Biomedical subjects

M Wirtz

Publications and source records attributed to M Wirtz.

24 records · Page 2Linked to original sources

PubMed1999

An electrochemical study of the factors responsible for modulating the reduction potential of putidaredoxin.

The gene coding for putidaredoxin has been synthesized using a combination of chemical and enzymatic methods and subsequently expressed in Escherichia coli. The recombinant protein characterized by electronic spectroscopy, mass spectrometry, and electrochemistry was found to be identical to putidaredoxin obtained from Pseudomonas putida. Polylysine was found to promote the fast and reversible electrochemistry of putidaredoxin at negatively charged electrodes such as indium-doped tin oxide or gold surfaces modified with mercaptoalkanoate groups. The value of the heterogeneous electron transfer rate constant obtained from solutions containing a mixture of putidaredoxin and polylysine (k(s) = 1.3 x 10(-3) cm/s) is one order of magnitude larger than the values reported previously at gold electrodes modified with mercaptoethylamine or at antimony-doped tin oxide semiconductor electrodes. It was observed that when the reduction potential of putidaredoxin is measured by cyclic voltammetry, the resultant value is consistently more positive (64 mV) than the reduction potential measured with potentiometric titrations. A comparison between the electrochemical responses of putidaredoxin and spinach ferredoxin, combined with the examination of their corresponding three-dimensional structures, indicates that the positive shift in the reduction potential of putidaredoxin originates from the formation of a transient complex between putidaredoxin and polylysine at the electrode surface. The formation of this transient complex modulates the reduction potential of putidaredoxin by lowering the value of the dielectric constant around its iron-sulfur cluster microenvironment, specifically by neutralizing negative charges surrounding the active site and by excluding water from the solvent exposed iron sulfur cluster. The observed positive shift in E degrees ', which is induced by complexation with polylysine at the electrode-surface, suggests that similar factors are likely to contribute to the anodic shift in the E degrees ' of cytochrome P450(cam)-bound putidaredoxin (+44 mV) with respect to the E degrees ' measured for free putidaredoxin.

Amino Acid Sequence↗

PubMed1998

The reduction potential of cytochrome b5 is modulated by its exposed heme edge.

When the reduction potential of cytochrome b5 is measured with the aid of several different surface-modified electrodes that function on the basis of electrostatic interactions with the protein, the resultant values have been consistently more positive (40-100 mV) than the reduction potentials measured with potentiometric methods. In this paper, we report that the heme edge containing the exposed heme propionate, a heme methyl, and a heme vinyl, and which constitutes part of the surface of cytochrome b5, modulates its reduction potential. The positive shifts observed in the voltammetric measurements appear to originate from the formation of a complex between cytochrome b5 and the modified electrode surface which (a) neutralizes the charge on the heme propionate located on the exposed heme edge and (b) lowers the dielectric of the exposed heme microenvironment by excluding water from the complex interface, factors which result in the destabilization of the positive charge on the ferric heme with respect to the neutral ferrous heme. The observed positive shift, which is induced by complexation at the electrode surface, may indicate that similar shifts in the reduction potential of cytochrome b5 occur when it forms a complex with physiological partners, prior to electron transfer. The effect of the value of the dielectric constant on the reduction potential of cytochrome b5 was corroborated by preparing the V45L/V61L double mutant whose reduction potential was measured to be 50 mV more negative than the value measured for the wild type protein. The negative shift in the reduction potential of the mutant protein was explained by the increased accessibility of water to the heme binding site, as observed in its X-ray crystal structure.

Amino Acid Substitution↗

PubMed1998

Reproducibility of functional transcranial Doppler sonography in determining hemispheric language lateralization.

BACKGROUND AND PURPOSE: Since functional transcranial Doppler ultrasonography (fTCD) allows convenient and fully automated quantification of language lateralization, it seems ideal for longitudinal studies of perfusion changes during deterioration as well as recovery of language functions. However, during serial examinations, the technical, stochastic, and physiological variabilities of cerebral blood flow velocities (CBFV) have to be considered. Therefore, before fTCD is accepted as a tool for evaluation of changes in lateralization in the diseased state, its reliability in healthy subjects needs to be determined. METHODS: We performed fTCD during a word generation task based on a previously validated technique with automated calculation of the averaged CBFV differences in the middle cerebral arteries providing an index of lateralization (LI). RESULTS: (1) The accuracy of the LI as assessed by the confidence interval was better than 1% of the mean hemispheric difference. (2) On repeated examination, LIs obtained from 10 subjects showed a high test-retest reproducibility (Pearson product moment correlation coefficient r = 0.95, P < 0.0001). (3) On 10 repeated assessments of LI in the same subject, no practice effects were detected. CONCLUSIONS: Functional TCD is a suitable and very robust tool for the longitudinal quantitative measurement of cerebral language lateralization.

Adult↗

PubMed1991

[Lens epithelium necrosis factor for prevention lens opacity].

Posterior capsule opacification is a common postoperative complication after extracapsular cataract extraction and lens implantation. If the patient's visual acuity is reduced markedly, a capsulotomy with a Nd-YAG laser may become necessary. Various attempts have been made with the aim of developing an injectable solution capable of damaging the epithelial cells of the capsule bag irreversibly and thereby avoiding posterior capsule opacification. This solution should be applied for a short time during the operation. In tissue culture we tested the influence of two injectable solutions [lens epithelial necrosis factor (LENF)] and aqua bidest. on cellular growth. Balanced salt solution served as control. We used human epithelial carcinoma cells, type HEp-2. The results were evaluated by vital staining (ethidium bromide and acridin orange), hemotoxylin staining, autoradiography and measurement of protein and DNA synthesis. The results showed that LENF is capable of damaging 100% of the epithelial cells irreversibly if it is applied for 20 s or longer. The influence of each of these solutions was tested on 20 human capsular flaps, which were excised during the operation. The flaps were immersed for 30 s in the different solutions. Vital staining of these flaps led to the following results: LENF causes a 100% cell damage of all epithelial cells of the capsular flaps. No vital cells remained. On the other hand Aqua bidest. cannot guarantee 100% cell damage of the capsular flap epithelia. Sixty percent of the capsular flaps treated with aqua bidest, showed differing amounts of remaining vital cells.

Biological Factors↗

PubMed1987

[Therapy of latent cardiomyopathy with verapamil].

In an open, randomized cross-over trial lasting two months, 21 patients with latent cardiomyopathy were either untreated or received verapamil 120 mg three times daily. Angina and dyspnea improved in 14 of the 21 patients. These symptoms worsened in one, remained unchanged in six (P less than 0.05). During exercise the pulmonary artery diastolic pressure fell from a mean of 25.3 +/- 7.6 to 20.1 +/- 6.6 mm Hg (P less than 0.05); (at rest, from mean of 10.7 +/- 5.2 to 9.0 +/- 4.5 mm Hg - not significant). In nine patients with a raised resting PA diastolic pressure verapamil produced a significant reduction (from 15.4 +/- 2.7 to 11.1 +/- 4.1 mm Hg) (P less than 0.05). All other hemodynamic parameters remained unchanged. These clinically and hemodynamically favorable effects are possibly due to improved diastolic ventricular function by verapamil. In latent cardiomyopathy any impairment of diastolic relaxation may be more important pathogenetically than reduction in systolic ventricular function.

Adult↗

PubMed1987

Calcium antagonist treatment in mild forms of cardiomyopathy.

Twenty-one patients with a mild form of cardiomyopathy (with normal ejection fraction but histologically-confirmed hypertrophy of myocardial cells and/or elevated diastolic pulmonary artery pressure during exercise) received 120 mg verapamil t.i.d. or no therapy at all for a period of 2 months in an open randomized cross-over study. Out of the 21 patients, 14 improved clinically, one patient's condition deteriorated and six remained unchanged (p less than 0.05). The mean diastolic pulmonary artery pressure during exercise decreased (25.3 +/- 7.6 to 20.1 +/- 6.6 mm Hg, n = 21, p less than 0.05). At rest, the decrease was only significant in the subgroup with pressures above 12 mm Hg (15.4 +/- 2.7 to 11.1 +/- 4.1 mm Hg, n = 9, p less than 0.05). All other hemodynamic data displayed no significant change. The benefits of verapamil therapy may be attributed to an improvement in diastolic ventricular function. The disturbance in diastolic relaxation might be of greater importance than the disturbance in systolic function in patients with mild forms of cardiomyopathy.

Adult↗