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PubMed1989

Aluminum-adenine nucleotides as alternate substrates for creatine kinase.

Aluminum-ATP has previously been shown to be a potent but selective inhibitor of certain kinases (N. C. Furumo and R. E. Viola (1989) Inorg. Chem. 28, 820-823). Because of the selective binding affinity that has been demonstrated, aluminum-ATP was examined as a potential alternate substrate for enzyme-catalyzed phosphoryl-transfer reactions. Of the kinases that have been examined only creatine kinase, which was weakly inhibited by Al-ATP, was found to utilize this metal-nucleotide complex as a substrate. The maximum velocity for this reaction is 0.6% of that observed with Mg-ATP, and a Michaelis constant of 90 microM was measured, which is comparable to that with Mg-ATP. The equilibrium constant for the reaction, measured by phosphorus-31 NMR spectroscopy, is 0.18. This value is indistinguishable from the value determined for the reaction with Mg-ATP as the phosphoryl donor. The rate of interconversion between reactants and products at stoichiometric levels of creatine kinase was found to be quite rapid in the presence of Al3+, indicating that the rate-limiting step in catalytic turnover for this substrate must be a slow rate of substrate binding and/or product release.

Adenosine Diphosphate↗
PubMed1994

Na+,K(+)-ATPase activity in CNS and noradrenergic neurotransmission: time course of differential desipramine (DMI) effects.

ATPase activities in CNS membranes were studied after administration of desipramine (DMI), a noradrenaline (NA) uptake inhibitor. In a previous paper we reported that Na+,K(+)-ATPase activity significantly increased 3 h after DMI administration (10 mg/kg) in hypothalamus and mesencephalus but not in cerebral cortex and pons-medulla oblongata membranes (Viola et al., Cell. molec. Neurobiol. 1989, 9, 263-271). Here it was observed that Na+,K(+)-ATPase increase induced by acute DMI disappeared at 24 h in hypothalamus but remained during 21 days in mesencephalus. Na+,K(+)-ATPase increase by acute DMI was inhibited when endogenous NA was depleted by the noradrenergic neurotoxin DSP-4 or the NA synthesis inhibitor alpha-methyl-p-tyrosine. On the whole, Mg(2+)-ATPase activity was not modified by treatment. 5'-nucleotidase, another membrane-bound enzyme, was unchanged by acute DMI. The addition of DMI in vitro (50 ng/mg tissue) during Na+,K(+)-ATPase assay failed to affect ATPase activities. Acute DMI effects on Na+,K(+)-ATPase are thus attributable to noradrenergic neurotransmission rather than to non-specific drug-CNS membrane interaction. Furthermore, DMI produces differential effects on membrane Na+,K(+)-ATPase, depending on treatment conditions and CNS area studied.

5'-Nucleotidase↗
PubMed2005

The effect of flavonol glycoside on the expressions of matrix metalloproteinase-1 in ultraviolet-irradiated cultured human skin fibroblasts.

Long-term and repeated exposure of ultraviolet (UV) light, a harmful environmental stress, on the skin often induces chronic skin diseases, such as skin cancer as well as photo-aging (premature skin aging), and the mechanisms of these skin damages are closely associated with up-regulation of matrix metalloproteinases (MMPs) activities. Here, we investigated the effect of quercetin-3-O-beta-d-(6''-feruloyl)-galactopyranoside isolated from the stems of Viola hondoensis (Violaceae) on the expression of MMPs in UV-irradiated human skin fibroblasts in vitro. Quercetin-3-O-beta-d-(6''-feruloyl)-galactopyranoside markedly reduced UV-induced MMP-1 expression at the protein levels in a dose-dependent manner. Our report is the first description for the ability of quercetin-3-O-beta-d-(6''-feruloyl)-galactopyranoside to regulate UV-induced MMP-1 expression.

Cells, Cultured↗
PubMed1995

Elimination of the sensitivity of L-aspartase to active-site-directed inactivation without alteration of catalytic activity.

The catalytic activity of the enzyme L-aspartase from Escherichia coli has previously been shown to be sensitive to sulfhydryl reagents. The use of group-specific reagents, and a sequence homology comparison study among the fumarase-aspartase family of enzymes, has not, however, lead to the identification of a specific, essential cysteinyl residue. We have recently shown that L-aspartate-beta-semialdehyde is an alternative substrate for L-aspartase, producing fumaric acid semialdehyde (FAA) which specifically inactivates the enzyme [Schindler, J. F., & Viola, R. E. (1994) Biochemistry 33, 9365]. Proteolytic digests of the resulting inactivated enzyme have now been mapped by HPLC and mass spectrometry. A specific residue (Cys-273) has been determined to be the site of FAA modification. Site-directed mutagenesis of this cysteine in the E. coli enzyme has produced altered enzymes which are considerably less sensitive to active-site-directed inactivation, while retaining full catalytic activity. Thus, cysteine-273 has been identified as an active-site nucleophile that, while not directly involved in catalysis in L-aspartase, is poised to attack an activated double bond in an enzyme-bound product analogue.

Amino Acid Sequence↗
PubMed2002

Crystal structure of F65A/Y131C-methylimidazole carbonic anhydrase V reveals architectural features of an engineered proton shuttle.

The crystal structure of F65A/Y131C murine alpha-carbonic anhydrase V (CAV), covalently modified at cysteine residues with 4-chloromethylimidazole, is reported at 1.88 A resolution. This modification introduces a methylimidazole (MI) group at residue C131 in the active site with important consequences. F65A/Y131C-MI CAV exhibits an up to 3-fold enhancement of catalytic activity over that of wild-type CAV [Earnhardt, J. N., Wright, S. K., Qian, M., Tu, C., Laipis, P. J., Viola, R. E., and Silverman, D. N. (1999) Arch. Biochem. Biophys. 361, 264-270]. In this modified CAV variant, C131-MI acts as a proton shuttle, facilitating the deprotonation of a zinc-bound water molecule to regenerate the nucleophilic zinc-bound hydroxide ion. A network of three hydrogen-bonded water molecules, across which proton transfer likely proceeds, bridges the zinc-bound water molecule and the C131-MI imidazole group. The structure of F65A/Y131C-MI CAV is compared to structures of Y64H/F65A murine CAV, wild-type human alpha-carbonic anhydrase II, and the gamma-carbonic anhydrase from Methanosarcina thermophilain an effort to outline common features of catalytic proton shuttles.

Animals↗
PubMed1996

Substrate specificity and identification of functional groups of homoserine kinase from Escherichia coli.

Homoserine kinase, an enzyme in the aspartate pathway of amino acid biosynthesis in Escherichia coli, catalyzes the conversion of L-homoserine to L-homoserine phosphate. This enzyme has been found to have broad substrate specificity, including the phosphorylation of L-homoserine analogs where the carboxyl functional group at the alpha-position has been replaced by an ester or by a hydroxymethyl group. Previous pH profile studies [Huo. X., & Viola, R. E. (1996) Arch. Biochem. Biophys. 330, 373-379] and chemical modification studies have suggested the involvement of histidinyl, lysyl, and argininyl residues in the catalytic activity of the enzyme. With the assistance of sequence alignments, several potential amino acids have been targeted for examination. Site-directed mutagenesis studies have confirmed a role for arginine-234 in the binding of the carboxyl group of L-homoserine, and the involvement of two histidine at the homoserine binding site. Mutations at these sites have led to the decoupling of the kinase activity from an inherent ATPase activity in the enzyme, and suggest the presence of independent domains for the binding of each substrate in homoserine kinase.

Amino Acid Sequence↗
PubMed1997

The structure of L-aspartate ammonia-lyase from Escherichia coli.

The X-ray crystal structure of l-aspartate ammonia-lyase has been determined to 2.8 A resolution. The enzyme contains three domains, and each domain is composed almost completely of alpha helices. The central domain is composed of five long helices. In the tetramer, these five helices form a 20-helix cluster. Such clusters have also been seen in delta-crystallin and in fumarase. The active site of aspartase has been located in a region that contains side chains from three different subunits. The structure of the apoenzyme has made it possible to identify some of the residues that are involved in binding the substrate. These residues have been examined by site-directed mutagenesis, and their putative roles have been assigned [Jayasekera, M. M. K., Shi, W., Farber, G. K., & Viola, R. E. (1997) Biochemistry 36, 9145-9150].

Aspartate Ammonia-Lyase↗
PubMed1997

Evaluation of functionally important amino acids in L-aspartate ammonia-lyase from Escherichia coli.

The high-resolution structure of l-aspartate ammonia-lyase from Escherichia coli has recently been determined [Shi, W., Dunbar, J., Jayasekera, M. M. K., Viola, R. E., & Farber, G. K. (1997) Biochemistry 36, 9136-9144]. An examination of the putative active site has been carried out, with the active site located in a cleft that contains the functionally significant lysine 327. A list of potential active site residues has been generated based on their proximity to this active site lysine, sequence homology comparisons with other members of the aspartase-fumarase enzyme family, and the necessity for chemically reasonable functionalities for the proposed roles. The five most likely candidates in the putative active site cleft have been examined by site-directed mutagenesis to test their feasibility for either substrate binding or acid-base catalytic roles. Arginine and lysine residues have been identified that appear to function in the orientation and binding of aspartic acid at the enzyme active site. Some tentative assignments have also been made of the acid and base catalytic groups that are proposed to be involved in the deamination reaction.

Amino Acids↗
PubMed2004

Reversible antifouling effect of the cyclotide cycloviolacin O2 against barnacles.

Cycloviolacin O2, a plant peptide of the cyclotide family, is shown to have potent effects against fouling barnacles (Balanus improvisus), with complete inhibition of settlement at a concentration of 0.25 microM. The effect of cycloviolacin O2 against barnacles is reversible and nontoxic in the bioassay employed in these studies. Cycloviolacin O2 was isolated from the terrestrial plant Viola odorata by strong cation exchange and reversed-phase HPLC and identified by mass spectrometry following aminoethylation and enzymatic cleavage.

Amino Acid Sequence↗
PubMed2001

Structural analyses of a malate dehydrogenase with a variable active site.

Malate dehydrogenase specifically oxidizes malate to oxaloacetate. The specificity arises from three arginines in the active site pocket that coordinate the carboxyl groups of the substrate and stabilize the newly forming hydroxyl/keto group during catalysis. Here, the role of Arg-153 in distinguishing substrate specificity is examined by the mutant R153C. The x-ray structure of the NAD binary complex at 2.1 A reveals two sulfate ions bound in the closed form of the active site. The sulfate that occupies the substrate binding site has been translated approximately 2 A toward the opening of the active site cavity. Its new location suggests that the low catalytic turnover observed in the R153C mutant may be due to misalignment of the hydroxyl or ketone group of the substrate with the appropriate catalytic residues. In the NAD.pyruvate ternary complex, the monocarboxylic inhibitor is bound in the open conformation of the active site. The pyruvate is coordinated not by the active site arginines, but through weak hydrogen bonds to the amide backbone. Energy minimized molecular models of unnatural analogues of R153C (Wright, S. K., and Viola, R. E. (2001) J. Biol. Chem. 276, 31151-31155) reveal that the regenerated amino and amido side chains can form favorable hydrogen-bonding interactions with the substrate, although a return to native enzymatic activity is not observed. The low activity of the modified R153C enzymes suggests that precise positioning of the guanidino side chain is essential for optimal orientation of the substrate.

Binding Sites↗
PubMed2004

Conserved structural and sequence elements implicated in the processing of gene-encoded circular proteins.

The cyclotides are the largest family of naturally occurring circular proteins. The mechanism by which the termini of these gene-encoded proteins are linked seamlessly with a peptide bond to form a circular backbone is unknown. Here we report cyclotide-encoding cDNA sequences from the plant Viola odorata and compare them with those from an evolutionarily distinct species, Oldenlandia affinis. Individual members of this multigene family encode one to three mature cyclotide domains. These domains are preceded by N-terminal repeat regions (NTRs) that are conserved within a plant species but not between species. We have structurally characterized peptides corresponding to these NTRs and show that, despite them having no sequence homology, they form a structurally conserved alpha-helical motif. This structural conservation suggests a vital role for the NTR in the in vivo folding, processing, or detoxification of cyclotide domains from the precursor protein.

Amino Acid Sequence↗
PubMed2007

A novel method of supplying nutrients permits predictable shoot growth and root : shoot ratios of pre-transplant bedding plants.

BACKGROUND AND AIMS: Growth of bedding plants, in small peat plugs, relies on nutrients in the irrigation solution. The object of the study was to find a way of modifying the nutrient supply so that good-quality seedlings can be grown rapidly and yet have the high root : shoot ratios essential for efficient transplanting. METHODS: A new procedure was devised in which the concentrations of nutrients in the irrigation solution were modified during growth according to changing plant demand, instead of maintaining the same concentrations throughout growth. The new procedure depends on published algorithms for the dependence of growth rate and optimal plant nutrient concentrations on shoot dry weight W(s) (g m(-2)), and on measuring evapotranspiration rates and shoot dry weights at weekly intervals. Pansy, Viola tricola 'Universal plus yellow' and petunia, Petunia hybrida 'Multiflora light salmon vein' were grown in four independent experiments with the expected optimum nutrient concentration and fractions of the optimum. Root and shoot weights were measured during growth. KEY RESULTS: For each level of nutrient supply W(s) increased with time (t) in days, according to the equation DeltaW(s)/Deltat=K(2)W(s)/(100+W(s)) in which the growth rate coefficient (K(2)) remained approximately constant throughout growth. The value of K(2) for the optimum treatment was defined by incoming radiation and temperature. The value of K(2) for each sub-optimum treatment relative to that for the optimum treatment was logarithmically related to the sub-optimal nutrient supply. Provided the aerial environment was optimal, R(sb)/R(o) approximately W(o)/W(sb) where R is the root : shoot ratio, W is the shoot dry weight, and sb and o indicate sub-optimum and optimum nutrient supplies, respectively. Sub-optimal nutrient concentrations also depressed shoot growth without appreciably affecting root growth when the aerial environment was non-limiting. CONCLUSION: The new procedure can predict the effects of nutrient supply, incoming radiation and temperature on the time course of shoot growth and the root : shoot ratio for a range of growing conditions.

Environment↗
PubMed2005

Relationships among growth, development and plastic response to environment quality in a perennial plant.

Phenotypic traits differ between plants in different environments and within individuals as they grow and develop. Comparing plants in different environments at a common age can obscure the developmental basis for differences in phenotype means in different environments. Here, we compared trait means and patterns of trait ontogeny for perennial (Viola septemloba) plants growing in environments that differed in quality either naturally or due to experimental manipulation. Consistent with predictions for adaptive stress resistance, plants grown in lower-quality environments allocated proportionately more biomass to roots and rhizomes, and produced smaller, thicker and longer-lived leaves. The developmental trajectory of almost all traits differed between environments, and these differences contributed to observed differences in trait means. Plants were able to alter their initial developmental trajectory in response to an increase in resources after 8 wk of growth. This result contrasts with previous findings, and may reflect a difference in the way that annual and perennial species respond to stress. Our results demonstrate the complexity of interactions between the environment and the development of the phenotype that underlie putatively adaptive plastic responses to environment quality.

Adaptation, Physiological↗
PubMed1990

Numerical analysis of electrophoretic periplasmic protein patterns, a possible marker system for epidemiologic studies.

The whole-cell and periplasmic protein (PP) compositions of 22 Serratia marcescens isolates were examined. Numerical analysis of whole-cell protein patterns was not a useful procedure for measuring relationships between organisms at the subspecific level. However, there was a very good correlation between electrophoretic PP pattern results and those obtained previously from multilocus enzyme electrophoresis (electrophoretic type) and biotype (D. Gargallo-Viola, J. Clin. Microbiol. 27:860-868, 1989). Clustering of isolates by using PP patterns compared by coefficients based on peak position (Dice coefficient) gave more precise information than that obtained by correlation coefficients. PP patterns appeared to be a useful tool that may be of value for epidemiologic studies.

Bacterial Proteins↗
PubMed2005

Regulation effect of 2',4',7-trihydroxyisoflavone on the expression of matrix metalloproteinase-1, 2 in ultraviolet-B irradiated primary cultured old aged human skin fibroblasts.

Long term and repeated exposure of UV light on the skin often induces chronic skin diseases such as skin cancer as well as photoaging, and the mechanisms of these skin damages are closely associated with up-regulation of matrix metalloproteinase's (MMPs) activities. We investigated the effect of 2',4',7-trihydroxyisoflavone purified from the whole plants of Viola hondoensis W. BECKER et H BOISSIEU (Violaceae) on the expression of MMPs in UV-B irradiated old aged human skin fibroblasts. 2',4',7-trihydroxyisoflavone markedly reduced UV-induced MMP-1 expression, but not MMP-2, at the both mRNA and protein levels in a dose-dependent manner. Our report is the first description for the ability of 2',4',7-trihydroxyisoflavone to regulate MMP-1 expression from ultraviolet-B irradiated primary cultured old aged human skin fibroblasts.

Cells, Cultured↗
PubMed2005

Swinging bridges of opportunity and challenges: memoirs of an African American nurse practitioner pioneer on providing primary care for the underserved.

This article presents the memoirs of Mrs. Viola D. Brown, RN, FNP, a pioneer African American nurse practitioner, on opportunities and challenges involved in providing primary and public health care for underserved populations in urban and rural areas of Kentucky. Mrs. Brown began her career with a visit to Mary Breckinridge and the Frontier Nursing Service, and she was elected into the University of Kentucky's Department of Public Health Hall of Fame in 2005. This article is an adapted version of the closing keynote address presented at the 13th Primary Care for the Underserved Conference held March 2005.

Black or African American↗
PubMed2005

Evaluation of fungicides for the control of carrot cavity spot.

Cavity spot is one of the most common and serious diseases of carrot (Daucus carota L). The disease, caused by different species of Pythium, including P. violae Chesters & Hickman, P. sulcatum Pratt & Mitchell and P. sylvaticum Campbell & Hendrix, leads to frequent high rejection rates during grading worldwide. In the area of the city of Québec, the disease is caused mainly by P. sulcatum, P. sylvaticum and P. macrosporum Vaartaja & van der Plaats-Niterink. Cavity spot can be controlled with metalaxyl, but reports are emerging that this treatment show little or no efficacy in many regions. This situation reinforces the need for alternative fungicides. The objectives of the present study were: (1) to determine the sensitivity of 14 pathogenic isolates of P. sulcatum, P. sylvaticum and P. macrosporum collected from carrots produced in the area of the city of Québec to different broad-spectrum and oomycete-specific fungicides (chlorothalonil, etridiazole, fludioxonil, fosetyl-Al, metalaxyl, zoxamide), (2) to evaluate the efficacy of the fungicides in controlling cavity spot, and (3) to evaluate the risk of resistance development of isolates with the best-performing fungicide(s). The determination of EC50 for the fungicides tested showed that most isolates were highly sensitive to both metalaxyl and zoxamide but insensitive to fludioxonil, fosetyl-Al and chlorothalonil. In greenhouse assays, only zoxamide provided significant and consistent disease control as measured by the number of cavity spot lesions caused by P. sulcatum. Investigations into the risk of resistance development to zoxamide showed that, for specific isolates, repeated exposure to the fungicide resulted in a loss of sensitivity.

Daucus carota↗
PubMed2004

Antibacterial activity of the Chinese traditional medicine, Zi Hua Di Ding.

The antibacterial activity of extracts from species of plants used in the Chinese medicine, Zi Hua Di Ding (Viola yedoensis, V. prionantha, Corydalis bungeana and Gueldenstaedtia verna), was tested against Bacillus subtilis and Pseudomonas syringae using a bioautographic assay. The petroleum ether and ethyl acetate extracts of all four species of plants showed activity against both species of bacteria, whereas the methanol and aqueous methanol extracts were inactive. Three fractions from the petroleum ether extracts of V. yedoensis, V. prionantha and C. bungeana showed activity against B. subtilis at 6.25 microg/mL. Preliminary analysis of these active fractions indicates that they contain long chain carboxylic acids.

Anti-Bacterial Agents↗