Biochemistry Commons^™

Biochemical Characterization Of Two Yeast Paralogous Proteins Mth1 And Std1, Satish Pasula

Dissertations

Glucose is the most abundant monosaccharide and preferred carbon and energy source for most cells. Many organisms have evolved sophisticated means to sense glucose and respond to it appropriately. The budding yeast, Saccharomyces cerevisiae senses glucose through two transmembrane proteins, Snf3 and Rgt2. In the presence of extracellular glucose Snf3 and Rgt2 generate an intracellular signal that leads to the degradation of Mthl and Stdl, thereby inducing the expression of hexose transporter genes (EXT) by inhibiting the function of Rgtl, a transcriptional repressor of HXT genes. Mthl and Stdl are degraded via the Yckl/2 Kinase-SCFGrrl-26S proteasome pathway triggered by the …

Characterization Of The Ompl1 Gene Of Pathogenic Leptospira Species In China And Cross-Immunogenicity Of The Ompl1 Protein, Haiyan Dong, Ye Hu, Feng Xue, Dexter Sun, David M. Ojcius, Yafei Mao, Jie Yan

All Dugoni School of Dentistry Faculty Articles

Background: The usefulness of available vaccine and serological tests for leptospirosis is limited by the low cross-reactivity of antigens from numerous serovars of pathogenic Leptospira spp. Identification of genus-specific protein antigens (GP-Ag) of Leptospira would be important for development of universal vaccines and serodiagnostic methods. OmpL1, a transmembrane porin of pathogenic leptospires, was identified as a possible GP-Ag, but its sequence diversity and immune cross-reactivity among different serovars of pathogenic leptospires remains largely unknown.

Results: PCR analysis demonstrated that the ompL1 gene existed in all 15 official Chinese standard strains as well as 163 clinical strains of pathogenic leptospires isolated …

Novel Xanthine And Oxanine Dna Glycosylase Activities In Yeast And Mammalian Systems, Liang Dong

All Dissertations

DNA that stores genetic information is frequently damaged in cells. The DNA bases carrying an exocyclic amino group [adenine (A), guanine (G), cytosine (C)] encounter deamination even under physiological conditions. Xanthine (X) and the newly discovered oxanine (O) are derived from deamination of guanine; they are potentially cytotoxic and mutagenic lesions. However, in yeast and eukaryotes, studies on the enzymatic repair of these lesions are limited.
In the yeast, Schizosaccharomyces pombe thymine-DNA glycosylase (Spo TDG) is homologous to human thymine-DNA glycosylase (hTDG), an enzyme that removes thymine from T/G pair. It was reported that Spo TDG contains uracil DNA glycosylase …

Dna Deamination Repair Enzymes In Bacterial And Human Systems, Rongjuan Mi

All Dissertations

DNA repair enzymes and pathways are diverse and critical for living cells to maintain correct genetic information. Single-strand-selective monofunctional uracil DNA glycosylase (SMUG1) belongs to Family 3 of the uracil DNA glycosylase superfamily. We report that a bacterial SMUG1 ortholog in Geobacter metallireducens (Gme) and the human SMUG1 enzyme are not only uracil DNA glycosylases (UDG), but also xanthine DNA glycosylases (XDG). Mutations at M57 (M57L) and H210 (H210G, H210M, H210N) can cause substantial reductions in XDG and UDG activities. Increased selectivity is achieved in the A214R mutant of Gme SMUG1 and G60Y completely abolishes XDG and UDG activity. Most …

Involvement Of Methyltransferases Enzymes During The Energy Metabolism Of The Anaerobic Archaeon Methanosarcina Semesiae Sp. Nov., Tj Lyimo

Tanzania Journal of Science

The methyl group transfer from dimethylsulfide (DMS), trimethylamine and methanol to 2-mercaptoethanesulfonic acid (coenzyme M) were investigated from cell extracts of Methanosarcina semesiae sp. nov. to evaluate whether the enzyme systems involved were constitutive or inductive. The extracts from cells grown on DMS exhibited methanogenic activity exclusively with DMS and methanethiol. Likewise when cells were pre-grown on trimethylamine or methanol the extracts only produced methane from the respective metaboilic substrate. Dimethylsulfide:methyl-coenzyme M transferase activity was dependent on ATP, but hydrogen did not stimulate activity. The fact that ATP could be replaced by the reductant Ti(III)-citrate indicates that reductive activation of …

The Proton-Translocating A Subunit Of F0f1-Atp Synthase Is Allocated Asymmetrically To The Peripheral Stalk., Monika G Düser, Yumin Bi, Nawid Zarrabi, Stanley D Dunn, Michael Börsch

Biochemistry Publications

The position of the a subunit of the membrane-integral F0 sector of Escherichia coli ATP synthase was investigated by single molecule fluorescence resonance energy transfer studies utilizing a fusion of enhanced green fluorescent protein to the C terminus of the a subunit and fluorescent labels attached to specific positions of the epsilon or gamma subunits. Three fluorescence resonance energy transfer levels were observed during rotation driven by ATP hydrolysis corresponding to the three resting positions of the rotor subunits, gamma or epsilon, relative to the a subunit of the stator. Comparison of these positions of the rotor sites with those …

Domain Compliance And Elastic Power Transmission In Rotary F(O)F(1)-Atpase., Hendrik Sielaff, Henning Rennekamp, André Wächter, Hao Xie, Florian Hilbers, Katrin Feldbauer, Stanley D Dunn, Siegfried Engelbrecht, Wolfgang Junge

Biochemistry Publications

The 2 nanomotors of rotary ATP synthase, ionmotive F(O) and chemically active F(1), are mechanically coupled by a central rotor and an eccentric bearing. Both motors rotate, with 3 steps in F(1) and 10-15 in F(O). Simulation by statistical mechanics has revealed that an elastic power transmission is required for a high rate of coupled turnover. Here, we investigate the distribution in the F(O)F(1) structure of compliant and stiff domains. The compliance of certain domains was restricted by engineered disulfide bridges between rotor and stator, and the torsional stiffness (kappa) of unrestricted domains was determined by analyzing their thermal rotary …

Alkoxyamine Polymers: Versatile Materials For Surface Ligation Applications, Lindsey Hines, Jessica Moore, David Dahl, Belinda Lady, Johnathan Brantley, Hasan Palandoken

Chemistry and Biochemistry

Immobilization of biomolecules (i.e., proteins, carbohydrates), on polymeric surfaces has been an area of intense research. The resultant bioconjugates often display increased stability, bioavailability and activity. Our research program seeks to explore the utility of the alkoxyamine (RONH2) functional group in new materials as versatile ligating sites for the immobilization of various compounds.

The ease with which alkoxyamines (RONH2) condense with aldehydes or ketones has prompted their widespread use in labelling liposome, bacterial and mammalian cell surfaces as well as chemoselectively ligating small molecule ‘recognition elements' onto polyfunctional substrates. These condensation reactions proceed in aqueous media to afford the robust …

Cariporide Prodrugs: Targeting Brain Cancer Cells Through Sodium-Proton Exchange Inhibition, Jacob Vervynckt, Johnathan Brantley, Jessica Moore, Mark Graves Ii, William Harley, Fredric A. Gorin, Hasan Palandoken

Chemistry and Biochemistry

More than 200,000 people in the United States are diagnosed with a primary or metastatic brain tumor annually. The life expectancy for these individuals is approximately 9-12 months from the time of diagnosis. This poor prognosis is due to the ineffectiveness of existing therapies (i.e., chemotherapy and radiotherapy) against brain cancer, where the primary problem is the inability to differentiate cancer cells from healthy brain cells.

Relative to healthy brain tissue, the heightened metabolism of cancer cells increases their reliance on the ion transport proteins NHE (sodium-proton exchanger) and NCX (sodium-calcium exchanger). Inhibition of these proteins disrupts the intricate pH …

Removal Of Benzaldehyde From Methanol Using Alkoxyamine Functionalized Silica Gel, Dino Sulejmanovic, Carrie Jo Pruitt, Eric Conte, Hasan Palandoken, Shing-Yi Suen

Chemistry and Biochemistry

Alkoxyamines (RONH₂) react readily with aldehydes and ketones to form stable oxime ethers, and, thus are expected to be excellent scavengers of these compounds. We installed alkoxyamines on silica gel surface to remove benzaldehyde from methanol. Silica gel was immersed in H₂O₂/H₂SO₄ solution to activate the surface. Activated silica gel was then reacted with 3-chloropropyltrichlorosilane. Displacement of the chloride with N-hydroxyphthalimide and subsequent treatment with hydrazine provided alkoxyamines on the surface of silica gel. The resulting silica gel surface with alkoxyamine functional groups was immersed in a 100 ppm benzaldehyde solution …

Molecular Characterisation Of A Bovine-Like Rotavirus Detected From A Giraffe, Emily Mulherin, Jill Bryan, Marijke Beltman, Luke O'Grady, Eugene Pidgeon, Lucie Garon, Andrew Lloyd, John Bainbridge, Helen O'Shea, Paul Whyte, Séamus Fanning

Department of Biological Sciences Publications

Background

Rotavirus (RV), is a member of the Reoviridae family and an important etiological agent of acute viral gastroenteritis in the young. Rotaviruses have a wide host range infecting a broad range of animal species, however little is known about rotavirus infection in exotic animals. In this paper we report the first characterisation of a RV strain from a giraffe calf.

Results

This report describes the identification and detailed molecular characterisation of a rotavirus strain detected from a 14-day-old Giraffe (Giraffa camelopardalis), presenting with acute diarrhea. The RV strain detected from the giraffe was characterized molecularly as G10P[11]. …

The Effects Of A Networked Data Acquisition System On Student Learning In General Chemistry Laboratories, Stuart C. Burris, Les L. Pesterfield, Darwin Dahl, Hasan Palandoken, Jacqueline Pope-Tarrence

Chemistry and Biochemistry

We have recently incorporated a networked data acquisition and analysis system into in our second semester general chemistry laboratories. Our investigation team has conducted a study to evaluate the effects of the networked data acquisition system on student performance on a Beer's Law laboratory. We focused on two specific phenomena: the effect of the networked data acquisition system on 1) student learning of specific content material and 2) student comfort level with laboratory work and data analysis. The study involved a networked data acquisition group (employing a UV-Vis spectrometer and colorimeters) and a control group (employing traditional, single wavelength spectrometers). …

Photocycloaddition Of Allenes, Crystal Ward

Theses and Dissertations

For the past ten years the Fleming research group has been involved in the research of allene compounds. We have explored the synthesis of allenes as well as several reactions involving allenes, such as oxidation and nitrene addition. Recently, we have explored the synthesis and photochemistry of allenic alcohols tethered to silicon. There are literature examples using allenes in synthesis, but very few examples exist using allenes in photochemical cycloaddition reactions. We have found that a diisopropylallenyloxy(cinnamyloxy)silane derivative undergoes [2+2] photochemical cycloaddition to produce a cyclobutylsilane product when irradiated for 60-75 minutes.

Polymer Supported Optical Biosensors, Ignacio Joseph Garcia

Electronic Theses and Dissertations

The use of various polymer supports adhering phospholipid multibilayers to an internal reflection element have been investigated. The polymer supports studied range from polystyrene (PS), and 100 nm wide PS nanospheres to triethylaminated poly(vinyl benzyl chloride) (PVBC). The PS nanospheres showed the most promise as an adhesion layer since they appear to be the most robust with repeated washings. They also appear to stabilize their adjacent phospholipid multibilayer by increasing the lipid melting temperature. The triethylaminated DVBC also provided an increase of lipid melting temperature, but not quite to the same degree as the PS nanospheres. The cooperativity of such …

Tethering Polypeptides Through Bifunctional Peg Cross-Linking Agents To Probe Protein Function: Application To Atp Synthase., Daniel J Cipriano, Stanley D Dunn

Biochemistry Publications

Chemical crosslinking mediated by short bifunctional reagents has been widely used for determining physical relationships among polypeptides in multisubunit proteins, but less often for functional studies. Here we introduce the approach of tethering polypeptides by using bifunctional reagents containing a lengthy, flexible PEG linker as a form of crosslinking especially suited to functional analyses. The rotary molecular motor ATP synthase was used as a model subject. Single cysteine residues were introduced into selected positions of ATP synthase epsilon subunit, a component of the rotor subcomplex of the enzyme, and the unrelated maltose binding protein (MBP), then the two purified recombinant …

An Inositolphosphorylceramide Synthase Is Involved In Regulation Of Plant Programmed Cell Death Associated With Defense In Arabidopsis, Wenming Wang, Xiaohua Yang, Samantha Tangchiaburana, Roland Ndeh, Jennifer E. Markham, Yoseph Tsegaye, Teresa M. Dunn, Guo-Liang Wang, Maria Bellizzi, James F. Parsons, Danielle Morrissey, Janis E. Bravo, Daniel V. Lynch, Shunyuan Xiao

Department of Biochemistry: Faculty Publications

The Arabidopsis thaliana resistance gene RPW8 triggers the hypersensitive response (HR) to restrict powdery mildew infection via the salicylic acid–dependent signaling pathway. To further understand how RPW8 signaling is regulated, we have conducted a genetic screen to identify mutations enhancing RPW8-mediated HR-like cell death (designated erh). Here, we report the isolation and characterization of the Arabidopsis erh1 mutant, in which the At2g37940 locus is knocked out by a T-DNA insertion. Loss of function of ERH1 results in salicylic acid accumulation, enhanced transcription of RPW8 and RPW8-dependent spontaneous HR-like cell death in leaf tissues, and reduction in plant stature. …

Global Analysis Of Gene Expression Changes During Retinoic Acid-Induced Growth Arrest And Differentiation Of Melanoma: Comparison To Differentially Expressed Genes In Melanocytes Vs Melanoma, Mary H. Estler, Goran Boskovic, James Denvir, Sarah Miles, Donald A. Primerano, Richard M. Niles

Biochemistry and Microbiology

BACKGROUND: The incidence of malignant melanoma has significantly increased over the last decade. Some of these malignancies are susceptible to the growth inhibitory and pro-differentiating effects of all-trans-retinoic acid (RA). The molecular changes responsible for the biological activity of RA in melanoma are not well understood.

RESULTS: In an analysis of sequential global gene expression changes during a 4-48 h RA treatment of B16 mouse melanoma cells, we found that RA increased the expression of 757 genes and decreased the expression of 737 genes. We also compared the gene expression profile (no RA treatment) between non-malignant melan-a mouse melanocytes and …

Simple Inhibitors Of Histone Deacetylase Activity That Combine Features Of Short-Chain Fatty Acid And Hydroxamic Acid Inhibitors, Jessica L. Tischler, Basel Abuaita, Sierra C. Cuthpert, Christopher Fage, Kristi Murphy, Andrew Saxe, Edward B. Furr, Jamie Hedrick, Jennifer Meyers, David Snare, Ali R. Zand

Chemistry & Biochemistry Publications

Butyric acid and trichostatin A (TSA) are anti-cancer compounds that cause the upregulation of genes involved in differentiation and cell cycle regulation by inhibiting histone deacetylase (HDAC) activity. In this study we have synthesized and evaluated compounds that combine the bioavailability of short-chain fatty acids, like butyric acid, with the bidentate binding ability of TSA. A series of analogs were made to examine the effects of chain length, simple aromatic cap groups, and substituted hydroxamates on the compounds' ability to inhibit rat-liver HDAC using a fluorometric assay. In keeping with previous structure-activity relationships, the most effective inhibitors consisted of longer …

Phosphorylation Of P27kip1 Regulates Assembly And Activation Of Cyclin D1-Cdk4, Michelle D. Larrea, Jiyong Liang, Thiago G. Da Silva, Feng Hong, Shan H. Shao, Kathy Han, D. Dumont, Joyce M. Slingerland

Chemistry and Physics Faculty Articles

p27 mediates Cdk2 inhibition and is also found in cyclin D1-Cdk4 complexes. The present data support a role for p27 in the assembly of D-type cyclin-Cdk complexes and indicate that both cyclin D1-Cdk4-p27 assembly and kinase activation are regulated by p27 phosphorylation. Prior work showed that p27 can be phosphorylated by protein kinase B/Akt (PKB/Akt) at T157 and T198. Here we show that PKB activation and the appearance of p27pT157 and p27pT198 precede p27-cyclin D1-Cdk4 assembly in early G₁. PI3K/PKB inhibition rapidly reduced p27pT157 and p27pT198 and dissociated cellular p27-cyclin D1-Cdk4. Mutant p27 allele products lacking phosphorylation at …

Molecular-Orientation-Dependent Ac Stark Effect And Its Impact On Multiphoton Processes, Xi Chu

Chemistry and Biochemistry Faculty Publications

We study the dependence of the ac Stark shifts of electronic energies on the molecular orientation relative to the polarization direction of an incident intense laser field, using a three-dimensional non-Hermitian Floquet method and H(2)+ as a model system. Simultaneously, we also study the orientation-dependent high-order harmonic generation (HHG) and multiphoton ionization (MPI). We find that with the presence of near-one-photon resonance, the Stark effect strongly mixes electronic states of different symmetries to create quasienergy states (QESs). The orientation dependence of multiphoton processes, in which these QESs play an important role, becomes complex. Population transfer is better achieved with aligned …

The Very-Long-Chain Hydroxy Fatty Acyl-Coa Dehydratase Pasticcino2 Is Essential And Limiting For Plant Development, Liên Bach, Louise V. Michaelson, Richard Haslam, Yannick Bellec, Lionel Gissot, Jessica Marion, Marco Da Costa, Jean-Pierre Boutin, Martine Miquel, Frédérique Tellier, Frederic Domergue, Jennifer E. Markham, Frederic Beaudoin, Johnathan A. Napier, Jean-Denis Faure

Department of Biochemistry: Faculty Publications

Very-long-chain fatty acids (VLCFAs) are synthesized as acyl-CoAs by the endoplasmic reticulum-localized elongase multiprotein complex. Two Arabidopsis genes are putative homologues of the recently identified yeast 3-hydroxy-acyl-CoA dehydratase (PHS1), the third enzyme of the elongase complex. We showed that Arabidopsis PASTICCINO2 (PAS2) was able to restore phs1 cytokinesis defects and sphingolipid long chain base overaccumulation. Conversely, the expression of PHS1 was able to complement the developmental defects and the accumulation of long chain bases of the pas2–1 mutant. The pas2–1 mutant was characterized by a general reduction of VLCFA pools in seed storage triacylglycerols, cuticular waxes, …

Oriented Cell Growth On Self-Assembled Bacteriophage M13 Thin Films, Jianhua Rong, L. Andrew Lee, Kai Li, Brandon Harp, Charlene M. Mello, Zhongwei Niu, Qian Wang

Faculty Publications

Fibrillar M13 bacteriophages were used as basic building blocks to generate thin films with aligned nanogrooves, which, upon chemical grafting with RGD peptides, guide cell alignment and orient the cell outgrowth along defined directions.

Sex- And Gonad-Affecting Scent Compounds And 3 Male Pheromones In The Rat, Jian-Xu Zhang, Lixing Sun, Jin-Hua Zhang, Zhi-Yong Feng

All Faculty Scholarship for the College of the Sciences

This study was aimed at identifying sex pheromones of the rat (Rattus norvegicus). We characterized the volatiles and semivolatiles of rat preputial gland and voided urine by using gas chromatography–mass spectrometry (GC–MS) and quantified them by their GC areas (abundances) and percentage of GC areas (relative abundances). Although all the compounds other than 4-heptanone and phenol detected were shared by males and females, the quantities for some of these sex-common compounds exhibited sexual dimorphism and decreased with gonadectomy. Thus, these compounds might be sex pheromones. Among them, squalene from preputial glands and 2-heptanone and 4-ethyl phenol from urine …

Spectroscopic Studies On Arabidopsis Ethe1, A Glyoxalase Ii-Like Protein, Meghan M. Holdorf, Brian Bennett, Michael W. Crowder, Christopher A. Makaroff

Physics Faculty Research and Publications

ETHE1 (ethylmalonic encephalopathy protein 1) is a β-lactamase fold-containing protein that is essential for the survival of a range of organisms. In spite of the apparent importance of this enzyme, very little is known about its function or biochemical properties. In this study Arabidopsis ETHE1 was over-expressed and purified and shown to bind tightly to 1.2 ± 0.2 equivalents of iron. ¹H NMR and EPR studies demonstrate that the predominant oxidation state of Fe in ETHE1 is Fe(II), and NMR studies confirm that two histidines are bound to Fe(II). EPR studies show that there is no antiferromagnetically coupled Fe(III)Fe(II) …

I. Thermodynamics And Magnetism Of Cu2ocl2 Ii. Repairs To Microcalorimeter The "2"S Are Subscripts, And The Second 2 Is Preceded By A Lower Case L, Not A One, Thomas J. Parry

Theses and Dissertations

Adiabatic calorimetry provides accurate and precise specific heat (Cp) data. From this data, thermodynamic functions may be calculated. Cu2OCl2, melanothallite, became of interest as part of a study of a particular thermochemical cycle. The experimental specific heat data and the calculated thermodynamic functions are reported here. Free energies of formation, calculated from the thermodynamic functions, suggest the particular cycle of interest with this compound as an intermediate is not feasible; uncertainty as to the accuracy of CuO and CuCl2 data used in the calculations indicate further study may be necessary. Upon collection of the specific heat data, an antiferromagnetic transition …

A Radical Conjugate Addition Approach To The Total Synthesis Of Celogentin C, Steven G. Capps

Theses and Dissertations

The synthesis of five chiral DBFOX (dibenzofuran-oxazoline) ligands with either aryl or benzyl substituents will be presented. The requisite amino alcohols were obtained with high enantioselectivity either commercially (DBFOX/Bn), via Sharpless asymmetric aminohydroxylation (DBFOX/Nap, DBFOX/t-BuPh, DBFOX/Pip), or via phase-transfer catalyzed asymmetric alkylation (DBFOX/MeNap). These ligands, complexed with Mg(NTf2)2, were used as Lewis acid promoters of enantioselective radical conjugate additions to α/β-unsaturated nitro-amides/esters. A summary of these results is presented and discussed. These findings led us to believe that our initial binding model between metal, ligand, and substrate was flawed. Thus, we figured that if we started with a functionality known …

Microbial Nitrogen Cycling In Nevada Geothermal Springs, Mitchell G. Chaires, Jeremy A. Dodsworth, Brian P. Hedlund

Undergraduate Research Opportunities Program (UROP)

Hot spring habitats above maximum photosynthetic temperature (73 ºC) are not well understood with respect to nitrogen (N) cycling. Few predictions have been made, and even fewer measurements of in situ activities have been reported. Thermodynamic calculations based on in situ chemical and temperature measurements will be used to predict the occurrence of the specific N-cycling reactions. In addition, these measurements in two springs will aid in an attempt to cultivate ammonia oxidizing species.

Regulators Of G-Protein Signaling, Rgs13 And Rgs16, Are Associated With Cxcl12-Mediated Cd4+ T Cell Migration, Lijin Xia

Theses and Dissertations

Chemokines are important chemical signals that guide lymphocyte movement within the immune system and promote the organization and functions of germinal centers (GCs) in the secondary lymphoid tissues. Previous studies have shown that GC T cells exhibit high expression of chemokine receptor 4, CXCR4, but that these cells are unable to migrate to the ligand for this receptor, the chemokine CXCL12. This “migratory paralysis” to CXCL12 was found to be correlated with the expression of two Regulators of G-protein Signaling, RGS13 and RGS16 in the GC T cells. The objective of my research was to determine whether RGS13 and RGS16 …

Altered Expression Of Cell Cycle And Apoptotic Proteins In Chronic Hepatitis C Virus Infection., Saira Sarfraz, Saeed Hamid, Anwar Ali Siddiqui, Snawar Hussain, Shahid Pervez, Graeme Alexander

Department of Biological & Biomedical Sciences

Background: A disrupted cell cycle progression of hepatocytes was reported in chronic hepatitis C virus (HCV) infection, which can contribute significantly in the associated pathogenesis. The present study aimed to further elaborate these disruptions by evaluating the expression of key cell cycle and apoptotic proteins in chronic HCV infection with particular reference to genotype 3. Archival liver biopsy specimens of chronic HCV-infection (n = 46) and normal histology (n = 5) were analyzed by immunohistochemistry using antibodies against proliferation marker Mcm-2, G1 phase marker Cyclin D1, S phase marker Cyclin A, cell cycle regulators p21 (CDK inhibitor) and p53 (tumor …

A Fluorescent Photoinduced Electron Transfer (Pet) Sensor For Cations With A Separate Pet Channel To Suppress Proton Signals, Supun Pathirana

Theses, Dissertations and Culminating Projects

This thesis presents A-((10-((2-methoxy-4-methylphenoxy)methyl)anthracen-9- yl)methyl)(pyridin-2-yl)-A-((pyridin-2-yl)methyl)methanamine, 1, a photoinduced electron transfer (PET) sensor that acts as a fluorescent ‘Off-On’ switch in the presence of Zn ions and not sensitive to protons.