the active metabolite of molsidomine in human plasma by reversed-phase high-performance liquid chromatography.

A reversed-phase high-performance liquid chromatographic method, with ultraviolet detection, is proposed for the plasma determination of SIN-1, the active metabolite of molsidomine, which involves propoxycarbonyl derivatization. The internal standard is the ethoxycarbonyl derivative of SIN-1 (i.e. molsidomine). Derivatization and extraction are each performed in one step (2 min) with 70% yield. The nature of a by-product is discussed. The method provides rapid elution (less than 15 min), linearity over the range 0.4-200 ng/ml, day-to-day precision between 2.5 and 11.3% and a limit of determination of 0.5 ng/ml. This method is also suitable for the simultaneous determination of molsidomine and SIN-1. In this case the internal standard is an ethoxycarbonyl derivative of a piperazino-3-sydnonimine, a SIN-1 analogue.

Antihypertensive Agents↗
PubMed1990

The photoreaction of active-site-methylated bacteriorhodopsin: an investigation using static and time-resolved infrared difference spectroscopy.

The photoreaction of active-site-methylated, permethylated bacteriorhodopsin has been investigated by static and time-resolved UV-vis and infrared difference spectroscopy. Additional information on the isomeric composition of the initial state and of photoproducts was obtained by retinal extraction and subsequent HPLC analysis. The data show that the dark-adapted state contains only all-trans-retinal. Prolonged illumination produces a metastable state which contains essentially only 9-cis-retinal and which decays back to the dark-adapted initial state within 8 h. The time-resolved infrared difference spectra clearly demonstrate that laser flash excitation produces an intermediate that has all the characteristics of the L intermediate. It is demonstrated that the methyl group at the Schiff base nitrogen introduces a steric hindrance with the protein which inhibits a photoreaction at 80 K, but which allows the generation of an L-like intermediate at room temperature and 173 K.

Bacteriorhodopsins↗
PubMed1988

Methoxyretinals in bacteriorhodopsin. Absorption maxima, cis-trans isomerization and retinal protein interaction.

Analogue bacteriorhodopsins (BRs) were reconstituted from bacterioopsin and 9-, 11-, or 13-methoxyretinals or their demethyl derivatives, respectively. In organic solvents the retinals occur as cis isomers of the respective double bonds carrying the methoxy group. 9-Methoxyretinal, present as the 9-cis isomer, does not form an analogue BR with bacterioopsin in the dark. Upon illumination, a BR is produced with an absorbance maximum at 560 nm. This compound is thermally unstable, and converts back into the 9-cis-containing complex (lambda max = 410 nm) in the dark. Removal of the 13-methyl group from this compound (= 9-methoxy 13-demethyl retinal) does not change the 9-cis configuration of the free retinal, but allows the reconstitution of a thermally stable chromoprotein absorbing around 500 nm with a proton translocation rate of about 10% of the BR value, comparable to the 13-demethyl BR value [Gärtner, W., Towner, P., Hopf, H. & Oesterhelt, D. (1983) Biochemistry 22, 2637-2644]. 11-Methoxy BRs (13-demethyl and 9,13-didemethyl) absorb around 530 nm and are inactive. 13-Methoxy retinal (13-cis isomer) reconstitutes a chromoprotein with an absorbance maximum at 515 nm, which can be photoconverted to a thermostable 460-nm-absorbing complex. For the 515-nm-absorbing species of 13-methoxy BR a light-induced proton translocation was not detected in measurements with cell vesicles (detection of pH changes in the vesicle preparation). Only by photocurrent measurements in a bilayer experiment could a very diminished photocurrent be detected, about 1-2% of BR, [Fendler et al. (1987) Biochim. Biophys. Acta 893, 60-68]. The reconstitution rate of 13-methoxy BR from 13-methoxy retinal and bacterioopsin is slower by a factor of 40 compared to 13-ethyl BR, although both substituents are of similar size. The position 13 of retinal was found to be most sensitive for regulation of the absorption maximum and the formation and stability of the all-trans isomer, which is the active form for light-induced proton translocation. The results suggest that an electronic interaction with a charged residue of the binding site exists around position 13 of retinal, which is disturbed when a methoxy group replaces the methyl or ethyl group at that position. This electronic interaction is essential for maintaining the active all-trans configuration of retinal.

Bacteriorhodopsins↗
PubMed1988

Rhodopsin-lumirhodopsin phototransition of bovine rhodopsin investigated by Fourier transform infrared difference spectroscopy.

The rhodopsin-lumirhodopsin transition has been investigated by Fourier transform infrared difference spectroscopy using isotope-labeled retinals. In the transition, two protonated carboxyl groups are involved. Another carbonyl band, located at 1725 cm-1 in rhodopsin, is shifted to 1731.5 cm-1 in lumirhodopsin. This line is tentatively assigned to a carbonyl stretching vibration of a peptide bond adjacent to the nitrogen of a proline residue. The C=N stretching vibration of rhodopsin could unequivocally be assigned to a band at 1659 cm-1. In contrast to rhodopsin and bathorhodopsin, the C=N stretching vibration of lumirhodopsin is at a low position, i.e., at 1635 cm-1, and exhibits only a downshift of 4 cm-1 upon deuteriation of the nitrogen. The C15-H rocking vibration of rhodopsin is assigned to the unusual high position of 1456 cm-1 and shifts into the normal region upon formation of lumirhodopsin. From these results, it is concluded that, whereas the environment of the Schiff base in rhodopsin, bathorhodopsin, and isorhodopsin is approximately the same, large changes occur with the formation of lumirhodopsin. From the assignment of the C10-C11 stretching vibration in bathorhodopsin and lumirhodopsin, a 10-s-cis geometry of lumirhodopsin can be excluded.

Animals↗
PubMed1987

The secondary structure of bacteriorhodopsin determined by Raman and circular dichroism spectroscopy.

The secondary structure of bacterio-opsin (BO), the retinal free protein-component of bacteriorhodopsin (BR), has been determined by Raman spectroscopy. Additional circular dichroism (CD) measurements have revealed only negligible conformational differences between BO in apomembranes and BR in purple membranes. Therefore, the secondary structure of BR was derived from the Raman data of BO. The protein conformation was determined to consist of 72-82% helices, 2-11% beta-strands, and 11-17% beta-turns. Only about half of the helical structures correspond to alpha 1-helices, the other half possess non-alpha 1-helical structures. According to the analysis of the Raman data, the derived secondary structure of BR was obtained with high reliability for all structure classes which can be distinguished by this method within the given uncertainty range. This is a remarkable difference from recently published secondary structural data derived from CD measurements where the helix content was reported to be between 50 and 80%. The inherent experimental and methodological uncertainties of the CD-technique leading to such a range of variation are critically discussed in comparison to the method of Raman spectroscopy. The combined application of Raman and CD spectroscopy, as performed here, is demonstrated to be a substantial improvement in the secondary structure determination of retinal-containing membrane proteins. On the basis of our results, some of the recently proposed structural models of BR with a beta-strand content of more than 11% can be ruled out.

Bacteriorhodopsins↗
PubMed1986

Liver function and pharmacokinetics of molsidomine and its metabolite 3-morpholinosydnonimine in healthy volunteers.

Plasma levels of N-carboxy-3-morpholinosydnonimine ethyl ester (molsidomine, Corvaton) and its pharmacologically active metabolite 3-morpholinosydnonimine (SIN-1) were measured in six healthy male and female volunteers after single intravenous and oral dosing of 4 mg molsidomine. Additionally indocyanine green and phenazone (antipyrine) clearances were determined to estimate hepatic blood flow and metabolic liver function in each subject. The pharmacokinetic parameters of molsidomine were similar to already published data in healthy volunteers and patients. The plasma level of SIN-1 formed was always lower than the molsidomine level but obviously reflects the corresponding molsidomine concentration time course in plasma. Indocyanine green plasma clearance was reduced by 15%. after intravenous dosing of 4 mg molsidomine. There was no clear-cut relationship between the plasma clearances of molsidomine and phenazone in these subjects with normal metabolic liver function.

Adult↗
PubMed1985

Relationship between pharmacokinetics and pharmacodynamics of molsidomine and its metabolites in humans.

The pharmacokinetic properties and hemodynamic effect of molsidomine and its pharmacologically active metabolite SIN-1 were investigated in 13 healthy volunteers following single oral doses. Hemodynamic changes were measured by finger plethysmography (peripheral arterial resistance), impedance plethysmography (venous distensibility), heart rate, and blood pressure. Plasma concentrations of molsidomine, SIN-1, and SIN-1C were measured by means of high-pressure liquid chromatography. Oral administration of rapidly dissolving tablets of molsidomine (2 tablets of 4 mg), a sustained-release form of molsidomine (8 mg), and SIN-1 (4 mg) caused an increase of the a/b ratio of the finger plethysmogram and an increase of the venous distensibility. Heart rate and blood pressure remained unaffected. The time course of the peripheral arterial effect mimicked the time course of plasma concentrations of molsidomine and SIN-1. Similar to the results in animals, molsidomine was metabolized in humans to SIN-1 and subsequently degraded to the inactive metabolite SIN-1C. The kinetic profile of both metabolites could be followed in the plasma. The rate-limiting step in the metabolic sequence of molsidomine was found to be enzymatic hydrolysis and decarboxylation of molsidomine to SIN-1. Concentration-response curves of the a/b ratio of the finger plethysmogram showed that the plasma concentrations required to produce a definite effect are much higher for molsidomine than for SIN-1. This shows that the pharmacodynamically active form of molsidomine in humans is the metabolite SIN-1. The changes in the finger plethysmogram produced by SIN-1 suggest that in addition to the effect on the venous site, SIN-1 also dilates the peripheral arterial site.

Adult↗
PubMed1984

Determination of pirlindole in plasma and urine by high-performance liquid chromatography.

A high-performance liquid chromatographic method is described for the analysis of pirlindole [2,3,3a,4,5,6-hexahydro-8-methyl-1H-pyrazino(3,2,1-jk)carbazole hydrochloride], a new antidepressive drug. The drug was extracted from plasma into dichloromethane, and the analysis was carried out on a reversed-phase column, the effluent being monitored by fluorescence detection. The method is selective and sensitive (limit of detection 1-2 ng/ml plasma). Urine analysis was done by direct injection of the diluted sample. The method was applied to the analysis of plasma and urine samples of eight healthy male volunteers who received a 75-mg oral dose of a tablet formulation of pirlindole. The method was also applied to a study in three beagle dogs which received pirlindole (1 mg/kg) by infusion (0.1 mg/kg/min) and orally (10 mg/kg) to estimate the absolute bioavailability of the drug.

Animals↗