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G Lassmann

Publications and source records attributed to G Lassmann.

At least 19 recordsLinked to original sources
PubMed1992

Spectral analysis of the protein-derived tyrosyl radicals from prostaglandin H synthase.

We have analyzed the low temperature EPR spectra of the protein-derived tyrosyl radicals detected upon addition of arachidonic acid or 5-phenyl-4-pentenyl-1-hydroperoxide (PPHP) to prostaglandin H synthase. With either arachidonic acid or PPHP the initial radical detected is a doublet (peak-to-trough = 35 Gauss) that disappears rapidly and is replaced by a broad singlet (peak-to-trough = 30 Gauss) followed by a narrow singlet (peak-to-trough = 26.5 Gauss). The relative amounts of these signals vary with time and concentration of arachidonic acid. The three tyrosyl radical signals were subjected to computer simulation and power saturation analysis. The data establish that there are only two distinct tyrosyl radical species, the doublet and the narrow singlet. The broad singlet seen at intermediate times and at low arachidonic acid concentrations is a composite of the doublet and the narrow singlet. The composition of the broad singlet in incubations of prostaglandin H synthase with 0.5 mM arachidonic acid is approximately 40% doublet and 60% singlet. The broad singlet signal does not represent a distinct tyrosyl radical species.

Alkenes↗
PubMed1992

EPR stopped-flow studies of the reaction of the tyrosyl radical of protein R2 from ribonucleotide reductase with hydroxyurea.

The reaction of the functional tyrosyl radical in protein R2 of ribonucleotide reductase from E. coli and mouse with the enzyme inhibitor hydroxyurea has been studied by EPR stopped-flow techniques at room temperature. The rate of disappearance of the tyrosyl radical in E. coli protein R2 is k2 = 0.43 M-1 s-1 at 25 degrees C. The reaction follows pseudo-first-order kinetics up to 450 mM hydroxyurea indicating that no saturation by hydroxyurea takes place even at this high concentration. Transient nitroxide-like radicals from hydroxyurea have been detected for the first time in the reaction of hydroxyurea with protein R2 from E. coli and mouse, indicating that 1-electron transfer from hydroxyurea to the tyrosyl radical is the dominating mechanism in the inhibitor reaction. The hydroxyurea radicals appear in low steady-state concentrations during 2-3 half-decay times of the tyrosyl radical and disappear thereafter.

Animals↗
PubMed1991

Electron spin resonance investigation of tyrosyl radicals of prostaglandin H synthase. Relation to enzyme catalysis.

We have examined, by low temperature ESR, the protein-derived radicals formed by reaction of purified ram seminal vesicle prostaglandin H synthase (PHS). Upon addition of arachidonic acid or 5-phenyl-4-pentenyl-1-hydroperoxide (PPHP) to PHS reconstituted with Fe(III)-protoporphyrin IX (Fe-PHS) at -12 degrees C, an ESR spectrum was observed at -196 degrees C containing a doublet that rapidly converted into a singlet. These protein-derived radicals were identified as tyrosyl radicals. The addition of a peroxidase substrate, phenol, completely abolished the appearance of the doublet and suppressed the formation of the singlet but did not inhibit eicosanoid formation. Incubation of arachidonic acid with PHS reconstituted with Mn(III)-protoporphyrin IX (Mn-PHS) produced only a broad singlet that exhibited different power saturation behavior than the tyrosyl radicals and decayed more rapidly. This broad singlet does not appear to be a tyrosyl radical. No ESR signals were observed on incubation of PPHP with Mn-PHS, which has cyclooxygenase but not peroxidase activity. Eicosanoid synthesis occurred very rapidly after addition of arachidonic acid and was complete within 1 min. In contrast, the protein-derived radicals appeared at a slower rate and after the addition of the substrate reached maximal levels between 1 and 2 min for Fe-PHS and 4-6 min for Mn-PHS. These results suggest that the observed protein-derived radicals are not catalytically competent intermediates in cyclooxygenase catalysis by either Fe-PHS or Mn-PHS. The peroxidase activity appears to play a major role in the formation of the tyrosyl radicals with Fe-PHS.

Alkenes↗
PubMed1990

Quenching of tyrosine radicals of M2 subunit from ribonucleotide reductase in tumor cells by different antitumor agents: an EPR study.

The inhibition of ribonucleotide reductase (RR) of intact Ehrlich ascites tumor cells by different antitumor agents was compared using EPR spectroscopy. The inactivation of M2 subunit was measured via quenching of the functionally essential tyrosine radical. Inhibitors of different classes, for example, hydroxyurea, pyrogallol, and thiosemicarbazones, differ in their efficiency by three orders of magnitude. Most effective inhibition was found for isoquinoline-1-aldehyde-thiosemicarbazone (IQ-1) with an IC50 value of 0.18 microM. Inhibition of RR inside tumor cells is comparable with that reported for isolated enzymes.

Animals↗
PubMed1989

Transient functional obstruction of the colon in neonates: examination of its development by manometry and biopsies.

Between 1975 and 1983, 17 neonates with transient functional obstruction of the colon were studied in our surgical department. Five could be successfully treated conservatively with enemas. In the remaining 12 cases colostomy was necessary. In three cases colostomy was performed too late and the patients died. In the other nine cases rectal biopsies and anorectal manometries were performed repeatedly. In spite of clear radiological signs of colonic obstruction such as in Hirschsprung's disease in each case, and identical clinical signs, true aganglionosis could be excluded. Rectoanal manometry 4 months after colostomy showed that the situation had normalized in five cases, but was still pathological in four cases, as in aganglionosis. Of the rectal biopsies, five showed signs of immaturity of ganglionic cells and three were normal. Rectoanal manometry 12-24 months later showed normal reaction in all cases, and of the five cases with immaturity of the ganglionic cells at 4 months one was still pathologic at 12-24 months. In eight of 12 cases the colostomy was closed without relapse of the obstruction, even on long-term follow up. Aganglionosis of the ultrashort type was excluded. In cases of severe transient functional obstruction of the colon in neonates, in which colostomy is necessary, rectoanal manometry and rectal biopsies should be performed as early as possible. Rectoanal manometry, at least, should be done before closure of the colostomy to avoid relapse of the obstruction from closing it to early: the functional disturbance may persist for several months. The term "small left colon syndrome" should be abandoned in favor of "transient functional obstruction,", as the latter describes the clinical condition far better.

Biopsy↗
PubMed1989

Protection of melanoma cells against superoxide radicals by melanins.

Human melanoma cells transplanted into immunocompetent mice by the 6-day subrenal capsule technique are characterized by high resistance against immunological attack. This resistance is suggested to be the consequence of scavenging of superoxide free radicals by melanin. Scavenging of superoxide radicals by the melanoma cells was clearly demonstrated using electron spin resonance techniques. From comparison with synthetic melanins it is concluded that the scavenger effect can be attributed mainly to low-molecular-mass melanins synthesized in the melanoma cells whereas high-molecular-mass melanins are practically ineffective.

Animals↗
PubMed1989

ESR studies of structure and kinetics of radicals from hydroxyurea. An antitumor drug directed against ribonucleotide reductase.

Hydroxyurea (HU) is a clinically applied antineoplastic drug, which quenches tyrosine radicals in the active site of ribonucleotide reductase (RR) and inhibits DNA synthesis in proliferating cells. Under oxidizing conditions (Cu2+ or H2O2) long-lived radicals from HU have been found by ESR. The structure of HU radicals was established to be: (formula; see text). The kinetics of formation and decay of HU radicals after reaction of HU with H2O2 is complex; it exhibits a lag-phase, a maximum, and a decay, all depending on the concentration of HU. Biological consequences of HU radicals for the inhibition of RR as well as their role in cytotoxic events during chemotherapy of cancer are discussed.

Antineoplastic Agents↗
PubMed1989

Stability and reactivation of tyrosine radicals from ribonucleotide reductase in tumor cells studied by ESR.

Naturally occurring tyrosine radicals from the M2 subunit of ribonucleotide reductase (RR) have been recorded by ESR in proliferating ordinary Ehrlich-ascites (EA) tumor cells of mice. Tyrosine radicals are stable in EA cells at room temperature for 2 h. Up to 500 mW no microwave saturation occurs. The relatively high stability and non-saturation of tyrosine radicals in EA cells suggests a suitable protein conformation in the M2 subunit enabling a close contact between the tyrosine radical and the antiferromagnetic iron complex. This facilitates an ESR study of functionally essential tyrosine radicals of RR in EA cells at low temperature and recommends this cellular system for studying such processes as inhibition and activation, which change the content of tyrosine radicals of the proliferation-linked RR. Oxygen treatment of non-proliferating (quiescent) EA cells reactivates tyrosine radicals 2-3 fold as found in strongly proliferating cells. We conclude that in quiescent cells, suffering from a lack of oxygen due to their high density in the peritoneal cavity, a reactivation of tyrosine radicals occurs by oxidation of non-radical tyrosine residues of inactive M2 subunits.

Animals↗
PubMed1979

Tactile corpuscle-like structures in a case of plexiform neurofibromatosis.

Tactile corpuscle-like structures were identified in a plexiform neurofibroma, which was localized on the right cranial hemisphere os a 16-year-old boy and had necessitated repeated surgery. These structures were studied by light and electron microscopy. The origin of their component cells is, however, still controversial. We believe to have accumulated sufficient evidence for a Schwann cell origin of these cells.

Adolescent↗
PubMed1979

Stereochemical properties of the binding site of liver microsomal cytochrome P-450 as studied by substrate analogous spin labels.

For the characterization of the substrate binding site optical and EPR measurements with spin labelled substrates on solubilized and pure cytochrome P-450 were performed. Analogously to the unlabelled derivatives spin labelled n-alkylamines and isocyanides with different chain lengths are type II substrates. The Ks-values evaluated from optical (P-450 = 1.98 . 10(-6) M) and ESR (P-450 = 1.98 . 10(-4) M) measurements are very similar indicating no concentration dependences. Contrary to the unlabelled n-alkylamines the spin labelled compounds show an affinity almost independent of the chain lengths. The SL-substrates with a short distance between the functional group and the NO-group bound to P-450 induce pronounced changes of the ligand field of the heme iron and a large broadening of the signal of the immobilized nitroxide indicating intensive interactions between the unpaired electron of the nitroxide group and the paramagnetic heme iron. Elongation of the alkyl chains results in spectra of the Fe3+ complexes with only slight modification and a remained unbroadened signal of the immobilized nitroxide. The binding of the substrate through their functional groups together with a 1:1 stoichiometry of the P-450 SL-IC-complex give evidence for the same binding site in the near vicinity of the heme iron.

Animals↗
PubMed1977

[The neural periphery in lichen planus lesions (author's transl)].

In 12 patients suffering from generalized Lichen planus (L.p.) the neural periphery of lesions was studied by modern histochemical and electron microscopical methods. In contrast to the investigations published until now on this subject no signs of neural hyperplasia in L.p. could be found. Only some nerves localized in the Lichen planus infiltrate exhibited morphological changes indicating increased neural de- and regeneration in this region. According to the results obtained the nerve changes in L.p. are caused by the typical inflammatory reaction found in this dermatosis. Therefore the neural theory of L.p. cannot be sustained on a histological basis.

Adolescent↗
PubMed1977

Different types of benign nerve sheath tumors. Light microscopy, electron microscopy and autoradiography.

In a light-, electronmicroscopic and autoradiographic study different types of nerve sheath tumors were classified. Their cellular population was quantitatively evaluated in the electron microscope. In the neurinoma the predominant cell was found to be the Schwann cell, but in the different types of neurofibromata a variable content of connective tissue cells was noted. T-HE DIFFUSE NEUROFIBROMATA SHOWED A QUANTITATIVE CELLULAR COMPOSITION SIMILAR TO NORMAL PERIPHERAL NERVES. In the plexiform neurofibroma a large number of fibroblasts were present and in the argyrophilic neurofibroma high content of perineurial cells was found. In autoradiographic sections the tumors showed in general a low proliferation rate (L.i. 1-3.6%). In the argyrophilic neurofibrom a higher labelling index (9.5%) was found.

Adolescent↗
PubMed1977

[Clinical, histological and electron microscopic findings in neurofibromatosis (Recklinghausen's disease) occurring in childhood (author's transl)].

A follow-up study was carried out of the clinical symptoms and the radiological and histological alterations in five cases of neurofibromatosis (Recklinghausen's disease) with onset during early childhood. The clinical manifestation of the disease was predominantly restricted to the face. In the histological ultrastructural investigation different types of neurofibroma were detected (plexiform neurofibroma, argyrophilic neurofibroma and diffuse neurofibrma). Preliminary results are presented on the basis of a correlation between the clinical findings and the histological types of neurofibroma with special reference to the demarcation of the tumours, recurrence following surgical removal and the prognosis as to the clinical course of the disease. Nevertheless, definite conclusions will be possible only by continuous observation of a larger number of patients by means of standardized clinical, radiological and histological methods of investigation.

Adolescent↗
PubMed1976

Diminished content of enterochromaffin cells in the rectal mucosa of an infant.

This report deals with an extremely small number of enterochromaffin cells in the rectum of a newborn male. This finding occurred only in 200 biopsies. The correlations to connatal disturbances of the motility of the intestine in the newborn are discussed. The frequency of this alterations seems to be comparable with other disturbances of cells of the neural crest, as for example pigment anomalies. Although further biochemical investigations could not be carried out because of technical difficulties, the case seems to be worth publishing for theoretical and practical reasons and in view of the possibility of special treatment.

Chromaffin System↗
PubMed1976

Morton's metatarsalgia. Light and electron microscopic observations and their relation to entrapment neuropathies.

The dissected plantar nerves of 105 patients with clinical symptoms of Morton's disease were examined under light and electron microscopy. Of the 105 cases, 75 showed characteristic neuronal lesions; in the others different pathologic substrates responsible for the clinical symptoms could be demonstrated. The nervous lesions are characterized by: 1. Thickening of the walls of the endoneurial vessels produced by multiple layers of basement membranes. 2. Edema and sclerosis of the endoneurium. In the electron microscope the endoneurium was filled by deposits of fibrils with a tubular substructure and a diameter of 100-110 A. 3. Thickening of the perineurium. 4. Degeneration of the nerve fibers without signs of wallerian degeneration or obvious reactive Schwann's cell hyperplasia. The possible pathogenetic mechanisms of Morton's disease and some clinical problems are discussed.

Adult↗
PubMed1976

[Spectroscopic investigatons on the structural thermal stability of leucine aminopeptidase. ESR, CD and fluorescence studies].

The thermal behaviour of leucine aminopeptidase (LAP, EC: 3.4.11.1) from bovine eye lens has been investigated in the temperature region 20--70 degrees C by spin-labelling of SH-groups (ESR), by CD and by fluorescence of tryptophane residues. Enzymatic activity of LAP was compared with spectroscopic data in this temperature region. From 20-60 degrees C the structural parts (alpha, beta, random coil) estimated from CD spectra remain unchanged. Within 20-55 degrees C no irreversible exposure of tryptophane residues takes place. In both types of spin-labelled LAP the strong immobilizing environment of the label retains its highly ordered structure up to 55 degrees C. Reversible changes of mobility and polarity of the environment of the label induced by temperature within 20-50 degrees C do not reduce the enzymatic activity and are regarded as local loosening of ordered structure. At 65 degrees C strong precipitation occurs. From 55 degrees C to 65 degrees C tryptophane residues are irreversibly exposed. The highly ordered environment of the label is destroyed about 55 degrees C, and a considerable amount of spin label molecules is reduced at the NO group by exposed SH groups. The above mentioned local loosening of structure becomes irreversible at 60 degrees C. The environment of both labels dominating above 60 degrees C is highly mobile and strongly polar and represents an extensively unfolded conformation. Until 60 degrees C no essential disordering of protein structure leading to a decrease of enzymatic activity occurs. Above 60 degrees C a sharp breakdown of ordered structures takes place, which is accompanied by a strong diminution of enzymatic activity.

Animals↗