Asbestos related health hazards among power plant workers.
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Aged↗
Biomedical subjects
A Finkelstein
Publications and source records attributed to A Finkelstein.
Skin blisters as a manifestation of oxazepam toxicity.
A 75 year-old comatous patient was admitted after ingestion of 200 mg oxazepam. Skin blisters, attributed to oxazepam toxicity, appeared on the left forearm the following day and regressed spontaneously nine days later.
Aged↗
Channels formed in phospholipid bilayer membranes by diphtheria, tetanus, botulinum and anthrax toxin.
Diphtheria, tetanus, botulinum, and anthrax toxin are multipartate toxins, one of the domains of which is (or is presumed to be) an enzyme. Cell intoxication requires that the enzymatic portion gain access to the cytosol via endocytosis into an acidic vesicle compartment of the cell. Translocation of the enzyme across the vesicular membrane is dependent on the low pH of the vesicle and involves another domain of the toxin; for each of these toxins, that domain is capable of forming channels in phospholipid bilayer membranes. These channels are large (greater than 12 A diameter) and voltage-gated, and the pH conditions required for their formation in lipid bilayers are similar to those existing in acidic vesicles and required for cell intoxication.
Antigens, Bacterial↗
Recombinant viruses as poultry vaccines.
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Animals↗
[Pentamidine inhalation for Pneumocystis carinii pneumonia in AIDS].
Pneumocystis carinii pneumonia (PCP) is the major cause of death in AIDS. The use of standard drugs for PCP is associated with a remarkably high rate of adverse reactions in AIDS patients. We treated a 35-year-old homosexual with a first episode of PCP with intravenous trimethoprim, 20 mg/kg, and sulfamethoxazole, 100 mg/kg and later with pentamidine injections. However medication had to be stopped because of severe side effects. A new method of therapy using aerosolized pentamidine (300 mg per inhalation, daily) was then applied successfully. The patient recovered and has been having prophylactic inhalations and getting azothymidine for the past 8 months. In studies on relatively small numbers of patients this treatment has been reported to give good results with only minor side effects. However, further data are needed, especially on the optimal characteristics of the generated aerosol and the best delivery system.
Acquired Immunodeficiency Syndrome↗
Anthrax toxin: channel-forming activity of protective antigen in planar phospholipid bilayers.
The three separate proteins that make up anthrax toxin--protective antigen (PA), edema factor (EF), and lethal factor (LF)--act in binary combinations to produce two distinct reactions in experimental animals: edema (PA + EF) and death (PA + LF). PA is believed to interact with a membrane receptor, and after proteolytic processing, to mediate endocytosis and subsequent translocation of EF or LF into the cytosol. PA can be separated, after mild trypsinolysis, into two fragments, PA65 (65 kDa) and PA20 (20 kDa). We demonstrate that trypsin-cleaved PA is capable of forming cation-selective channels in planar phospholipid bilayer membranes and that this activity is confined to the PA65 fragment; PA20, LF, and EF are devoid of channel-forming activity. These PA65 channels exhibit pH-dependent and voltage-dependent activity--a property reminiscent of the channels formed by the two-chain proteins diphtheria, tetanus, and botulinum toxins.
Antigens, Bacterial↗
Hydrostatic pressures developed by osmotically swelling vesicles bound to planar membranes.
When phospholipid vesicles bound to a planar membrane are osmotically swollen, they develop a hydrostatic pressure (delta P) and fuse with the membrane. We have calculated the steady-state delta P, from the equations of irreversible thermodynamics governing water and solute flows, for two general methods of osmotic swelling. In the first method, vesicles are swollen by adding a solute to the vesicle-containing compartment to make it hyperosmotic. delta P is determined by the vesicle membrane's permeabilities to solute and water. If the vesicle membrane is devoid of open channels, then delta P is zero. When the vesicle membrane contains open channels, then delta P peaks at a channel density unique to the solute permeability properties of both the channel and the membrane. The solute enters the vesicle through the channels but leaks out through the region of vesicle-planar membrane contact. delta P is largest for channels having high permeabilities to the solute and for solutes with low membrane permeabilities in the contact region. The model predicts the following order of solutes producing pressures of decreasing magnitude: KCl greater than urea greater than formamide greater than or equal to ethylene glycol. Differences between osmoticants quantitatively depend on the solute permeability of the channel and the density of channels in the vesicle membrane. The order of effectiveness is the same as that experimentally observed for solutes promoting fusion. Therefore, delta P drives fusion. When channels with small permeabilities are used, coupling between solute and water flows within the channel has a significant effect on delta P. In the second method, an impermeant solute bathing the vesicles is isosmotically replaced by a solute which permeates the channels in the vesicle membrane. delta P resulting from this method is much less sensitive to the permeabilities of the channel and membrane to the solute. delta P approaches the theoretical limit set by the concentration of the impermeant solute.
Hydrostatic Pressure↗
Water movement: does thermodynamic interpretation distort reality?
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Body Water↗
A hydroxide ion carrier in planar phospholipid bilayer membranes: (C6F5)2Hg (dipentafluorophenylmercury).
Although a number of molecules are known to function as current-carrying proton carriers across lipid bilayer membranes, no such hydroxide ion carriers have been found to date. We report that (C6F5)2Hg, which can function as a chloride ion carrier, can also carry a hydroxide ion. In 100 mM Na2SO4 solutions, membranes treated with (C6F5)2Hg are almost ideally selective for H+/OH- between pH 6.0 and 9.5. Membrane conductance varies linearly with [OH-] over this pH range and with the square of the (C6F5)2Hg concentration. The presumed current-carrying species is the dimer [(C6F5)2Hg]2OH-, which, along with the neutral molecule (C6F5)2Hg, shuttles back and forth within the bilayer. In 0.2 M NaCl at pH 9.5, the OH- and Cl- conductances are approximately equal. Thus, the carrier displays an approximately 10(4)-fold preference for OH- over Cl-.
Electric Conductivity↗
Fulminant Wilsonian hepatitis: difficulties in diagnosis and treatment.
We present herein the case of a 16-yr-old girl with fulminant Wilsonian hepatitis. Complications included renal tubular damage, hemolysis, marked hypocomplementemia and hypergammaglobulinemia, spontaneous bacterial peritonitis, and Candida sepsis. The difficulties in diagnosis and treatment are discussed.
Adolescent↗
The N-terminal half of the heavy chain of botulinum type A neurotoxin forms channels in planar phospholipid bilayers.
The heavy chain of botulinum type A neurotoxin forms channels in planar phospholipid bilayer membranes. Channel activity is confined to the N-terminal half of this chain; the C-terminal half is inactive. Channel activity is stimulated by low pH (4.5-5.5) on the cis side (the side to which protein is added), neutral pH on the opposite (trans) side, and cis positive voltages. These findings are strikingly similar to those previously reported for analogous fragments of diphtheria and tetanus toxins.
Botulinum Toxins↗
A very short peptide makes a voltage-dependent ion channel: the critical length of the channel domain of colicin E1.
Cleavage of colicin E1 molecules with a variety of proteases or with cyanogen bromide (CNBr) generates COOH-terminal fragments which have channel-forming activity similar to that of intact colicin in planar lipid bilayer membranes. The smallest channel-forming fragment obtained by CNBr cleavage of the wild-type molecule consists of the C-terminal 152 amino acids. By the use of oligonucleotide-directed mutagenesis, we have made nine mutants along this 152 amino acid peptide, in which an amino acid was replaced by methionine in order to create a new CNBr cleavage site. The smallest of the CNBr-cleaved C-terminal fragments with channel-forming activity, in planar bilayer membranes, was generated by cleavage at new Met position 428 and has 94 amino acids, whereas a 75 amino acid peptide produced by cleavage of a new Met at position 447 did not have channel activity. The NH2-terminus of the channel-forming domain of colicin E1 appears therefore to lie between residues 428 and 447. Since, however, the last six C-terminal residues of the colicin can be removed without changing activity, the number of amino acids necessary to form the channel is 88 or less. In addition, the unique Cys residue in colicin E1 was replaced by Gly, and nine mutants were then made with Cys placed at sequential locations along the peptide for eventual use as sulfhydryl attachment sites to determine the local environment of the replaced amino acid. In the course of making 21 mutants, eight charged residues have been replaced by uncharged Met or Cys without changing the biological activity of the intact molecule. It has been proposed previously that the conformation of the colicin E1 channel is a barrel formed from five or six alpha-helices, each having 20 amino acids spanning the membrane and two to four residues making the turn at the boundary of the membrane. Our finding that 88 amino acids can make an active channel, combined with recently reported stoichiometric evidence that the channel is a monomer excludes this model and adds significant constraints which can be used in building a molecular model of the channel.
Amino Acid Sequence↗
Gating of a voltage-dependent channel (colicin E1) in planar lipid bilayers: the role of protein translocation.
The voltage-dependent channel formed in planar lipid bilayers by colicin E1, or its channel-forming C-terminal fragments, is susceptible to destruction by the nonspecific protease pepsin under well-defined conditions. In particular, pepsin acts only from the cis side (the side to which colicin has been added) and only upon channels in the closed state. Channels in the open state are refractory to destruction by cis pepsin, and neither open nor closed channels are destroyed by trans pepsin. Colicin E1 channels are normally turned on by cis positive voltages and turned off by cis negative voltages. For large (greater than 80 mV) positive voltages, however, channels inactivate subsequent to opening. Associated with the inactivated state, some channels become capable of being turned on by cis negative voltages and turned off by cis positive voltages, as if the channel-forming region of the molecule has been translocated across the membrane. Consistent with this interpretation is the ability now of trans pepsin to destroy these "reversed" channels when they are closed, but not when they are open, whereas cis pepsin has no effect on them in either the open or closed state. Our results indicate that voltage gating of the E1 channel involves translocation of parts of the protein across the membrane, exposing different domains to the cis and trans solutions in the different channel states.
Alkanes↗
Gating of a voltage-dependent channel (colicin E1) in planar lipid bilayers: translocation of regions outside the channel-forming domain.
C-terminal fragments of colicin E1, ranging in mol wt from 14.5 to 20 kD, form channels with voltage dependence and ion selectivity qualitatively similar to those of whole E1, placing an upper limit on the channel-forming domain. Under certain conditions, however, the gating kinetics and ion selectivity of channels formed by these different E1 peptides can be distinguished. The differences in channel behavior appear to be correlated with peptide length. Enzymatic digestion with trypsin of membrane-bound E1 peptides converts channel behavior of longer peptides to that characteristic of channels formed by shorter fragments. Apparently trypsin removes segments of protein N-terminal to the channel-forming region, since gating behavior of the shortest fragment is little affected by the enzyme. The success of this conversion depends on the side of the membrane to which trypsin is added and on the state, open or closed, of the channel. Trypsin modifies only closed channels from the cis side (the side to which protein has been added) and only open channels from the trans side. These results suggest that regions outside the channel-forming domain affect ion selectivity and gating, and they also provide evidence that large protein segments outside the channel-forming domain are translocated across the membrane with channel gating.
Colicins↗
The effect of methanethiol and methionine toxicity on the activities of cytochrome c oxidase and enzymes involved in protection from peroxidative damage.
The tissue changes characteristic of methionine toxicity may be caused by methanethiol (CH3SH) inhibition of enzymes involved in protection from peroxidative damage. Methanethiol is an intermediate of the transaminative pathway of methionine metabolism. Glutathione peroxidase, glutathione reductase, catalase and superoxide dismutase activities were therefore tested for susceptibility of CH3SH. Cytochrome c oxidase activity was also measured because of its known inhibition by mercaptans. A 10-min exposure to CH3SH depressed hepatic cytochrome c oxidase activity to 28% of the incubated control value, while hepatic, splenic and erythrocyte catalase activities were depressed, respectively, to 53, 52 and 71% of the incubated control. Similar reductions in catalase and cytochrome c oxidase activities were observed in rats fed a diet containing 3% L-methionine as compared to rats pair-fed a control diet containing 0.3% methionine. There was no difference in the amount of lipid peroxidation as monitored by the presence of malondialdehyde in the livers of these rats. In rats injected i.p. with 50 or 75 mumol of 3-methylthiopropionate, an intermediate of methionine catabolism, the maximum levels of exhaled methanethiol coincided with depressions in liver catalase and cytochrome c oxidase activity to 40-50% of control values. The activities of these enzymes returned to control values within 2 to 4 h. The inhibition of catalase activity does not appear to be the cause of the membrane damage observed in methionine toxicity.
Animals↗
Osmotic swelling of vesicles: its role in the fusion of vesicles with planar phospholipid bilayer membranes and its possible role in exocytosis.
In order for either lipid bilayer membranes or biological membranes to undergo fusion, stresses must somehow be generated in the region of membrane contact. In the fusion of phospholipid vesicles with planar bilayer membranes, the stress can be produced by osmotic swelling of vesicles contacting the planar membrane. On the other hand, fully swollen vesicles may be sufficiently stretched that the additional stress experienced from their adhesion to the planar membrane may in itself suffice to produce fusion (see also Rand & Parsegian, this volume). There is considerable circumstantial evidence that osmotic swelling of vesicles may also be a driving force in exocytosis. This evidence centers both on experiments demonstrating inhibition of exocytosis when vesicles are in a hyperosmotic medium, and on observations of vesicle swelling during the secretory process. This article has not reviewed all of the examples in the literature supporting an osmotic mechanism for fusion, but has attempted to suggest the diversity of cell types from which the examples are drawn and to indicate that the evidence is not conclusive. The unambiguous establishment of vesicle swelling prior to fusion would go far in establishing an osmotic mechanism of exocytosis. We must also be prepared to find that osmotic swelling may not be the only biological mechanism of stressing vesicle membranes contacting plasma membranes. The viral membrane fusion proteins provide the precedent for agents that can apparently sufficiently perturb membranes to cause fusion without any additionally imposed stresses, and even direct membrane mechanical stretching may act biologically as a fusogenic stress.
Animals↗
Channels formed by colicin E1 in planar lipid bilayers are large and exhibit pH-dependent ion selectivity.
The E1 subgroup (E1, A, Ib, etc.) of antibacterial toxins called colicins are known to form voltage-dependent channels in planar lipid bilayers. The genes for colicins E1, A and Ib have been cloned and sequenced, making these channels interesting models for the widespread phenomenon of voltage dependence in cellular channels. In this paper we investigate ion selectivity and channel size--properties relevant to model building. Our major finding is that the colicin E1 channel is large, having a diameter of at least 8 A at its narrowest point. We established this from measurements of reversal potentials for gradients formed by salts of large cations or large anions. In so doing, we exploited the fact that the colicin channel is permeable to both cations and anions, and its relative selectivity to them is a function of pH. The channel is anion selective (Cl- over K+) in neutral membranes, and the degree of selectivity is highly dependent on pH. In negatively charged membranes, it becomes cation selective at pH's higher than about 5. Experiments with pH gradients cross the membrane suggest that titratable groups both within the channel lumen and near the channel ends affect the selectivity. Individual E1 channels have more than one open conductance state, all displaying comparable ion selectivity. Colicins A and Ib also exhibit pH-dependent ion selectivity, and appear to have even larger lumens than E1.
Colicins↗
Channels formed by botulinum, tetanus, and diphtheria toxins in planar lipid bilayers: relevance to translocation of proteins across membranes.
The heavy chains of both botulinum neurotoxin type B and tetanus toxin form channels in planar bilayer membranes. These channels have pH-dependent and voltage-dependent properties that are remarkably similar to those previously described for diphtheria toxin. Selectivity experiments with anions and cations show that the channels formed by the heavy chains of all three toxins are large; thus, these channels could serve as "tunnel proteins" for translocation of active peptide fragments. These findings support the hypothesis that the active fragments of botulinum neurotoxin and tetanus toxin, like that of diphtheria toxin, are translocated across the membranes of acidic vesicles.
Botulinum Toxins↗