Structure-activity analysis of fluorinated 1-N-arylamino-1-arylmethanephosphonic acid esters as inhibitors of the NADH:ubiquinone oxidoreductase (complex I)

The structural and electronic properties of fluorinated 1-N-arylamino-1-arylmethanephosphonic acid esters were studied and related to the inhibitory effects on NADH:ubiquinone oxidoreductase (complex I). Electrostatic potential surfaces, dipole moments and molecular geometries were analysed. Based on the conformational analysis and the electronic parameters, a simple model for the active site of the fluorinated 1-N-arylamino-1-arylmethanephosphonic acid esters was developed, explaining the inhibitory power. The strongest inhibition effects were found for the 1-(N-4-trifluoromethoxyphenyl)-amino-1-phenylmethanephosphonic acid diethyl ester 1bab.

Thrombin inhibitors of bloodsucking animals

Hematophagous animals have the unique ability to inhibit blood coagulation when sucking blood from a wound. This article concerns thrombin inhibitors from these animals, specifically the one from the insect Rhodnius prolixus. To date, the most-studied inhibitor from these animals is hirudin, which specifically neutralizes thrombin but no other clotting serine proteases. The biochemical properties of hirudin are described. Hirudinlike thrombin inhibitors from the Asian leech Hirudo manillensis, Haemadipsa sylvestris, and Haemadipsidae are also discussed. In addition, a thrombin inhibitor from the insect Rhodnius prolixus, Rhodniin, is extensively reviewed. There is considerable interest in these inhibitors because they may be found useful as treatment modalities for thromboembolic disorders. Hirudin is already extensively investigated, and some of the others may follow. Potentially these new inhibitors could be of greater clinical benefit than the presently used heparins.

Identification of chitinase as the immunodominant filarial antigen recognized by sera of vaccinated rodents

Acanthocheilonema viteae is a parasitic nematode of rodents. We identified the chitinase of A. viteae infective stage larvae (L3) as the main target of the humoral immune response of jirds, which were protected against challenge infection after vaccination with irradiation attenuated L3. The cDNA of the L3 chitinase has been sequenced, and the deduced amino acid sequence shows significant homologies to chitinases of Brugia malayi microfilariae, insects, yeast, bacteria, and Streptomyces sp. The protein has been characterized by monoclonal antibodies and substrate activity gels. The chitinase of L3 may contribute to degrading the nematode cuticle during molting and thus represents a target of protective immune responses in a phase where the parasite is highly vulnerable. In addition, it has been shown that a similar enzyme exists in uterine microfilariae, which probably has a role in casting the egg shell.

Two heads are better than one: crystal structure of the insect derived double domain Kazal inhibitor rhodniin in complex with thrombin

Rhodniin is a highly specific inhibitor of thrombin isolated from the assassin bug Rhodnius prolixus. The 2.6 Angstrum crystal structure of the non-covalent complex between recombinant rhodniin and bovine alpha-thrombin reveals that the two Kazal-type domains of rhodniin bind to different sites of thrombin. The amino-terminal domain binds in a substrate-like manner to the narrow active-site cleft of thrombin; the imidazole group of the P1 His residue extends into the S1 pocket to form favourable hydrogen/ionic bonds with Asp189 at its bottom, and additionally with Glu192 at its entrance. The carboxy-terminal domain, whose distorted reactive-site loop cannot adopt the canonical conformation, docks to the fibrinogen recognition exosite via extensive electrostatic interactions. The rather acidic polypeptide linking the two domains is displaced from the thrombin surface, with none of its residues involved in direct salt bridges with thrombin. The tight (Ki = 2 x 10(-13) M) binding of rhodniin to thrombin is the result of the sum of steric and charge complementarity of the amino-terminal domain towards the active-site cleft, and of the electrostatic interactions between the carboxy-terminal domain and the exosite.

Increase in total protein following infection of CV-1 cells with SV40 virus as assayed by flow cytometry

The changes in cell size and total protein were determined for G1-arrested, contact-inhibited CV-1 cells infected with Simian virus 40 (SV40). The assays used were the Biorad total protein assays (Bradford and DC protein assays) on a standard number of cells, total protein as assayed by fluorescein isothiocyanate (FITC) and SR101 by flow cytometry, orthoganol (90 degrees) light scatter by flow cytometry, and direct microscopic measurement with an ocular micrometer. Uninfected CV-1 cells and two cell lines with variations in DNA content (diploid vs. tetraploid) were used as controls for the studies presented. The results demonstrated a 40-60% increase in total protein at 32 to 42 h postinfection. These increases were similar to values obtained due to cellular changes resulting from viral replication and cell death.

A randomized, double-blind, placebo-controlled, dose-ranging study of dofetilide in patients with inducible sustained ventricular tachyarrhythmias

INTRODUCTION

Dofetilide is a new antiarrhythmic agent with potent IK blocking properties in vitro. We developed a dose-ranging, placebo-controlled study design to define the range of effective doses and to evaluate the clinical electrophysiology of intravenous dofetilide in patients in whom sustained ventricular tachycardia or fibrillation was reproducibly inducible at baseline electrophysiologic testing.

METHODS AND RESULTS

The initial four patients received low doses that were increased in subsequent groups of four if adverse effects were absent. In each group of four patients, one patient was randomly assigned to placebo (double blind). Twenty-four patients were studied at six incremental loading and maintenance infusion regimens. Dofetilide (0.1 to 8.0 ng/mL) produced concentration-related increases in the % delta of QT (r = 0.79, P < 0.001), QTc (r = 0.60, P = 0.02), RR (r = 0.62, P < 0.02), and right ventricular effective refractory period (cycle length 600 msec; r = 0.68, P = 0.04). Placebo produced no changes in any of these measurements. Sustained ventricular tachycardia or ventricular fibrillation was no longer inducible in 1 of 6 patients receiving placebo and 8 of 18 receiving dofetilide (4 to 13 sec nonsustained ventricular tachycardia was induced in 4 of these 8). One patient developed torsades de pointes at a high concentration (5.3 ng/mL).

CONCLUSIONS

We conclude that: (1) dofetilide produces concentration-related IK blocking effects in patients; (2) an incremental dose-ranging study design aids in identifying the range of doses demonstrating electrophysiologic effects and efficacy; (3) a concomitant placebo group provides important data to assess reproducibility of results over time; and (4) further studies of dofetilide's efficacy and toxicity should be conducted.

The proton-pumping respiratory complex I of bacteria and mitochondria and its homologue in chloroplasts

The proton-pumping NADH:ubiquinone oxidoreductase, also called complex I, is the first of the respiratory complexes providing the proton motive force which is essential for the synthesis of ATP. Closely related forms of this complex exist in the mitochondria of eucaryotes and in the plasma membranes of purple bacteria. The minimal structural framework common to the mitochondrial and the bacterial complex is composed of 14 polypeptides with 1 FMN and 6-8 iron-sulfur clusters as prosthetic groups. The mitochondrial complex contains many accessory subunits for which no homologous counterparts exist in the bacterial complex. Genes for 11 of the 14 minimal subunits are also found in the plastidial DNA of plants and in the genome of cyanobacteria. However, genes encoding the 3 subunits of the NADH dehydrogenase part of complex I are apparently missing in these species. The possibility is discussed that chloroplasts and cyanobacteria contain a complex I equipped with a different electron input device. This complex may work as a NAD(P)H: or a ferredoxin:plastoquinone oxidoreductase participating in cyclic electron transport during photosynthesis.

Isolation and characterization of the proton-translocating NADH: ubiquinone oxidoreductase from Escherichia coli

The proton-translocating NADH:ubiquinone oxidoreductase (complex I) was isolated from Escherichia coli by chromatographic steps performed in the presence of an alkylglucoside detergent at pH 6.0. The complex is obtained in a monodisperse state with a molecular mass of approximately 550,000 Da and is composed of 14 subunits. The subunits were assigned to the 14 genes of the nuo operon, partly based on their N-terminal sequences and partly on their apparent molecular masses. The preparation contains one noncovalently bound FMN/molecule. At least two binuclear (N1b and N1c) and three tetranuclear (N2, N3 and N4) iron-sulfur clusters were detected by EPR in the preparation when reduced with NADH. Their EPR characteristics remained mostly unaltered during the isolation process. After reconstitution in phospholipid membranes, the preparation catalyses piericidin-A-sensitive electron transfer from NADH to ubiquinone-2 with Km values similar to those of complex I in cytoplasmic membranes but with only 10% of the Vmax value. The isolated complex I was cleaved into three fragments when the pH was raised from 6.0 to 7.5 and the detergent exchanged to Triton X-100. One of these fragments is a water-soluble NADH dehydrogenase fragment which is composed of three subunits bearing at least four iron-sulfur clusters (N1b, N1c, N3 and N4) that can be reduced with NADH, one of them bearing FMN. The second, amphipathic, fragment, which is presumed to connect the NADH dehydrogenase fragment with the membrane, contains four subunits and at least one EPR-detectable iron-sulfur cluster whose spectral properties are reminiscent of the eucaryotic cluster N2. The third membrane fragment is composed of seven homologues of the mitochondrially encoded subunits of the eucaryotic complex I. This subunit arrangement coincidences to some extent with the order of the genes on the nuo operon. A topological model of the E. coli complex I is proposed.

Two binding sites of inhibitors in NADH: ubiquinone oxidoreductase (complex I). Relationship of one site with the ubiquinone-binding site of bacterial glucose:ubiquinone oxidoreductase

The effect of ten naturally occurring and two synthetic inhibitors of NADH:ubiquinone oxidoreductase (complex I) of bovine heart, Neurospora crassa and Escherichia coli and glucose:ubiquinone oxidoreductase (glucose dehydrogenase) of Gluconobacter oxidans was investigated. These inhibitors could be divided into two classes with regard to their specificity and mode of action. Class I inhibitors, including the naturally occurring piericidin A, annonin VI, phenalamid A2, aurachins A and B, thiangazole and the synthetic fenpyroximate, inhibit complex I from all three species in a partially competitive manner and glucose dehydrogenase in a competitive manner, both with regard to ubiquinone. Class II inhibitors including the naturally occurring rotenone, phenoxan, aureothin and the synthetic benzimidazole inhibit complex I from all species in an non-competitive manner, but have no effect on the glucose dehydrogenase. Myxalamid PI could not be classified as above because it inhibits only the mitochondrial complex I and in a competitive manner. All inhibitors affect the electron-transfer step from the high-potential iron-sulphur cluster to ubiquinone. Class I inhibitors appear to act directly at the ubiquinone-catalytic site which is related in complex I and glucose dehydrogenase.

A competitive inhibitor assay for SV40 T/pRB complex formation employing extracts of SV40-transformed human lung cells

Simian virus 40 (SV40) large T antigen (T), a potent dominant oncogene product, forms a specific complex with the human retinoblastoma protein (pRb), a cellular growth suppressor. We have used a recombinant pRb fusion protein (GST-Rb) in combination with extracts from a line of SV40-transformed human lung cells (WI-26 VA4) to develop a simple, non-radioactive assay to rapidly screen for competitive inhibitors of T/pRb binding. We illustrate the use of the assay by demonstrating that several short peptides containing the signature sequence, Leu-X-Cys-X-Glu, can inhibit T/pRb complex formation. In contrast, peptides containing the related motif, Leu-X-Glu-X-Glu, including two peptides derived from the transcription factor E2F, are inactive in this assay. These results show that Glu cannot substitute for Cys in the Leu-X-Cys-X-Glu motif. This assay will facilitate the identification of agents that are inhibitors of T/pRb complex formation and that might exert effects on cellular growth regulation.

The gene locus of the proton-translocating NADH: ubiquinone oxidoreductase in Escherichia coli. Organization of the 14 genes and relationship between the derived proteins and subunits of mitochondrial complex I

The gene locus nuo of the proton-translocating NADH: ubiquinone oxidoreductase in Escherichia coli was identified by means of a DNA probe made by the polymerase chain reaction. The primers used for the reaction were derived from consensus sequences of the NAD(H)-binding subunit of mitochondrial NADH: ubiquinone oxidoreductase and the NAD(+)-reducing hydrogenase of Alcaligenes eutrophus. The nuo locus lies between minutes 49.2 and 49.6 on the E. coli chromosome and contains a cluster of 14 genes. They are bordered upstream by a sequence resembling sigma 70-dependent promoters and downstream by a sequence resembling rho-independent terminators. All 14 proteins derived from the nuo-genes are related to subunits of mitochondrial NADH: ubiquinone oxidoreductase, among which all subunits presumed to bind the substrates and to harbour the redox groups are found, as well as all seven mitochondrially encoded subunits. The E. coli enzyme seems to represent the minimal form of a proton-translocating NADH: ubiquinone oxidoreductase. The gene order in the nuo locus is conserved in comparison with other bacterial genomes and the chloroplast genome of higher plants. To some extent, the gene order correlates with the topological arrangement of the encoded subunits. The conception of modular evolution of NADH: ubiquinone oxidoreductase is further supported by the arrangement of the nuo-genes.

A Kazal-type inhibitor with thrombin specificity from Rhodnius prolixus

A thrombin-specific inhibitor with an apparent molecular mass of 11 kDa has been purified from the insect Rhodnius prolixus. Amino-terminal protein sequence analysis allowed the molecular cloning of the corresponding cDNA. The open reading frame codes for a protein of about 103 amino acid residues and displays an internal sequence homology of residues 6-48 with residues 57-101 indicating a two-domain structure. Based on the amino acid sequence the two domains exhibit high homology to protease inhibitors belonging to the Kazal-type family. Model building suggests that the first domain binds to the active site with residue His10 pointing into the specificity pocket. From gel filtration and tight-binding inhibition experiments the inhibitor appears to form 1:1 complexes with thrombin. Periplasma-directed heterologous expression of the rhodniin cDNA in Escherichia coli yields the intact thrombin inhibitor. Natural and recombinant rhodniin both display inhibition constants of about 2 x 10(-13) M.

Attempts to define distinct parts of NADH:ubiquinone oxidoreductase (complex I)

The NADH:ubiquinone oxidoreductase (complex I) is made up of a peripheral part and a membrane part. The two parts are arranged perpendicular to each other and give the complex an unusual L-shaped structure. The peripheral part protrudes into the matrix space and constitutes the proximal segment of the electron pathway with the NADH-binding site, the FMN and at least three iron-sulfur clusters. The membrane part constitutes the distal segment of the electron pathway with at least one iron-sulfur cluster and the ubiquinone-binding site. Both parts are assembled separately and relationships of the major structural modules of the two parts with different bacterial enzymes suggest, that both parts also emerged independently in evolution. This assumption is further supported by the conserved order of bacterial complex I genes, which correlates with the topological arrangement of the corresponding subunits in the two parts of complex I.

Bacterial NADH-quinone oxidoreductases: iron-sulfur clusters and related problems

Many bacteria contain proton-translocating membrane-bound NADH-quinone oxidoreductases (NDH-1), which demonstrate significant genetic, spectral, and kinetic similarity with their mitochondrial counterparts. This review is devoted to the comparative aspects of the iron-sulfur cluster composition of NDH-1 from the most well-studied bacterial systems to date.: Paracoccus denitrificans, Rhodobacter sphaeroides, Escherichia coli, and Thermus thermophilus. These bacterial systems provide useful models for the study of coupling Site I and contain all the essential parts of the electron-transfer and proton-translocating machinery of their eukaryotic counterparts.

Primary structure and functional expression of the omega-conotoxin-sensitive N-type calcium channel from rabbit brain

The complete amino acid sequence of a rabbit brain calcium channel (BIII) has been deduced by cloning and sequencing the cDNA. The open reading frame encodes 2339 amino acids, which corresponds to an M(r) of 261,167. A phylogenetic tree representing evolutionary relationships indicates that BIII is grouped together with the other rabbit brain calcium channels, BI and BII, into a subfamily that is distinct from the dihydropyridine-sensitive L-type subfamily. Transient expression in cultured skeletal muscle myotubes derived from muscular dysgenic mice demonstrates that the BIII channel mediates an omega-conotoxin-sensitive calcium current with kinetics and voltage dependence like those previously reported for whole-cell N-type current. Cell-attached patch recordings, with isotonic barium as the charge carrier, revealed distinct single channels with an average slope conductance of 14.3 pS.

The binding domain structure of retinoblastoma-binding proteins

The retinoblastoma gene product (Rb), a cellular growth suppressor, complexes with viral and cellular proteins that contain a specific binding domain incorporating three invariant residues: Leu-X-Cys-X-Glu, where X denotes a nonconserved residue. Hydrophobic and electrostatic properties are strongly conserved in this segment even though the nonconserved amino acids vary considerably from one Rb-binding protein to another. In this report, we present a diagnostic computer pattern for a high-affinity Rb-binding domain featuring the three conserved residues as well as the conserved physico-chemical properties. Although the pattern encompasses only 10 residues (with only 4 of these explicitly defined), it exhibits 100% sensitivity and 99.95% specificity in database searches. This implies that a certain pattern of structural and physico-chemical properties encoded by this short sequence is sufficient to govern specific Rb binding. We also present evidence that the secondary structural conformation through this region is important for effective Rb binding.

L-dopa inhibits in vitro phosphorylation of melanoma glycoproteins

L-DOPA had no effect on the endogenous phosphorylation of proteins after extraction with 1% Triton X-100 from hamster melanoma. When proteins were purified further by wheat germ-agglutinin chromatography, however, a dramatic and dose-dependent inhibitory effect of DOPA on glycoprotein phosphorylation was observed in the presence of Mn+2.

Accumulation of the pre-assembled membrane arm of NADH:ubiquinone oxidoreductase in mitochondria of manganese-limited grown Neurospora crassa

The NADH:ubiquinone oxidoreductase (complex I) of mitochondria is constructed from two arms arranged perpendicular to each other. The peripheral arm protruding into the matrix contains the proximal section of the electron pathway, and the membrane arm with all mitochondrially encoded subunits contains the distal section of the electron pathway. When Neurospora crassa is grown under manganese limitation the formation of the peripheral arm is disturbed, but the membrane arm containing the iron-sulfur cluster N-2, is accumulated. An extra-polypeptide, assumed to be a chaperone, is found to be associated with this pre-assembled membrane arm.

Characterization of assembly intermediates of NADH:ubiquinone oxidoreductase (complex I) accumulated in Neurospora mitochondria by gene disruption

NADH:ubiquinone oxidoreductase, the respiratory chain complex I of mitochondria, is an assembly of some 25 nuclear-encoded and 7 mitochondrially encoded subunits. The complex has an overall L-shaped structure formed by a peripheral arm and an elongated membrane arm. The peripheral arm containing one FMN and at least three iron-sulphur clusters constitutes the NADH dehydrogenase segment of the electron pathway. The membrane arm with at least one iron-sulphur cluster constitutes the ubiquinone reducing segment. We are studying the assembly of the complex in Neurospora crassa. By disrupting the gene of a nuclear-encoded subunit of the membrane arm a mutant was generated that cannot form complex I. The mutant rather pre-assembles the peripheral arm with all redox groups and the ability to catalyse NADH oxidation by artificial electron acceptors. The final assembly of the membrane arm is blocked in the mutant leading to accumulation of complementary assembly intermediates. One intermediate is associated with a protein that is not present in the fully assembled complex I. The results demonstrate that the two arms of complex I are assembled independently on separate pathways, and gave a first insight into the assembly pathway of the membrane arm. It is also shown for the first time that the obligate aerobic fungus N. crassa can grow and respire without an intact complex I. Gene replacement in this fungus is therefore a tool for investigation of this complex.

Molecular cloning and characterization of a novel calcium channel from rabbit brain

The complete amino acid sequence of a novel calcium channel (designated BII) from rabbit brain has been deduced by cloning and sequencing the cDNA. The BII calcium channel is structurally more closely related to the BI calcium channel than to the cardiac and skeletal muscle L-type calcium channels. Blot hybridization analysis of RNA from different tissues and from different regions of the brain shows that the BII calcium channel is distributed predominantly in the brain, being abundant in the cerebral cortex, hippocampus and corpus striatum.

[Esthesioneuroblastoma with orbital invasion]

The authors report on an 83-years-old woman with esthesioneuroblastoma (ENB). The first clinical manifestation was an invasion of the suborbital and orbital region. ENB are local destructive tumours which seldom metastasize. Complete surgical excision, supplemented by irradiation therapy offers the highest cure rate. Relapses should be treated with individualized afterloading radiotherapy.

Incidence of pneumonia in mechanically ventilated patients treated with sucralfate or cimetidine as prophylaxis for stress bleeding: bacterial colonization of the stomach

Retrograde colonization of the oropharynx from the stomach by microaspiration of gastric fluid is a recently recognized phenomenon associated with increased gastric pH that may result in pneumonia during ventilation therapy. In a prospective study we investigated 104 mechanically ventilated patients in the intensive care unit who were receiving sucralfate (n = 49) or cimetidine (n = 55) for stress ulcer prophylaxis. The incidence of pneumonia was 45.5% (25 patients) in the cimetidine group and 26.5% (13 patients) in the sucralfate group (95% confidence interval 0.98 to 6.97; odds ratio 2.61; p = 0.0549). Mortality rates were 18.4% (9 patients) in the sucralfate group versus 25.5% (14 patients) in the cimetidine group (p = 0.48). The mean pH values of gastric aspirates were significantly lower in patients treated with sucralfate than in patients receiving cimetidine (p = 0.044). The number of colony-forming units of Enterobacteriaceae in gastric aspirates was also significantly lower in the sucralfate group (p = 0.0037).

[Serological diagnosis of cytomegalovirus-induced interstitial pneumonia in patients following bone marrow transplantation]

For diagnosis of the interstitial pneumonia conditioned by cytomegalovirus (CMV) an indirect immunofluorescence test was used to measure IgM and IgG antibodies to CMV in 369 serum specimens from 41 patients after bone marrow transplantation (BMT). An interstitial pneumonia conditioned by CMV was diagnosed in 5 patients either serological (4 patients) or by detection of cytomegaloviral infection typical inclusion bodies in lung cells (1 patient). The detection of antibodies to CMV for diagnosis of interstitial pneumonia conditioned by CMV is problematical in the phase immediately after BMT because bone marrow recipients are severely immunosuppressed by radiation and cytotoxic drugs received before transplantation. New method for detection of CMV-specific antigens are necessary.

Structural characterization of a 14-residue peptide ligand of the retinoblastoma protein: comparison with a nonbinding analog

The retinoblastoma protein, a 110-kDa nuclear anti-oncoprotein, complexes specifically with transforming proteins of several oncogenic DNA viruses. A peptide [NLFCSEEMPSSDDE] derived from one of the viral proteins (simian virus 40 large T antigen) is known to competitively bind retinoblastoma protein, but a mutant analog [NLFCSKEMPSSDDE] does not. We studied the T peptide with HPLC to determine whether it can dimerize, and we employed circular dichroism spectroscopy to determine whether both peptides can exist in stable secondary structural conformations. HPLC analyses revealed that the T peptide is subject to oxidation and readily dimerizes. Circular dichroism analyses showed that both peptides can be induced to form stable secondary structural conformations under conditions that stabilize intramolecular hydrogen bonding in short peptides (90% 2,2,2-trifluoroethanol; 4 degrees C). The circular dichroism spectra of both peptide species were similar except for a statistically significant difference in the contour near 210 nm. Spectral analysis of the T-derived peptide species predicted elements of alpha-helix (18%), antiparallel beta-sheet (21%), beta-turn (22%) and unordered conformations (41%). An analysis of the mutant peptide species also predicted elements of alpha-helix (8%), antiparallel beta-sheet (28%), beta-turn (22%) and unordered conformations (40%). Thus, a small difference in the stabilized secondary structural conformations of the two sets of peptide species might partly explain their differential binding affinities for retinoblastoma protein, but it is likely that electrostatic charge differences resulting from the glutamic acid to lysine substitution play a dominant role.

Primary structure and functional expression from complementary DNA of a brain calcium channel

The primary structure of a voltage-dependent calcium channel from rabbit brain has been deduced by cloning and sequencing the complementary DNA. Calcium channel activity expressed from the cDNA is dramatically increased by coexpression of the alpha 2 and beta subunits, known to be associated with the dihydropyridine receptor. This channel is a high voltage-activated calcium channel that is insensitive both to nifedipine and to omega-conotoxin. We suggest that it is expressed predominantly in cerebellar Purkinje cells and granule cells.

Inhibition of the rat renal Na+/H+ exchanger by beta-adrenergic antagonists

The beta-adrenergic antagonists, alprenolol and propranolol, inhibit the Na+/H+ exchanger in rat renal brush-border membrane vesicles. Half-maximal inhibition occurs at 86 microM alprenolol and 36 microM propranolol. Similar to amiloride and Na+, propranolol protects the Na+/H+ exchanger from irreversible inhibition by the carboxyl group reagent, N,N'-dicyclohexyl-carbodiimide (DCCD). Protection is incomplete, depends on propranolol concentration, and reaches a maximum at 0.4 mM propranolol. With a comparable dose dependence, propranolol protects a 65 kDa band from labeling with [14C]DCCD. The data indicate that beta-adrenergic antagonists specifically interact with the proximal tubular Na+/H+ exchanger.

The same domain motif for ubiquinone reduction in mitochondrial or chloroplast NADH dehydrogenase and bacterial glucose dehydrogenase

The respiratory chain NADH:ubiquinone oxidoreductase (NADH dehydrogenase or Complex I) of mitochondria comprises some 30 different subunits, and one FMN and 4 or 5 iron-sulfur clusters as internal redox groups. The bacterial glucose dehydrogenase, which oxidizes glucose to gluconolactone in the periplasmatic space and transfers the electrons to ubiquinone, is a single polypeptide chain with pyrolloquinoline quinone as the only redox group. We report here that the two different enzymes have the same ubiquinone binding domain motif and we discuss the predicted membrane folding of this domain with regard to its role in the proton translocating function of the two enzymes.

A small isoform of NADH:ubiquinone oxidoreductase (complex I) without mitochondrially encoded subunits is made in chloramphenicol-treated Neurospora crassa

In mitochondria of Neurospora crassa grown in the presence of chloramphenicol a small form of NADH:ubiquinone reductase is made in place of the normal electron-transfer-complex I. This smaller enzyme has a molecular mass of approximately 350 kDa and consists of (at least) 13 different subunits which are all synthesized in the cytoplasm. The complex I which is normally found in Neurospora has a molecular mass of approximately 700 kDa and consists of around 30 different subunits, of which at least six are made in the mitochondria. Immunoblotting and peptide mapping suggest that the subunits of the small enzyme are homologous to subunits of the large enzyme, one subunit might even be identical. The small and the large NADH:ubiquinone reductases have the same high-affinity binding site for NADH but the two enzymes differ in the affinity and inhibitor sensitivity of the ubiquinone-binding site. The possibility is discussed that the small NADH:ubiquinone reductase is primitive isoform of complex I.

Synthesis of shock proteins in cultured fetal mouse myocardial cells

We examined the synthesis of shock proteins in cultured fetal mouse myocytes. The preparation is free from fibroblasts, and the cells are vital and morphologically intact with respect to beat frequency and electron microscopy. Cultured myocytes from fetal mouse heart respond to heat shock and cadmium chloride, H2O2, allylamine, cyclosporine, and azathioprine exposure with the synthesis of shock proteins. Heat shock induces the de novo synthesis of two proteins of 71 and 68 kDa; cadmium chloride induces, in addition, a protein of 30 kDa. The other substances tested provoke the synthesis only of the 30-kDa polypeptide. The formation of heat shock proteins is concentration-dependent: Cyclosporine provokes the de novo synthesis of the 30-kDa polypeptide at concentrations above 10 ng/ml, whereas azathioprine causes the same effect at concentrations above 50 micrograms/ml. Hence cyclosporine might be cardiotoxic already at concentrations below the pharmacological dosages while azathioprine influences the myocytes only at concentrations much higher than the therapeutic level. Our results indicate that heat shock protein expression in cultured myocytes may be a useful tool to monitor cardiotoxicity.