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Biomedical subjects

B Mayer

Publications and source records attributed to B Mayer.

At least 307 records · Page 17Linked to original sources
PubMed1992

Stimulation of human nitric oxide synthase by tetrahydrobiopterin and selective binding of the cofactor.

To check the stimulatory potency of the tetrahydro forms of the two major pteridines occurring in human tissues, neopterin and biopterin, NO synthase was purified 6000-fold from human cerebellum. Tetrahydrobiopterin stimulated the activity up to 4.5-fold in a concentration dependent manner with a maximum above 1 microM, whereas tetrahydroneopterin was completely inactive in concentrations up to 100 microM. Tetrahydrobiopterin, but not neopterin derivatives, were copurified with the NO synthase activity. Our results demonstrate that human cerebellum contains a tetrahydrobiopterin dependent NO synthase activity.

Amino Acid Oxidoreductases↗
PubMed1992

Ca2+/calmodulin-dependent cytochrome c reductase activity of brain nitric oxide synthase.

Nitric oxide acts as a widespread signal molecule and represents the endogenous activator of soluble guanylyl cyclase. In endothelial cells and brain tissue, NO is enzymatically formed from L-arginine by Ca2+/calmodulin-regulated NO synthases which require NADPH, tetrahydrobiopterin, and molecular oxygen as cofactors. Here we show that purified brain NO synthase binds to cytochrome c-agarose and exhibits superoxide dismutase-insensitive cytochrome c reductase activity with a Vmax of 10.2 mumol x mg-1 x min-1 and a Km of 34.1 microM. Cytochrome c reduction was largely dependent on Ca2+/calmodulin and cochromatographed with L-citrulline formation during gel filtration. When reconstituted with cytochrome P450, NO synthase induced a moderate Ca(2+)-independent hydroxylation of N-ethylmorphine. NO synthase also reduced the artificial electron acceptors nitro blue tetrazolium and 2,6-dichlorophenolindophenol. Cytochrome c, 2,6-dichlorophenolindophenol, and nitro blue tetrazolium inhibited NO synthase activity determined as formation of L-citrulline from 0.1 mM L-arginine in a concentration-dependent manner with half-maximal effects at 166, 41, and 7.3 microM, respectively. These results suggest that NO synthase may participate in cellular electron transfer processes and that a variety of electron-acceptors may interfere with NO formation due to the broad substrate specificity of the reductase domain of NO synthase.

2,6-Dichloroindophenol↗
PubMed1992

Ca2+/calmodulin-dependent formation of hydrogen peroxide by brain nitric oxide synthase.

L-Arginine-derived nitric oxide (NO) acts as an inter- and intra-cellular signal molecule in many mammalian tissues including brain, where it is formed by a flavin-containing Ca2+/calmodulin-requiring NO synthase with NADPH, tetrahydrobiopterin (H4biopterin) and molecular oxygen as cofactors. We found that purified brain NO synthase acted as a Ca2+/calmodulin-dependent NADPH:oxygen oxidoreductase, catalysing the formation of hydrogen peroxide at suboptimal concentrations of L-arginine or H4biopterin, which inhibited the hydrogen peroxide formation with half-maximal effects at 11 microM and 0.3 microM respectively. Half-maximal rates of L-citrulline formation were observed at closely similar concentrations of these compounds, indicating that the NO synthase-catalysed oxygen activation was coupled to the synthesis of L-citrulline and NO in the presence of L-arginine and H4biopterin. N omega-Nitro-L-arginine, its methyl ester and N omega-monomethyl-L-arginine inhibited the synthesis of L-citrulline from L-arginine (100 microM) with half-maximal effects at 0.74 microM, 2.8 microM and 15 microM respectively. The N omega-nitro compounds also blocked the substrate-independent generation of hydrogen peroxide, whereas N omega-monomethyl-L-arginine did not affect this reaction. According to these results, activation of brain NO synthase by Ca2+ at subphysiological levels of intracellular L-arginine or H4biopterin may result in the formation of reactive oxygen species instead of NO, and N omega-nitro-substituted L-arginine analogues represent useful tools to effectively block NO synthase-catalysed oxygen activation.

Amino Acid Oxidoreductases↗
PubMed1992

Tetrahydrobiopterin-dependent formation of endothelium-derived relaxing factor (nitric oxide) in aortic endothelial cells.

Inhibition of tetrahydrobiopterin (H4biopterin) biosynthesis in endothelial cells almost completely abolished the agonist-induced formation of endothelium-derived relaxing factor (EDRF) (NO). This inhibitory effect could be antagonized when H4biopterin biosynthesis was restored by activating a salvage pathway. These data indicate that the formation of EDRF strictly depends on the presence of intracellular H4biopterin, which, in addition to Ca2+, may represent a further physiological and/or pathophysiological regulatory of endothelial NO synthases.

Animals↗
PubMed1992

Characterization of soluble platelet guanylyl cyclase with peptide antibodies.

Soluble guanylyl cyclase partially purified from bovine and human platelets was characterized with antibodies raised against synthetic peptides corresponding to different sequences of the alpha 1- and beta 1-subunits of the bovine lung enzyme. On immunoblots, the platelet guanylyl cyclase was recognized by the four antisera used, with the exception of an antiserum against the C-terminus of the beta 1-subunit which did not react with the human platelet but with the bovine platelet beta 1-subunit. Furthermore the human platelet beta 1-subunit exhibited a slightly lower molecular mass than the bovine protein. The C-terminal antibodies precipitated native platelet and lung guanylyl cyclase activity. In contrast an antibody against a peptide out of the putative catalytic domain, which is highly conserved between all guanylyl cyclases sequenced so far, did not precipitate native guanylyl cyclase, although it recognized both subunits on immunoblots, suggesting that the respective amino acid sequence is located in an inner site of the protein.

Amino Acid Sequence↗
PubMed1992

Expression of nitric oxide synthase in kidney macula densa cells.

The distribution of nitric oxide synthase (NOS), the enzyme by which NO is generated from L-arginine, was investigated in rat kidney. The indirect immunofluorescence technique using a polyclonal antibody against type I NOS was applied, followed by the histochemical NADPH diaphorase staining technique on the same sections in order to demonstrate the enzymatic activity of NOS. Macula densa cells were strongly stained by both techniques, demonstrating abundant NOS in the cytoplasm of these cells. In addition, these findings were confirmed by nonradioactive in situ hybridization, thus demonstrating the corresponding messenger RNA in macula densa cells as well. Our findings provide the morphological basis for a possible role of NO as a mediator substance in signal transfer from distal tubular fluid to glomerular arterioles.

Amino Acid Oxidoreductases↗
PubMed1992

[Interposition connectors with heparin coating for vascular anastomosis of microsurgical tissue flaps].

The intraluminal surface of interposition connectos which are introduced for the quick vascular connection of microsurgical free flaps was coated by heparin. This heparin coating proved to be stable at the polyurethane wall until the intraluminal surface of the interposition connectors with a length of 15 mm was coated by a layer of endothelial cells. 90% of the experimental venous connections didn't show a thrombus formation and were open for the blood flow 10 days postoperatively. The experimental free flaps which were connected by this way had survived 21 days postoperatively and showed a regular healing.

Anastomosis, Surgical↗
PubMed1992

[Rhinoplasty: preventable errors in the first 100 interventions and secondary correction].

The most frequent avoidable mistakes which a young rhinosurgeon commits concern the analysis of the patient's desire, the preoperative critical examination of the facial proportions, the choice of the surgical technique and the operative approach, the choice of the implantation material and the method of how to implant it in a form-fitting manner, overreductions or underreductions by osteotomy and mistakes in the course of postoperative change of the dressings. The way of avoiding these errors and the way of their secondary correction are presented. The principle of a secondary operation is a structural reorientation by a few minor surgical steps.

Bandages↗
PubMed1992

Nitric oxide synthase in VIP-containing vasodilator nerve fibres in the guinea-pig.

We investigated the possibility of nitric oxide (NO), a powerful vasodilator agent, being synthesized by perivascular nerve fibres. Immunoreactivity and catalytic activity of the NO synthesizing enzyme, NO synthase (NOS), were demonstrated in perivascular nerve fibres of blood vessels receiving autonomic vasodilator innervation, but not of those innervated exclusively by vasoconstrictor nerve fibres. Double-labelling techniques allowed identification of NOS-containing nerve fibres as belonging to the vasoactive intestinal peptide (VIP)/acetylcholine-containing class whereas noradrenergic and substance P-containing perivascular fibres were devoid of NOS. We suggest that, in addition to its endothelial source, NO is a neuronal co-mediator of VIP/cholinergic vasodilation.

Amino Acid Oxidoreductases↗
PubMed1992

Nitric oxide synthase-catalyzed activation of oxygen and reduction of cytochromes: reaction mechanisms and possible physiological implications.

Purified cerebellar nitric oxide (NO) synthase was found to reduce molecular oxygen to hydrogen peroxide at low concentrations of its substrate L-arginine or its cofactor tetrahydrobiopterin. The characteristics of oxygen reduction appeared to be similar to NO synthesis, as both reactions required reduced nicotinamide adenine dinucleotide phosphate (NADPH), were dependent on Ca2+/calmodulin, and showed optimal reaction rates at slightly acidic conditions. The electron transport from NADPH to molecular oxygen is probably mediated by the reduced flavins, flavine adenine dinucleotide (FAD) and flavin mononucleotide (FMN), which are bound in stoichiometrical amounts to the enzyme. NO synthase shows similarities to cytochrome P450 (cytochrome c) reductase, another FAD- and FMN-containing enzyme, and we found that NO synthase reduced cytochromes and artificial, low molecular mass electron acceptors in a superoxide dismutase-insensitive manner. Thus, NO synthase apparently represents a Ca(2+)-regulated, soluble isoform of cytochrome P450 reductase.

Amino Acid Oxidoreductases↗
PubMed1992

Regulation of neuronal nitric oxide and cyclic GMP formation by Ca2+.

Nitric oxide (NO) acts as a messenger molecule in the CNS by activating soluble guanylyl cyclase. Rat brain synaptosomal NO synthase was stimulated by Ca2+ in a concentration-dependent manner with half-maximal effects observed at 0.3 microM and 0.2 microM when its activity was assayed as formation of NO and L-citrulline, respectively. Cyclic GMP formation was apparently inhibited, however, at Ca2+ concentrations required for the activation of NO synthase, indicating a down-regulation of the signal in NO-producing cells. Purified synaptosomal guanylyl cyclase was not inhibited directly by Ca2+, and the effect was not mediated by a protein binding to guanylyl cyclase at low or high Ca2+ concentrations. In cytosolic fractions, the breakdown of cyclic GMP, but not that of cyclic AMP, was highly stimulated by Ca2+, and 3-isobutyl-1-methylxanthine did not block this reaction effectively. The effects of Ca2+ on cyclic GMP hydrolysis and on apparent guanylyl cyclase activities were abolished almost completely in the presence of the calmodulin antagonist calmidazolium, whose effect was attenuated by added calmodulin. Thus, a Ca2+/calmodulin-dependent cyclic GMP phosphodiesterase is highly active in synaptic areas of the brain and may prevent elevations of intracellular cyclic GMP levels in activated, NO-producing neurons.

1-Methyl-3-isobutylxanthine↗
PubMed1992

Nitric oxide synthase in cardiac nerve fibers and neurons of rat and guinea pig heart.

Participation of nitric oxide (NO) in the autonomic innervation of rat and guinea pig hearts was investigated by applying the NADPH diaphorase technique and immunohistochemistry with NO synthase antiserum. We present evidence that NO synthase is localized in cardiac ganglion cells and nerve fibers innervating the sinuatrial and atrioventricular nodes, the myocardium, local neurons, coronary arteries, and pulmonary vessels, suggesting an involvement of NO in neurogenic heart rate regulation, myocardial cell function, neuronal transmission in cardiac ganglia, and coronary as well as pulmonary vasodilation.

Amino Acid Oxidoreductases↗
PubMed1992

[Duplex sonographic monitoring of infra-inguinal arterial reconstructions: can a threatened bypass occlusion be detected by this method?].

In our institution, 95 infrainguinal arterial reconstructions were prospectively entered into a graft surveillance programme which consisted of a postoperative i.a. DSA and routine assessment of graft flow velocity (GFV) and ankle pressure indices (ABI) during the first postoperative year. An average of 4.1 GFV measurements was obtained during a mean follow-up period of 8.2 months. Abnormal GFV led to arteriography in 29 bypasses identifying--aside from three false positive findings--two graft occlusions and 24 severe (> 70%) graft stenoses. Of the latter, in only 7 cases a significant decrease in ABI was found. Unheralded graft occlusion occurred in 6 patients. Including the corrections of the above mentioned lesions, secondary patency rates were 97% at 30 days and 89% at one year.

Aged↗
PubMed1992

[Determination of vascular resistance in bypass operations with infragenual anastomosis: is prediction of early occlusion possible with this value?].

Peripheral outflow resistance (OR) was assessed intraoperatively in 75 infrainguinal bypass procedures to the below knee popliteal artery (20) or a single crural artery (55). OR measurement was done after completion of the distal anastomosis. For that purpose, the graft was perfused with Ringer solution at constant flow rates of 100 and 150 ml/min using a roller pump. During infusion, arterial pressure was recorded. In this way distal (DOR) and total (TOR) outflow resistance in E/S anastomoses was calculated before and after vasodilatation with papaverine. DOR at a flow rate of 100 ml/min was found to be most discriminant as a predictor of early graft thrombosis: 1. In the limbs with a thrombosed graft at 30 days OR was significantly higher than in the limbs with a patent graft (1828 +/- 418 vs. 1472 +/- 221 mPRU; p less than 0.01, Mann-Whitney U-Test). 2. The cut-off value of 1700 mPRU, which was determined by ROC curves, was 100% sensitive and 81% specific in the group of femoro-crural grafts to predict early graft failure. A better discrimination by the application of papaverine could not be achieved. We concluded from our results that OR might be an important factor in early graft thrombosis. But still there is more experience required to select patients for primary amputation or adjunctive procedures (av-fistula, sequential graft) on the basis of the present available data.

Arterial Occlusive Diseases↗
PubMed1992

[The aging nose--considerations for rhinoplasty].

Typical features of the ageing nose require intense preoperative planning and a careful surgical technique. The motives for the operation vary: generally, the patients only wish for minimal changes to reduce the most obvious features. Basic technical details are presented.

Age Factors↗
PubMed1991

Brain nitric oxide synthase is a biopterin- and flavin-containing multi-functional oxido-reductase.

Brain nitric oxide synthase is a Ca2+/calmodulin-regulated enzyme which converts L-arginine into NO. Enzymatic activity of this enzyme essentially depends on NADPH and is stimulated by tetrahydrobiopterin (H4biopterin). We found that purified NO synthase contains enzyme-bound H4biopterin, explaining the enzymatic activity observed in the absence of added cofactor. Together with the finding that H4biopterin was effective at substoichiometrical concentrations, these results indicate that NO synthase essentially depends on H4biopterin as a cofactor which is recycled during enzymatic NO formation. We found that the purified enzyme also contains FAD, FMN and non-heme iron in equimolar amounts and exhibits striking activities, including a Ca2+/calmodulin-dependent NADPH oxidase activity, leading to the formation of hydrogen peroxide at suboptimal concentrations of L-arginine or H4biopterin.

Amino Acid Oxidoreductases↗