[What is the role of compulsory ECT therapy today?]

Electro-convulsive therapy (ECT) has been effective for years, but it arouses opposition among patients and especially in the general public. ECT treatment is limited and compared to other medical treatment it is considered exceptional by the law, regulations and treatment personnel. A question arises as to the position of therapists regarding compulsory ECT treatment. A questionnaire was sent on this subject to all the units utilizing ECT in Israel. Opinions ranged from complete negation of compulsory ECT, to regarding such treatment as possible in cases when the patient is compulsorily hospitalized and/or when the patient's guardian supports this treatment. The authors' opinion is that the Law of Patients' Rights regarding special treatment when the patient is in extreme danger must be followed. The law requires that three physicians agree to the treatment, and compulsory treatment is no longer applicable when the danger passes. ECT treatment is important and imperative in certain conditions, especially conditions endangering patients' lives. In these conditions the law provides the authority to physicians to make decisions regarding treatment.

NADP(+)-isocitrate dehydrogenase gene expression and isozyme activity during citrus fruit development

The accumulation of citric acid and its decline toward fruit maturation is typical of citrus fruit. We studied NADP(+)-isocitrate dehydrogenase (NADP-IDH), an enzyme involved in citrate metabolism. A cDNA encoding the enzyme was cloned from lemon (Citrus limon) juice sac cells, and is the first-reported NADP-IDH from fruits. Sequence comparisons and phylogenetic analysis indicate that it most probably belongs to a monophyletic clade of plant cytosolic enzymes. The mRNA level in the juice sac cells was induced during lemon fruit growth, and increased by about 15-fold to a peak as the fruit neared maturation. Spectrophotometric assay of the NADP-IDH activity in the pulp during fruit development showed that in young fruit, most of the activity was associated with the mitochondrial preparation and that, as the fruit grew, the activity shifted to the soluble fraction. The two activities could also be distinguished by isozyme gel electrophoresis: while one isozyme was detected in the mitochondrial preparation of young fruit and declined later, the other was induced in the soluble fraction of older fruit and increased as the fruit grew. The increasing activity of NADP-IDH in the soluble fraction throughout fruit development correlated well with the increase in gene expression, which suggests that the soluble activity is regulated by the expression of the cytosolic NADP-IDH gene. The possible role of this form of the enzyme in citric acid catabolism in the pulp is discussed.

Fermentative metabolism in grape berries: isolation and characterization of pyruvate decarboxylase cDNA and analysis of its expression throughout berry development

The involvement of pyruvate decarboxylase (PDC) in the control of alcohol production during ripening of fruit tissues under aerobic conditions has been only partially studied. Enzymological studies showed a significant increase in PDC activity during the ripening of oranges and pears, concurrently with the induction of ethanol production. In tomato, on the other hand, the induction of ethanol production and ADH gene expression after the onset of ripening was not accompanied by induction of PDC activity. The isolation of PDC cDNA from fruits has not yet been reported, nor has its expression pattern during fruit development. We report here the isolation of a cDNA clone encoding for a grape PDC and the characterization of its expression throughout berry development. The pattern of PDC gene expression throughout berry development, combined with earlier findings on constitutive PDC activity in the berry, may suggest that PDC is not the limiting factor for the production of ethanol in the berry, which is induced only after the onset of berry ripening. Alternatively, the induction of ADH gene expression, which occurs only after the onset of ripening in both tomatoes and grape berries, may serve as a regulator of ethanol production in response to a ripening-related cue.

The transduction of the signal for grape bud dormancy breaking induced by hydrogen cyanamide may involve the SNF-like protein kinase GDBRPK

Alterations in gene expression during early stages of dormancy release in grapevine buds were analyzed to facilitate the identification of gene products that may mediate the signal transduction of a dormancy-release signal, or derepression of meristematic activity. In the present report we describe the identification of GDBRPK, a transcript for an SNF-like protein kinase that is up-regulated upon chemical induction of dormancy release by hydrogen cyanamide (HC). Since SNF and SNF-like protein kinases are known as sensors of stress signals, we hypothesize that GDBRPK may be involved in the perception of a stress signal induced by HC. We also describe a simultaneous and remarkable induction of both PDC and ADH transcripts that was observed shortly after HC application, and was of a transient nature. These data may imply that HC application leads to a transient respiratory stress, which likely results in a temporary increase in the AMP/ATP ratio. Since AMP is known as a stress signal that is sensed by SNF-like kinases, we suggest that the SNF-like GDBRPK could serve as the sensor of this signal.

Tim18p, a new subunit of the TIM22 complex that mediates insertion of imported proteins into the yeast mitochondrial inner membrane

Import of carrier proteins from the cytoplasm into the mitochondrial inner membrane of yeast is mediated by a distinct system consisting of two soluble 70-kDa protein complexes in the intermembrane space and a 300-kDa complex in the inner membrane, the TIM22 complex. The TIM22 complex contains the peripheral subunits Tim9p, Tim10p, and Tim12p and the integral membrane subunits Tim22p and Tim54p. We identify here an additional subunit, an 18-kDa integral membrane protein termed Tim18p. This protein is made as a 21.9-kDa precursor which is imported into mitochondria and processed to its mature form. When mitochondria are gently solubilized, Tim18p comigrates with the other subunits of the TIM22 complex on nondenaturing gels and is coimmunoprecipitated with Tim54p and Tim12p. Tim18p does not cofractionate with the TIM23 complex upon immunoprecipitation or nondenaturing gel electrophoresis. Deletion of Tim18p decreases the growth rate of yeast cells by a factor of two and is synthetically lethal with temperature-sensitive mutations in Tim9p or Tim10p. It also impairs the import of several precursor proteins into isolated mitochondria, and lowers the apparent mass of the TIM22 complex. We suggest that Tim18p functions in the assembly and stabilization of the TIM22 complex but does not directly participate in protein insertion into the inner membrane.

Characterization of disulfide cross-links between fragments of proteolyzed Na,K-ATPase. Implications for spatial organization of trans-membrane helices

This study characterizes disulfide cross-links between fragments of a well defined tryptic preparation of Na,K-ATPase, 19-kDa membranes solubilized with C12E10 in conditions preserving an intact complex of fragments and Rb occlusion (Or, E., Goldshleger, R., Tal, D. M., and Karlish, S. J. D. (1996) Biochemistry 35, 6853-6864). Upon solubilization, cross-links form spontaneously between the beta subunit, 19- and 11.7-kDa fragments of the alpha subunit, containing trans-membrane segments M7-M10 and M1/M2, respectively. Treatment with Cu2+-phenanthroline (CuP) improves efficiency of cross-linking. Sequencing and immunoblot analysis have shown that the cross-linked products consist of a mixture of beta-19 kDa dimers ( approximately 65%) and beta-19 kDa-11.7 kDa trimers ( approximately 35%). The alpha-beta cross-link has been located within the 19-kDa fragment to a 6.5-kDa chymotryptic fragment containing M8, indicating that betaCys44 is cross-linked to either Cys911 or Cys930. In addition, an internal cross-link between M9 and M10, Cys964-Cys983, has been found by sequencing tryptic fragments of the cross-linked product. The M1/M2-M7/M10 cross-link has not been identified directly. However, we propose that Cys983 in M10 is cross-linked either to Cys104 in M1 or internally to Cys964 in M9. Based on this study, cross-linking induced by o-phthalaldehyde (Or, E., Goldshleger, R., and Karlish, S. J. D. (1998) Biochemistry 37, 8197-8207), and information from the literature, we propose an approximate spatial organization of trans-membrane segments of the alpha and beta subunits.

Metal-catalysed cleavage of Na,K-ATPase as a tool for study of structure-function relations

This paper describes a novel technique for specific cleavage of renal Na/K-ATPase, based on bound transition metal ions. The approach might have application to other P-type pumps or membrane proteins. In one type of experiment, specific cleavages of the alpha subunit have been observed following incubation with ascorbate plus H2O2. Five fragments with intact C-terminals and complementary fragments with intact N-terminals are detectable. The beta subunit is not cleaved. Cleavages depend on the presence of contaminant or added submicromolar concentrations of Fe2+ ions. The results suggest that Fe2+ (or Fe3+) binds with high affinity at the cytoplasmic surface and catalyze cleavages of peptide bonds close to the Fe2+ (or Fe3+) ion. The rate of cleavage is greatly affected by the conformational state of the protein, E1Na or E2(Rb), respectively. The findings provide information on spatial organization of the protein and suggest that the highly conserved regions of the alpha subunit, within the minor and major cytoplasmic loops, interact in the E2 or E2(Rb) conformations, but move apart in the E1 or E1Na conformations. In a second application of this technique, added Cu2+ ions at micromolar concentrations, have been shown to catalyse specific cleavages of both alpha and beta subunits at the extracellular surface. The experiments provide evidence for trans-membrane topology and proximity between trans-membrane segments M5-M10 within the alpha subunit and for interacting segments of alpha and beta subunits. We discuss the implications of metal-catalysed cleavages for spatial organisation of transmembrane helices of the protein.

Specific cross-links between fragments of proteolyzed Na,K-ATPase induced by o-phthalaldehyde

We have used o-phthalaldehyde (OPA) to cross-link adjacent fragments of "19 kDa membranes", a tryptic preparation of Na,K-ATPase lacking the ATP site but retaining cation occlusion sites. Treatment with OPA of "19 kDa membranes" or detergent-solubilized membranes containing occluded Rb ions [Or, E., Goldshleger, R., Tal, D. M., and Karlish, S. J. D. (1996) Biochemistry 35, 6853-6864] yielded cross-linked products of 25 and 31 kDa. Both species contained the 19 kDa fragment of the alpha subunit (transmembrane segments M7-M10). In addition, the 25 kDa product contained the fragment including M5-M6, while the 31 kDa product contained a 16 kDa fragment of the beta subunit. Cross-linking was unaffected by the absence or presence of ligands (Na, Rb, or Mg and ouabain). Cross-linking was largely abolished in thermally inactivated "19 kDa membranes". When proteolytic digestion of the 25 and 31 kDa products was combined with antibody binding, PKA-dependent phosphorylation, and sequencing of fragments, approximate positions of the cross-links were established. In the 25 kDa product, the cross-link was located within the short cytoplasmic segment Asn831-Arg841 of the 19 kDa fragment preceding M7 and within Ala749-Ala770 preceding M5. Thus, M7 and M5 are likely to be in close proximity. In the 31 kDa product, the cross-link was located in the extracellular loop of the alpha subunit between M7 and M8, close to residues which are known to interact with the beta subunit. Functional implications of the interactions between the fragments of the alpha (M5-M6 and M7-M10) and beta subunits are discussed.

The bacteriophage P1 lytic replicon: directionality of replication and cis-acting elements

We have identified the direction of replication of a bacteriophage P1 lytic replicon. This was accomplished by constructing lambda P1 lysogens that contain a functional P1 lytic replicon and analysing which of two nearby bacterial DNA markers flanking the lambda prophage were amplified when that replicon was activated. We demonstrate that both DNA markers are coordinately amplified, a result consistent with lytic replication proceeding in a bidirectional fashion. To analyze the role of various elements comprising the lytic replicon, we assessed the ability of a wild type replicon to complement a defective replicon that contains a transposon inserted between an essential lytic replication gene (repL) and the promoter (P53) at which transcription of that gene is initiated. We show that the wild type replicon cannot complement the mutant replicon. The simplest hypothesis to explain this result is that either P53 or repL protein functions primarily in cis for the replicon to operate.

Solubilization of a complex of tryptic fragments of Na,K-ATPase containing occluded Rb ions and bound ouabain

The nonionic detergent C12E10 (polyoxyethylene 10-laurylether) has been used to solubilize a complex of tryptic fragments of Na, K-ATPase containing occluded Rb ions and bound ouabain. The aim was to define which fragments are required to maintain Rb occlusion. The experiments utilize "19 kDa membranes" consisting of a 19 kDa and several smaller tryptic fragments (8-11.7 kDa) of the alpha subunit, which include trans-membrane segments M7/M10 and the pairs M1/M2, M3/M4, and M5/M6 [Capasso, J. M., et al (1992) J. Biol. Chem. 267, 1150-1158]. The beta subunit is partially split into a 16 kDa fragment and a glycosylated approximately 50 kDa fragment. Cation occlusion and ouabain binding are intact. After preincubation of "19 kDa membranes" with Rb (5 mM) and then ouabain (10 mM), 90-100% of occluded Rb was solubilized by C12E10 at 0 degrees C. All fragments of the alpha and beta subunits, and also the gamma subunit, were cosolubilized by C12E10, and were observed to sediment together on a sucrose density gradient as a complex containing occluded Rb ions. The soluble complex consists of a monomer containing one copy of each fragment, as indicated by size-exclusion HPLC, as well as estimates of specific Rb occlusion (20.0 +/- 1.2 nmol/mg of protein). In the absence of Rb ions and ouabain, the complex was unstable. Whereas the 19 kDa fragment (M7-M10) and beta subunit remained associated, the smaller fragments, containing M5/M6 and M3/M4 and M1/M2, and the subunit dissociated. Observations on the thermal inactivation of Rb occlusion, and effect of pH and ionic strength, suggest that the soluble complex is stabilized by multiple interactions, both within the lipid bilayer and in hydrophilic domains (e.g., salt bridges).

An effect of voltage on binding of Na+ at the cytoplasmic surface of the Na(+)-K+ pump

This work utilizes proteoliposomes reconstituted with renal Na(+)-K(+)-ATPase to study effects of electrical potential (40-80 mV) on activation of pump-mediated fluxes of Na+ or Rb+ (K+) ions and on inhibitory effects of Rb+ ions or organic cations. The latter include guanidinium derivatives that are competitive Na(+)-like antagonists (David, P., Mayan, H., Cohen, H., Tal, D. M., and Karlish, S.J.D. (1992) J. Biol. Chem. 267, 1141-1149). Cytoplasmic side-positive diffusion potentials significantly decreased the K0.5 of Na+ at the cytoplasmic surface for activation of ATP-dependent Na(+)-K+ exchange but did not affect the inhibitory potency of Rb+ (K+) or any Na(+)-like antagonist. Diffusion potentials did not affect activation of Rb(+)-Rb+ exchange by Rb+ ions at the cytoplasmic surface and had only a minor effect on Rb+ activation at the extracellular surface. Previously, we proposed that the cation binding domain consists of two negatively charged sites, to which two K+ or two Na+ ions bind, and one neutral site for the third Na+ (Glynn, I. M., and Karlish, S.J.D. (1990) Annu. Rev. Biochem. 59, 171-205). The present experiments suggest that binding of a Na+ ion in the neutral site at the cytoplasmic surface is sensitive to voltage. By contrast, binding of Rb+ ions at the extracellular surface of renal pumps appears to be only weakly or insignificantly affected by voltage. Inferences on the identity of the charge-carrying steps, based on experiments using proteoliposomes, are discussed in relation to recent evidence that dissociation of Na+ or association of K+ ions, at the extracellular surface, represent the major charge-carrying steps.

opaque-15, a maize mutation with properties of a defective opaque-2 modifier

An opaque mutation was identified that reduces gamma-zein synthesis in maize endosperm. The mutation, opaque-15, causes a 2- to 3-fold reduction in gamma-zein mRNA and protein synthesis and reduces the proportion of the 27-kDa gamma-zein A gene transcript. Although the protein bodies in opaque-15 are similar in size and morphology compared to wild type, there are fewer of them in developing endosperm cells. The opaque-15 mutation maps near the telomere of chromosome 7L, coincident with an opaque-2 modifier locus. Based on its phenotype, opaque-15 appears to be a mutation of an opaque-2 modifier gene.

opaque2 modifiers act post-transcriptionally and in a polar manner on gamma-zein gene expression in maize endosperm

The opaque2 (o2) modifier genes convert the soft endosperm of an o2 mutant to a hard, vitreous phenotype. The primary biochemical change associated with the expression of these genes is a two- to threefold increase in synthesis of the 27-kD gamma-zein storage protein. To investigate the mechanism of modifier gene activity, we examined the level of gamma-zein mRNA and protein synthesis during the early stages of endosperm development in normal, o2, and modified o2 geno-types. Although the o2 mutation was found to reduce expression of the 27-kD gamma-zein genes, the activity of o2 modifier genes dramatically increased the level of both gamma-zein protein and mRNAs as early as 16 days after pollination. At this stage, transcription of gamma-zein genes is reduced by approximately 50% in both o2 and modified o2 genotypes compared to wild type. Thus, it appears that the modifiers regulate gamma-zein synthesis through a post-transcriptional mechanism. Analysis of transcripts from the two nearly identical genes (A and B) encoding the 27-kD gamma-zein protein showed differences in the mRNA ratios in different genotypes. In modified o2 mutants, accumulation of A over B transcript was greatly enhanced during endosperm development. Somatic recombination at this locus was found to reduce the number of B genes in the endosperm, but this could not account for the preferential accumulation of the A transcript. Our results suggest that a product of the o2 modifier genes increases the translation or stability of the A gene mRNA, leading to enhanced synthesis of 27-kD gamma-zein protein.

Effects of competitive sodium-like antagonists on Na,K-ATPase suggest that cation occlusion from the cytoplasmic surface occurs in two steps

Information on cation occlusion sites of renal NA,K-ATPase has been obtained by comparing the ability of competitive Na-like antagonists (David, P., Mayan, H., Cohen, H., Tal, D. M., and Karlish, S. J. D. (1992) J. Biol. Chem. 267, 1141-1149) with that of transported alkali metal cations to protect against covalent modification and structural perturbations of the protein. Sodium antagonists include p- or m-xylylenebisguanidium, guanidinium ions, and ethylenediamine. Experiments with proteoliposomes reconstituted with Na,K-ATPase demonstrate that p-xylylenebisguanidium has pronounced selectivity for the cytoplasmic surface. Tryptic digestion of Na,K-ATPase leading to "19-kDa membranes," a specifically truncated enzyme with intact cation occlusion sites, requires the presence of alkali metal cations. Sodium antagonists do not protect 19-kDa membranes against further digestion, and occlusion is destroyed. Incubation of 19-kDa membranes at 37 degrees C, in the absence of occluded ions, leads rapidly to loss of ability to occlude rubidium ions. Rubidium, sodium, or other alkali metal cations protect fully, whereas sodium antagonists do not protect against this thermal inactivation. Like the alkali metal cations, sodium antagonists protect Na,K-ATPase and, somewhat less effectively, 19-kDa membranes against inactivation by the carboxyl reagent N,N'-dicyclohexylcarbodiimide. Cation occlusion from the cytoplasmic surface is suggested to occur in two steps. In an initial recognition, either transported cations or sodium antagonists interact with carboxyl groups. The second step is selective for transported cations and involves occlusion of cations (either potassium or sodium ions) and a conformational change to a compact structure, which is resistant to proteolysis and thermal inactivation. Sodium antagonists are sterically hindered from becoming occluded and block Na,K-ATPase activity. Implications for the structural basis of cation specificity of the Na/K pump are discussed.

Oncogenic forms of the neu/HER2 tyrosine kinase are permanently coupled to phospholipase C gamma

The neu/HER2 proto-oncogene encodes a transmembrane tyrosine kinase homologous to receptors for polypeptide growth factors. The oncogenic potential for the presumed receptor is released through multiple genetic mechanisms including a specific point mutation, truncation at the extracellular domain and overexpression of the protooncogene. Here we show that all these modes of oncogenic activation result in a constitutively phosphorylated neu protein and an increase in tyrosine phosphorylation of a phosphatidylinositol-specific phospholipase (PLC gamma). The examined transforming neu/HER2 proteins, unlike the normal gene product, also co-immunoprecipitated with PLC gamma molecules. A kinase-defective mutant of a transforming neu failed to mediate both tyrosine phosphorylation and association with PLC gamma, suggesting direct interaction of the neu kinase with PLC gamma. This possibility was examined by employing a chimeric protein composed of the extracellular ligand-binding domain of the epidermal growth factor receptor and the neu cytoplasmic portion. The chimeric receptor mediated rapid ligand-dependent modification of PLC gamma on tyrosine residues. It also physically associated, in a ligand-dependent manner, with the phosphoinositidase. Based on the presented results we suggest that the mechanism of cellular transformation by the neu/HER2 receptor involves tyrosine phosphorylation and activation of PLC gamma.