Structure of a 16 kDa integral membrane protein that has identity to the putative proton channel of the vacuolar H(+)-ATPase

A 16 kDa protein has been isolated in a homogeneous form as the major component of a paracrystalline paired membrane structure closely resembling the gap junction. The primary structure of this protein from arthropod and vertebrate species has been determined by protein and cDNA sequencing. The amino acid sequences are highly conserved and virtually identical to the amino acid sequence of the proteolipid subunit of the vacuolar H(+)-ATPases. The disposition of the protein in the membrane has been studied using proteases and the N,N'-dicyclohexylcarbodiimide reactive site identified. These data, together with secondary structure predictions, suggest that the 16 kDa protein is for the most part buried in the membrane, arranged in a bundle of four hydrophobic alpha-helices. Using computer graphics, a model has been constructed based on this arrangement and on the electron microscopic images of the paracrystalline arrays.

Identification by protein microsequencing of a proteinase-V8-cleavage site in a folding intermediate of chick muscle creatine kinase

We have identified by protein microsequencing a glutamic acid residue (Glu-166) in a folding intermediate of chick muscle creatine kinase that is very sensitive to cleavage by staphylococcal proteinase V8. Most other glutamic acid residues, including Glu-168, are already partly protected from proteolytic attack at this stage. After the final stages of protein refolding, when enzyme activity is recovered, Glu-166 is also resistant to proteolysis.

Double-ionization energies to ground and excited states of the tungsten hexacarbonyl dication

Tungsten hexacarbonyl was investigated by double-charge-transfer (DCT) spectroscoPy, and the double-ionization energies to ground and electronically excited states of W(CO) 6 (2+) determined. The double-ionization energies corresponding to the first two distinct peaks in the spectra are 22.8 ± 0.3 eV and 28.5 ± 0.3 eV, but numerous overlapping peaks at higher energies are evident. It is shown that the DeI spectra can explain the main features of a previously determined (J. Am. Soc. Mass Spectrom. 1990, 1, 16-27) internal energy distribution curve for W(CO) 6 (2+) ions formed by 70-eV electron ionization of W(CO)6 molecules.

Reversible accumulation of plant suspension cell cultures in g(1) phase and subsequent synchronous traverse of the cell cycle

The induction of DNA synthesis in Datura innoxia Mill. cell cultures was determined by flow cytometry. A large fraction of the total population of cells traversed the cell cycle in synchrony when exposed to fresh medium. One hour after transfer to fresh medium, 37% of the cells were found in the process of DNA synthesis. After 24 hours of culture, 66% of the cells had accumulated in G(2) phase, and underwent cell division simultaneously. Only 10% of the cells remained in G(0) or G(1). Transfer of cells into a medium, 80% (v/v) of which was conditioned by a sister culture for 2 days, was adequate to inhibit this simultaneous traverse of the cell cycle. A large proportion of dividing cells could be arrested at the G(0) + G(1)/S boundary by exposure to 10 millimolar hydroxyurea (HU) for 12 to 24 hours. Inhibition of DNA synthesis by HU was reversible, and when resuspended into fresh culture medium synchronized cells resumed the cell cycle. Consequently, a large fraction of the cell population could be obtained in the G(2) phase. However, reversal of G(1) arrested cells was not complete and a fraction of cells did not initiate DNA synthesis. Seventy-four percent of the cells simultaneously reached 4C DNA content whereas the frequency of cells which remained in G(0) + G(1) phase was approximately 17%. Incorporation of radioactive precursors into DNA and proteins identified a population of nondividing cells which represents the fraction of cells in G(0). The frequency of cells entering G(0) was 11% at each generation. Our results indicate that almost 100% of the population of dividing cells synchronously traversed the cell cycle following suspension in fresh medium.

Effects of cadmium on gene expression in cadmium-tolerant and cadmium-sensitiveDatura innoxia cells

The effect of Cd on gene expression in suspension cultures of twoDatura innoxia cell lines with differing Cd tolerance was studied.In vivo labeling experiments using [(3)H] leucine showed that Cd induced the synthesis of a similar range of proteins in both cell lines at a concentration which will kill the sensitive but not the tolerant cells. Corresponding changes in levels of translatable mRNA were also observed. The induction of the synthesis of proteins by Cd was transient since Cd-tolerant cells growing continuously in 250 μM CdCl2 contained a similar set ofin vitro translation products to cells growing in the absence of Cd. Although Cd had a similar effect on gene expression in both cell lines, Cd-tolerant cells possess two abundant mRNAs which are constitutively produced. These mRNAs encode proteins of low molecular weight (about 11 kDa) and are either absent or present at a low level in Cd-sensitive cells. The functions of these proteins are not known but they may be involved in the tolerance mechanism. Two-dimensional gel electrophoresis ofin vitro translation products showed that many of the Cd-induced proteins are also induced by heat shock. A 42°C heat shock resulted in agreater range and more intense induction of translatable mRNAs than 4 h exposure to 250 μM CdCl2. However a subset of mRNAs were induced specifically by Cd while other mRNAs were heat shock-specific. There was no difference in the ability of the two cell lines to tolerate heat shock. This was also reflected by the same pattern of major proteins induced by heat shock in the two cell lines.

Precursor-product relationships of Poly(γ-glutamylcysteinyl)glycine biosynthesis in Datura innoxia

Suspension cultures of Datura innoxia cells were pulse-labeled with [(35)S]cysteine, then exposed to Cd to determine whether there is a direct precursor-product relationship amongst the different forms of the Cd-induced polypeptides, poly(γ-glutamylcysteinyl)glycines [(γEC)nG, n=2 to 5]. Degradation of the polypeptides and possible regeneration of the [(35)S]-labeled glutathione and cysteine pools were also examined. After 2 h of exposure to [(35)S]cysteine, about 70% of the [(35)S]cysteine in the soluble fraction of the cell was incorporated into [(35)S]glutathione before exposure of the cells to Cd. One h after Cd exposure, most of the cellular [(35)S]glutathione was depleted and label was incorporated into (γEC)nG. Analysis of [(35)S](γEC)nG by reverse phase HPLC showed no direct precursor-product relationship between the synthesis of the shorter and longer chain forms. However, the rate of synthesis of the different polypeptides was linear for 32 h after Cd exposure. There was no evidence of degradation of [(35)S](γEC)nG nor was it excreted into the medium within this period. From these results it is suggested that in the presence of Cd, a large pool of (γEC)nG is unavailable for elongation to (γEC)n+1G.

Poly(gamma-glutamylcysteinyl)glycine Synthesis in Datura innoxia and Binding with Cadmium : Role in Cadmium Tolerance

The effects of Cd on poly(gamma-glutamylcysteinyl)glycine [(gammaEC)(n)G] biosynthesis and formation of (gammaEC)(n)G:Cd complexes were measured in two cell lines of Datura innoxia with differing Cd tolerance. In addition, RNA synthesis, protein synthesis, and GSH concentrations were measured during a 48 hour exposure to Cd. Exposure to 250 micromolar CdCl(2) was toxic to the sensitive line, whereas the tolerant line survived and grew in its presence. Cd-sensitive cells synthesized the same amount of (gammaEC)(n)G as tolerant cells during an initial 24 hour exposure to 250 micromolar CdCl(2). However, rates of (gammaEC)(n)G:Cd complex formation differed between the two cell lines with the sensitive cells forming complexes later than tolerant cells. In addition, the complexes formed by sensitive cells were of lower molecular weight than those of tolerant cells and did not bind all of the cellular Cd. Pulse-labeling of cells with l-[(35)S]cysteine resulted in equivalent rates of incorporation into the (gammaEC)(n)G of both cell lines during the initial 24 hours after Cd. Rates of protein and RNA synthesis were similar for both cell lines during the initial 8 hours after Cd but thereafter declined rapidly in sensitive cells. This was reflected by a decline in viability of sensitive cells. The GSH content of both cell lines declined rapidly upon exposure to Cd but was higher in sensitive cells throughout the experiment. These results show that the biosynthetic pathway for (gammaEC)(n)G synthesis in sensitive cells is operational and that relative overproduction of (gammaEC)(n)G is not the mechanism of Cd-tolerance in a Cd-tolerant cell line of D. innoxia. Rapid formation of (gammaEC)(n)G:Cd complexes that bind all of the cellular Cd within 24 hours appears to correlate with tolerance in these cells.

Purification and partial amino acid sequence of human urine protein 1. Evidence for homology with rabbit uteroglobin

We describe the purification of Urine Protein 1 (UP1), a 14-16 kDa protein which occurs in the urine of patients with renal failure, and therefore may originate from the plasma or kidney. Amino acid sequencing shows that UP1 has significant homology with rabbit uteroglobin, a secretory protein of the uterus (during pregnancy) and lungs (both sexes), and previously identified only in lagomorphs (rabbits, hares, pikas). The finding of a human uteroglobin-like protein, which can be purified from a readily available source, may provide further opportunities to elucidate the, as yet, uncertain physiological functions of uteroglobin.

A new role for histamine H2-receptors in asthmatic airways

Histamine tachyphylaxis develops with repeated inhalation of histamine in asthmatic subjects, and this appears to be due to the release of inhibitory prostaglandins. The purpose of this study was to determine whether histamine H2-receptors are also involved in the development of this protective effect in the airways. Seven subjects with mild asthma were studied on 2 days separated by at least 1 wk. On both days, three histamine inhalation tests were performed, separated by 1 h. The response was expressed as the provocative concentration of histamine causing a 20% decrease in FEV1 (histamine PC20). Before each study day subjects were pretreated with placebo or cimetidine (300 mg twice a day) for 3 days in a double-blind, randomized, crossover study. Cimetidine pretreatment had no effect on either baseline FEV1 or on baseline histamine PC20 (p = 0.461). After pretreatment with placebo, histamine tachyphylaxis occurred in all subjects; the mean PC20 increased from 3.01 mg/ml (%SD, 1.44) to 4.88 mg/ml (%SD, 1.68) and to 6.84 mg/ml (%SD, 1.68). Cimetidine pretreatment prevented histamine tachyphylaxis; the mean PC20 was 2.72 mg/ml (%SD, 1.77), 3.03 mg/ml (%SD, 1.73), and 3.56 mg/ml (%SD, 1.59) with repeated tests. These values differed significantly from placebo for both the second (p = 0.014) and third (p = 0.001) tests. This study demonstrated that cimetidine pretreatment prevents histamine tachyphylaxis and suggests that histamine tachyphylaxis occurs through stimulation of histamine H2-receptors in the airway.

Analysis of proteinuria using a commercial system for automated electrophoresis and isoelectric focusing

We describe an investigation of proteinuria using Pharmacia PhastSystemTM electrophoresis apparatus. The analysis of urinary proteins by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) of unconcentrated urine followed by silver staining took about 2 h and could clearly demonstrate tubular dysfunction or glomerular damage in urines with a negative or only trace-positive dip-stick test for protein. In addition, we show the identification of urinary proteins by immunoblotting from SDS-PAGE gels and the characterisation of Bence-Jones proteins by isoelectric focusing (IEF) and immunoblotting.

The mitochondrial ATP synthase inhibitor protein binds near the C-terminus of the F1 beta-subunit

The specific, mitochondrial ATP synthase protein (IF1) was covalently cross-linked to its binding site on the catalytic sector of the enzyme (F1-ATPase). The cross-linked complex was selectively cleaved, leaving IF1 intact to facilitate the subsequent purification of the F1 fragment to which IF1 was cross-linked. This fragment was identified by sequence analysis as comprising residues 394-459 on the F1 beta-subunit, near the C-terminus. This finding is discussed in the light of secondary structure predictions for both IF1 and the F1 beta-subunit, and sequence homologies between mitochondrial and other ATP synthases.

Poly(gamma-glutamylcysteinyl)glycine: its role in cadmium resistance in plant cells

Angiosperms can be selected for the ability to grow in the presence of normally toxic concentrations of certain trace metal ions. Addition of Cd and Cu to Cd-resistant Datura innoxia cell cultures results in the rapid synthesis and accumulation of sulfur-rich, metal-binding polypeptides. The structure of these compounds was determined using amino acid analysis, 13C NMR, and site-specific enzymic digestion. These compounds are poly(gamma-glutamylcysteinyl)glycines. Greater than 80% of the cellular Cd is bound to the bis and tris forms in Cd-resistant cells. There is a direct correlation between the maximum accumulation of the metal-binding polypeptides and the concentration of toxic ions to which the cells are resistant. In the presence of metal ions, the polypeptides form multimeric aggregates that can be resolved by gel chromatography. Cd binds to both the high and low molecular weight aggregates, whereas Cu preferentially binds to the higher molecular weight forms. The presence of gamma-carboxamide linkages between glutamyl and adjacent cysteinyl residues indicates that these polypeptides are products of biosynthetic pathways. Poly(gamma-glutamylcysteinyl)glycines bind metals and, in this respect, appear to be functional analogs of the protein metallothionein. However, in the absence of supraoptimal concentrations of trace metal ions, the functions of metallothionein in animals and microorganisms and poly(gamma-glutamylcysteinyl)glycines in plants may differ.

Characterization of metal binding peptides from cadmium resistant plant cells

The majority of the cellular cadmium (less than 80%) in cadmium resistant Datura innoxia cells is bound to a small, metal induced peptide which is not metallothionein. This peptide consists of glutamate, cysteine and glycine in a ratio between 2:2:1 and 3:3:1 and has an apparent molecular weight of 776, under denaturing conditions. It is heat stable and complexes with cadmium to produce multimeric forms which are separable by gel filtration. Chemical analyses suggest that some amino acids are not joined by classical peptide linkages. This indicates that the synthesis of the peptide may not be directed by mRNA and that induction of its synthesis may not involve increased transcription from a putative gene corresponding directly to this peptide. A smaller proportion (greater than 15%) of the cellular cadmium is bound to a larger compound which is also heat stable and binds copper more readily than cadmium in vivo. This larger compound has an amino acid composition similar, in some respects, to metallothioneins.

Interaction between the soluble F1 ATPase and its naturally occurring inhibitor protein. Studies using hydrophilic high-performance liquid chromatography and immunoelectron microscopy

Binding of the isolated ATPase (F1) to its naturally occurring inhibitor protein was studied by two novel, independent techniques. High-pressure gel permeation chromatography revealed one tight binding site (Kd = 0.46 microM) for the inhibitor on F1, and a number of weak, non-specific sites. Use of an antibody directed against a non-binding region of the inhibitor protein demonstrated the formation of inhibitor/F1/immunoglobulin G complexes of 1:1:1 and 2:2:1 stoichiometry, but not of the putatively more stable cyclic 4:2:2 complexes. It was concluded that, despite the presence of three beta-subunits, only one site per F1 molecule is available for binding its inhibitor protein.

Sites of protein-protein interaction on the mitochondrial F1-ATPase inhibitor protein

We have investigated the structure of the mitochondrial F1-ATPase inhibitor protein from ox heart by using a differential trace-labelling method. This method has also been used to determine sites on the inhibitor protein involved in binding to both the isolated mitochondrial ATPase (F1) and to a specific anti-inhibitor antibody. Native, free inhibitor was trace-labelled on its lysine and serine residues with [14C]acetic anhydride, and inhibitor protein unfolded in guanidinium chloride or specifically bound to another protein, with [3H]acetic anhydride. Exposure/concealment of residues was deduced from the 14C/3H ratios of the peptides in a proteolytic digest of the inhibitor, after separation by h.p.l.c. None of the lysine or serine residues in the native inhibitor are as exposed as in the unfolded form. There is a gradient of reactivity, with residues 54-58 being most concealed and exposure increasing towards either end of the protein. A slight decrease in reactivity is noted in residues 1-3, suggesting that the N-terminus may be in a fairly restricted environment. These findings are discussed in the light of the predicted structure of the inhibitor protein. All but one of the labelled residues increases in reactivity when inhibitor protein binds to F1. The exception, Lys-24, is only slightly concealed. Hence, F1 binding appears not to involve the lysine or serine residues directly. This finding is consistent with the view that the F1-inhibitor interaction is hydrophobic in nature. Complementary information was provided using an anti-inhibitor antibody that binds to a site on the inhibitor different from that at which F1 binds. Binding of this antibody conceals residues 54, 58, and 65 considerably. This confirms that F1 does not interact with these hydrophilic residues on the inhibitor protein.

Multiresidue method for quantitative determination of organophosphorus pesticides in foods

A multiresidue method for the quantitative determination of organophosphorus pesticides in foods from the Food and Drug Administration's Total Diet Study is described. The organophosphorus pesticides are separated on the basis of polarity and determined in both fatty and nonfatty foods with a minimum of interferences. The foods analyzed included raw and cooked individual foods as well as combination dishes, water, and whiskey. Recoveries of 17 organophosphorus pesticides in 41 foods ranged from about 80 to 118%.

Time-dependent changes in H1 content, H1 turnover, DNA elongation, and the survival of cells blocked in early S phase by hydroxyurea, aphidicolin, or 5-fluorodeoxyuridine

Cells were synchronized in G1 by isoleucine deprivation and then released into medium containing 1 mM hydroxyurea (HU), 5 micrograms mL-1 aphidicolin (APC), or 1 microgram mL-1 5-fluorodeoxyuridine (fl5dU). Coulter volume, content of histone H1 per unit DNA, turnover of histone H1, the extent of DNA elongation, and the survival of cells were measured as functions of time after release into the presence of the drugs. At the concentrations used in the experiments, the drug differ in their toxicity (fl5dU greater than HU greater than APC), induction of unbalanced cell growth, and the distribution of new DNA fragment sizes allowed during block, but they all (1) allow cells to enter S phase, (2) cause similar time-dependent losses of histone H1 per unit DNA, which begin as synchronized G1 cells begin to enter S phase, (3) retard DNA elongation beyond replicon size, and (4) retard the turnover of histone H1. The results indicate that loss of histone H1, inhibition of histone turnover, the retarded ligation of newly replicated DNA into bulk chromatin, and chromatin structural changes may be part of the cell's general response to inhibition of DNA replication. Since transient S phase block increases the frequencies of gene amplification [Mariani, B. D., & Schimke, R. T. (1984) J. Biol. Chem. 259, 1901-1910] and sister chromatid exchanges (SCE) [Rainaldi, G., Sessa, M. R., & Mariani, T. (1984) Chromosoma 90, 46-49], the observed changes in H1 content and chromatin organization may also be essential features of gene amplification and SCE.

Interaction between F1-ATPase and its naturally occurring inhibitor protein. Studies using a specific anti-inhibitor antibody

An antibody was raised to cross-linked ox-heart mitochondrial inhibitor protein, which cross-reacts with the free inhibitor but with no other mitochondrial membrane protein. This antibody yields an immunoprecipitate with the cross-linked inhibitor protein, but a soluble antibody-antigen complex with free inhibitor. The antibody binds well to inhibitor protein whether the latter is complexed with F1-ATPase or not. Antibody binding has no effect on the ability of the inhibitor protein to inhibit the ATPase activity of F1. These findings suggest that the antibody does not block the site of interaction between the inhibitor and F1. The inhibitor protein content of submitochondrial membrane preparations was determined by radioimmunoassay, activity measurements and an immunochemical 'back titration' technique. The inhibitor content of the membranes is shown to decrease after energisation, suggesting a loss of inhibitor from the membranes into solution. Binding antibody to the inhibitor protein on submitochondrial particles has no effect on the steady-state rate of phosphorylation, but it increases the lag phase preceding phosphorylation from 30 to 54 s. The rate constant for the approach to the steady state drops from 0.078 to 0.052 s-1. This effect confirms that the lag phase is due to inhibition of phosphorylation by the inhibitor protein. The increase in ATPase activity following energisation takes place by a fast phase (80% maximal activity reached within 90 s) and a slower phase (lasting about 10 min.). The rate constant of the rapid phase (0.017 s-1) is of the same order as that for the activation of phosphorylation. It is concluded that the rapid phase of ATPase induction is fast enough for this process to occur simultaneously with the activation of phosphorylation.

Selection, Isolation, and Characterization of Cadmium-Resistant Datura innoxia Suspension Cultures

Datura innoxia cells from suspension cultures were selected for their ability to grow and divide rapidly in normally lethal concentrations of cadmium. Cells resistant to 12.5, 25, 50, 100, 160, 200, and 250 micromolar cadmium chloride were isolated and utilized to initiate cell suspension cultures resistant to this toxic metal ion. Variant cell lines retained their ability to grow in cadmium after being grown in its absence for more than 400 generations. Resistance to cadmium was correlated with the synthesis of low molecular weight, cysteine-rich, cadium-binding proteins. Synthesis of these proteins was induced rapidly in cadmium-resistant cells in response to a challenge of cadmium. Induction was detectable within one hour after exposure of the cells to the metal ion. Accumulation of protein bound cadmium reached a maximum eight to twelve hours following exposure. Metal-binding proteins were not detectable in the cadmium sensitive D. innoxia cells from which resistant cells were derived.

Construction and analysis of DNA sequence libraries from flow-sorted chromosomes: practical and theoretical considerations

We describe the construction and analysis of recombinant DNA libraries representative of chromosomes 1 and 2 of Chinese hamster (Cricetulus griseus). Propidium-iodide stained chromosomes were purified by flow cytometric analysis and sorting, and EcoRI digests of purified DNA were cloned into the bacteriophage vector Charon 4A. These libraries contain DNA complementary to 63% and 69% of nick-translated DNA derived from flow-purified chromosomes 1 and 2, respectively. However, sequences complementary to only 24% and 35% of a total Chinese hamster genomic DNA tracer were hybridized in parallel renaturation experiments. The chromosome 2 library contained DNA sequences encoding dihydrofolate reductase (dhfr), a gene previously mapped to Chinese hamster chromosome 2. No sequences complementary to dhfr were found in the library constructed from chromosome 1 DNA. These analyses are discussed with regard to the current limitations and future strategies for the construction of chromosome-specific DNA sequence libraries of high purity and completeness.

Determination of 6-thiouric acid in human urine

A simple and rapid method is described for the determination of 6-thiouric acid in the urine of patients receiving azathioprine (Imuran, Burroughs Wellcome). The technique makes use of anion exchange column chromatography to isolate the 6-thiouric acid which is then measured by its absorption at 356 nm.

Binding of mitochondrial ATPase from ox heart to its naturally occurring inhibitor protein: localization by antibody binding

The naturally occurring ATPase inhibitor protein from ox heart mitochondria was cross-linked to its binding site on the mitochondrial ATPase using 1-ethyl-3-(dimethylamino)propyl carbodiimide. The cross-linked product, when transferred electrophoretically to a nitrocellulose sheet, reacted with antibodies directed against the inhibitor protein and the beta-subunit of the ATPase. It was concluded that the binding site for the inhibitor protein lies on the beta-subunit.