Search PubMed⌕ Search

Biomedical subjects

H Zimmermann

Publications and source records attributed to H Zimmermann.

At least 19 recordsLinked to original sources
PubMed1992

Purification and characterization of a pore-forming protein from the marine sponge Tethya lyncurium.

A pore-forming protein was detected and purified for the first time from a marine sponge (Tethya lyncurium). The purified protein has a polypeptide molecular mass of 21 kDa and a pI of 6.4. Tethya pore-forming protein (also called Tethya hemolysin) rapidly lysed erythrocytes from a variety of organisms. After binding to target membranes, the hemolysin resisted elution with EDTA, salt or solutions of low ionic strength and hence resembled an integral membrane protein. Erythrocytes could be protected from hemolysis induced by Tethya hemolysin by addition of 30 mM dextran 4 (4-6 kDa; equivalent hydrodynamic diffusion radius, 1.75-2.3 nm) to the extracellular medium, but not by addition of uncharged molecules of smaller size [sucrose, raffinose and poly(ethylene glycol) 1550; equivalent hydrodynamic diffusion radii, 0.46, 0.57 and 1.2 nm, respectively]. This result indicates that hemolysin is able to form stable transmembrane pores with an effective diameter of about 2-3 nm. Treatment of osmotically protected erythrocytes with Tethya hemolysin caused a rapid efflux of intracellular K+ and ATP, and a rapid influx of extracellularly added Ca2+ and sucrose. In negative-staining electron microscopy, target erythrocyte membranes exposed to purified Tethya hemolysin displayed ultrastructural lesions but without visible pores.

Adenosine Triphosphate↗
PubMed1992

Soluble low-Km 5'-nucleotidase from electric-ray (Torpedo marmorata) electric organ and bovine cerebral cortex is derived from the glycosyl-phosphatidylinositol-anchored ectoenzyme by phospholipase C cleavage.

Soluble and membrane-bound low-Km 5'-nucleotidase was isolated from high-speed supernatants and membrane fractions derived from the electric organ of the electric ray (Torpedo marmorata) or from bovine brain cerebral cortex. Purification of both enzymes included chromatography on concanavalin A-Sepharose and AMP-Sepharose. The contribution to the total of soluble enzyme activity was lower in electric organ (1.6%) than in bovine cerebral cortex (27.9%). Membrane-bound and soluble forms have very similar Km values for AMP and are inhibited by micromolar concentrations of ATP. Both forms cross-react with, and are inhibited by, an antibody against the membrane-bound surface-located (ecto-) 5'-nucleotidase from electric organ. The HNK-1 carbohydrate epitope is present on both forms of the Torpedo enzyme, but is entirely absent from bovine cerebral-cortex 5'-nucleotidase. An antibody specific for the inositol 1,2-(cyclic)monophosphate that is formed on phospholipase C cleavage of an intact glycosyl-phosphatidylinositol (GPI) anchor binds to the soluble, but not to the membrane-bound, form of the enzyme from both sources. Our results suggest that soluble low-Km 5'-nucleotidase in both electric organ and bovine brain is derived from the membrane-bound GPI-anchored form of the enzyme by the action of a phospholipase C and is not a soluble cytoplasmic enzyme.

5'-Nucleotidase↗
PubMed1992

Reversibility of secondary biliary fibrosis by biliodigestive anastomosis in the rat.

Biliary cirrhosis with portal hypertension and hepatocellular failure is a well-known complication of extrahepatic obstruction. It is unclear to what extent these changes are reversible by biliodigestive anastomosis. Therefore a rat model of relief of biliary obstruction was developed by performing Roux-en-Y choledochojejunostomy in rats after bile duct obstruction. Patency of the biliodigestive anastomosis was documented by biliary scintigraphy. Microsomal function was assessed in vivo by the aminopyrine breath test and portal hypertension by spleen pulp pressure. Microsomal function was markedly impaired in obstructed animals but recovered after biliodigestive anastomosis. Microsomal cytochrome P450 content paralleled these changes. Similarly, portal hypertension was reversed after successful relief of obstruction. Stereologic analysis showed that biliodigestive anastomosis partially reversed bile ductular proliferation and fibrosis. Studying the time course of recovery showed that restoration of microsomal function was achieved after 2 weeks whereas recovery from portal hypertension required 4 weeks of biliary drainage. Recovery of microsomal function was paralleled by normalization of microsomal lipid composition while resolution of portal hypertension occurred parallel to resolution of the histologic abnormalities.

Anastomosis, Roux-en-Y↗
PubMed1992

In vitro binding of isolated synaptic vesicles to presynaptic plasma membranes: activation by Ca2+ and protein kinase C.

An in vitro model to study the molecular control of binding of highly purified synaptic vesicles to presynaptic plasma membranes has been developed. Presynaptic plasma membranes were immobilized by dotting onto nitrocellulose, and binding of iodinated synaptic vesicle membranes was studied under varying experimental conditions. Synaptic vesicles bind to presynaptic plasma membranes in the presence of Ca2+ and ATP. Binding is reduced in the presence of EGTA and abolished by the calmodulin antagonist trifluoperazine. Vesicle binding is stimulated 5-fold after incubation--prior to dotting--of presynaptic plasma membranes with ATP in the presence of the phorbol-ester 12-O-tetradecanoylphorbol-13-acetate (1 microM) and 2.5-fold after preincubation with Ca2+ (50 microM). Pretreatment of plasma membranes with alkaline phosphatase strongly reduces vesicle binding. Microsomes prepared from bovine liver did not bind to presynaptic plasma membranes. Our results suggest that activation of protein kinase C and Ca2+ stimulate binding of synaptic vesicles to the presynaptic membrane. In the intact nerve terminal this interaction may represent an initial step in synaptic vesicle exocytosis.

Alkaline Phosphatase↗
PubMed1992

Ursodeoxycholate has no beneficial effect on liver function or histology in biliary cirrhosis in the rat.

In different cholestatic conditions, the beneficial effects of the tertiary bile acid, ursodeoxycholate, have been described. It is unclear, however, whether ursodeoxycholate also affects the functional and structural alterations induced by chronic biliary obstruction. Therefore, we studied the effect of ursodeoxycholate (100 mg/kg/day) on microsomal function as assessed in vivo by the aminopyrine breath test, on portal hypertension and on the structural composition of the liver in rats with chronic (3-week) biliary obstruction. Hepatic composition was assessed stereologically. Ursodeoxycholate had no effect on any of the parameters measured. We conclude that this form of treatment does not affect advanced liver disease due to common bile duct obstruction. This finding supports one of the proposed mechanisms of action of ursodeoxycholate, namely that it interferes with the ileal absorption of more toxic endogenous bile salts.

Animals↗
PubMed1991

5'-nucleotidase from the electric ray electric lobe. Primary structure and relation to mammalian and procaryotic enzymes.

A cDNA encoding a 5'-nucleotidase was identified by screening a lambda gt10 cDNA library from the electric lobe of Discopyge ommata using a cDNA probe containing the complete open reading frame coding for the rat liver enzyme. Nucleotide sequence analysis defines an open reading frame of 577 amino acids, corresponding to a calculated molecular mass of 63,833 Da. The N-terminus of the mature protein, as determined by direct protein sequencing, is preceded by 29 amino acid residues comprising a signal peptide. The C-terminus contains a stretch of hydrophobic amino acids, considered to be cleaved on post-translational modification and exchanged for glycosylphosphatidylinositol as a membrane anchor. The predicted protein contains four potential N-linked glycosylation sites. Electric ray 5'-nucleotidase shares 61% amino acid identity with the enzymes from rat liver and human placenta, and about 23% with bacterial proteins possessing 5'-nucleotidase activity and also additional enzyme activities like UDP-glucose hydrolase. Polyclonal antibodies raised against 5'-nucleotidase from mammalian sources or the electric ray electric organ reveal mutual cross-reactivity. Interestingly, there are 5-7 domains highly conserved in procaryotes and vertebrates in enzymes exhibiting 5'-nucleotidase, 3'-nucleotidase or phosphodiesterase activity. 5'-nucleotidase isolated from Torpedo electric organ hydrolyzes UDP-glucose at 8% of the rate of AMP hydrolysis. The possible phylogenetic origin of vertebrate 5'-nucleotidase from multifunctional nucleotide hydrolases is discussed.

5'-Nucleotidase↗
PubMed1991

Association of the HNK-1 epitope with 5'-nucleotidase from Torpedo marmorata (electric ray) electric organ.

5'-Nucleotidase isolated from the electric organ of the electric ray (Torpedo marmorata) has a molecular mass of 62 kDa and, on two-dimensional electrophoresis, separates into up to 13 isoforms within a pI range of 5.9-6.7. The N-terminal sequence data show a 71% identity over 17 amino acids with that previously published for the rat liver enzyme. All forms of 5'-nucleotidase are recognized by the HNK-1 monoclonal antibody. HNK-1 immunoreactivity is found at the surface of the Schwann-cell processes covering the synaptic terminals and in this respect corresponds to that of 5'-nucleotidase in the same tissue. Since a number of glycoproteins involved in cell recognition and cell adhesion carry the HNK-1 epitope, 5'-nucleotidase may play a role in cell-cell or cell-extracellular matrix interaction in addition to its activity as an enzyme.

5'-Nucleotidase↗
PubMed1991

Identification of valine/leucine/isoleucine and threonine/alanine/glycine proton-spin systems of Escherichia coli adenylate kinase by selective deuteration and selective protonation.

Adenylate kinase from two types of Escherichia coli strains, a wild-type and a leucine-auxotrophic strain, was purified. On the one hand, growing the leucine-auxotrophic bacteria on a medium containing deuterated leucine yielded E. coli adenylate kinase with all leucine residues deuterated. On the other hand, by growing the wild-type bacteria on deuterated medium with phenylalanine, threonine and isoleucine present as protonated specimens, 80% randomly deuterated enzyme with protonated phenylalanine, threonine and isoleucine residues could be prepared. Use of these proteins enabled identification of the spin systems of these amino acid residues in the n.m.r. spectra of the protein.

Adenylate Kinase↗
PubMed1991

Occlusion of liver veins (Budd-Chiari syndrome) in childhood: a case report.

The Budd-Chiari syndrome is a rare cause of portal hypertension during childhood. We report on a 2-year-old boy suffering from liver congestion and ascites. No cause for the occlusion of the liver veins was found. There was an almost complete occlusion of the subdiaphragmatic vena cava due to compression by a hypertrophic lobus caudatus. Normal venous pressure could be demonstrated below this subtotal occlusion while numerous venous collaterals into the areas of the venae azygos and hemiazygos were encountered. A mesocaval shunt operation, therefore, seemed to be appropriate. There was, however, no decrease in production of ascites postoperatively. Repeat cavography now showed an elevation of venous pressure caused by the additional inflow of portal blood which could not, as expected, be compensated by caval collaterals. Therefore, a mesoatrial shunt was performed eight days after the first operation. However, even this additional shunt did not decrease the enormous production of ascites, and the child finally died. Hemodynamic and lymphodynamic pathways of the Budd-Chiari syndrome are discussed. Possibly a mesoatrial shunt in the first place, followed by a mesocaval shunt, would have been the better operative strategy.

Ascites↗
PubMed1990

Neurotransmitter release.

Axon terminals release more than one physiologically active substance. Synaptic messengers may be stored in two different types of vesicles. Small electron-lucent vesicles mainly store classical low molecular weight transmitter substances and the larger electron-dense granules store and release proteins and peptides. Release of the two types of substances underlies different physiological control. Release of messenger molecules from axon terminals is triggered by influx of Ca2+ through voltage sensitive Ca2+ channels and a rise in cytosolic Ca2+ concentrations. Neither the immediate Ca2+ target(s) nor the molecular species involved in synaptic vesicle docking, fusion and retrieval are known. It is, however, likely that steps involved in the molecular cascade of transmitter release include liberation of vesicles from their association with the cytonet and phosphorylation by protein kinase C of proteins which have the ability to alter between membrane bound and cytoplasmic forms and thus facilitate or initiate the molecular interaction between synaptic vesicles and the plasma membrane.

Animals↗
PubMed1979

5'-triphosphate recycles independently of acetylcholine in cholinergic synaptic vesicles.

The effect of hemicholinium-3 (HC-3) on vesicular contents in acetylcholine (ACh) and 5-triphosphate (ATP) and the vesicular incorporation of 14C-label derived from [14C]choline ,nd 3H-label derived from [3H]adenosine was investigated after low frequency stimulation (with a subsequent rest period) of the Torpedo electric organ. HC-3 (100 microM) caused an increased depletion of vesicular ACh and blocked the incorporation of 14C-label whereas contents in vesicular ATP and 3H-incorporation were identical with and without HC-3. HC-3 also blocked the recovery of electrical response of the tissue after stimulation but did not cause a change in vesicle numbers. The result suggest that synaptic vesicles continue to recycle ATP in the absence of recycling of ACh and that vesicular uptake and storage of the two components are not coupled to each other.

Acetylcholine↗