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At least 361 records · Page 20Linked to original sources
PubMed1973

Physiological effects of menaquinone deficiency in Bacillus subtilis.

Several aspects of the respiratory physiology of a mutant of Bacillus subtilis deficient in menaquinone-7 (MK-7) and in cytochromes were investigated. The mutant, an aromatic amino acid auxotroph blocked at dehydroshikimate reductase, is unable to synthesize MK-7 unless grown in the presence of the common aromatic amino acid intermediate, shikimate. The inability to synthesize MK-7 prevents the mutant from expressing the normal postexponentialphase cytochrome phenotype. When grown in the presence of shikimate, normal levels of these electron transport components are formed. It was found that the intracellular concentration of MK-7 could be predictably regulated by growing the cells with known concentrations of exogenous shikimate. When the mutant was grown under conditions where MK-7 biosynthesis was severely limited, there was a decrease in oxygen uptake and in membrane-associated reduced nicotinamide adenine dinucleotide (NADH) oxidase and succinate oxidase activity. NADH oxidase, but not succinoxidase, could be restored in membrane preparations by the addition of menadione to the reaction mixture. Reduced-minus-oxidized cytochrome difference spectra indicate that an MK-7 deficiency limits electron flow through the cytochrome chain. Furthermore, oxidation-reduction patterns suggest that MK-7 functions between the primary dehydrogenases and the cytochromes. Although the mutant is asporogenous when grown under conditions where MK-7 biosynthesis is limited, the inability to sporulate does not appear to result from lesions in the electron transport system.

Alcohol Oxidoreductases↗
PubMed1981

[Aggregation and separability of the shikimate pathway enzymes in yeasts].

Gel filtration was employed to estimate the molecular weights and to determine possible physical aggregation of enzymes [5-dehydroquinate synthase (DHQ synthase), 5-dehydroquinase (DHQase, EC 4.2.1.10), shikimate: NADP oxidoreductase (EC 1.1.1.25), shikimate kinase (EC 2.7.1.71), 3-enolpyruvylshikimate 5-phosphate synthase (EPSP synthase)] in the shikimate pathway in eleven species of yeasts. The five enzymes were not aggregated in extracts of Hansenula henricii, H. fabianii, H. anomala, Candida utilis, Pichia guilliermondii, and Lodderomyces elongisporus. Two enzymes (DHQase and shikimate:NADP oxidoreductase) were not separable by this method and by ion exchange chromatography, and we conclude that they exist as an aggregate in these yeasts. Evidence is presented for an enzyme aggregate containing five activities, with a molecular weight of approximately 280,000 in Rhodosporidium spaerocarpum, Rh. toruloides, Rhodotorula rubra, Saccharomycopsis lipolytica, and Saccharomyces cerevisiae. Similarities between the enzymes in the shikimate pathway of plants, bacteria, and other fungi and those of investigated yeasts are discussed.

3-Phosphoshikimate 1-Carboxyvinyltransferase↗
PubMed1998

Evidence for the shikimate pathway in apicomplexan parasites.

Parasites of the phylum Apicomplexa cause substantial morbidity, mortality and economic losses, and new medicines to treat them are needed urgently. The shikimate pathway is an attractive target for herbicides and antimicrobial agents because it is essential in algae, higher plants, bacteria and fungi, but absent from mammals. Here we present biochemical, genetic and chemotherapeutic evidence for the presence of enzymes of the shikimate pathway in apicomplexan parasites. In vitro growth of Toxoplasma gondii, Plasmodium falciparum (malaria) and Cryptosporidium parvum was inhibited by the herbicide glyphosate, a well-characterized inhibitor of the shikimate pathway enzyme 5-enolpyruvyl shikimate 3-phosphate synthase. This effect on T. gondii and P. falciparum was reversed by treatment with p-aminobenzoate, which suggests that the shikimate pathway supplies folate precursors for their growth. Glyphosate in combination with pyrimethamine limited T. gondii infection in mice. Four shikimate pathway enzymes were detected in extracts of T. gondii and glyphosate inhibited 5-enolpyruvyl shikimate 3-phosphate synthase activity. Genes encoding chorismate synthase, the final shikimate pathway enzyme, were cloned from T. gondii and P. falciparum. This discovery of a functional shikimate pathway in apicomplexan parasites provides several targets for the development of new antiparasite agents.

3-Phosphoshikimate 1-Carboxyvinyltransferase↗
PubMed2004

Molecular models for shikimate pathway enzymes of Xylella fastidiosa.

The Xylella fastidiosa is a bacterium that is the cause of citrus variegated chlorosis (CVC). The shikimate pathway is of pivotal importance for production of a plethora of aromatic compounds in plants, bacteria, and fungi. Putative structural differences in the enzymes from the shikimate pathway, between the proteins of bacterial origin and those of plants, could be used for the development of a drug for the control of CVC. However, inhibitors for shikimate pathway enzymes should have high specificity for X. fastidiosa enzymes, since they are also present in plants. In order to pave the way for structural and functional efforts towards antimicrobial agent development, here we describe the molecular modeling of seven enzymes of the shikimate pathway of X. fastidiosa. The structural models of shikimate pathway enzymes, complexed with inhibitors, strongly indicate that the previously identified inhibitors may also inhibit the X. fastidiosa enzymes.

Amino Acid Sequence↗
PubMed1978

Purification of two forms of the associated 3-dehydroquinate hydro-lyase and shikimate:NADP+ oxidoreductase in Phaseolus mungo seedlings.

Two associated enzymes, 3-dehydroquinate hydro-lyase (EC 4.2.1.10) and shikimate:NADP+ oxidoreductase (EC 1.1.1.25), have been purified from Phaseolus mungo seedlings. These enzymes were purified 6900- and 9700-fold, respectively, but they were not separable. Moreover, two activity bands of the shikimate:NADP+ oxidoreductase were detected after polyacrylamide gel electrophoresis and the two peaks also have 3-dehydroquinate hydro-lyase activity. The two forms of the associated enzymes showed only small differences in molecular weight, Km value, pH optimum and the responses to some inhibitors.

Alcohol Oxidoreductases↗
PubMed1978

Purification and characterization of 3-dehydroquinate hydrolase and shikmate oxidoreductase. Evidence for a bifunctional enzyme.

The basis for the physical association of 3-dehydroquinate dehydratase (3-dehydroquinate hydrolyase, EC 4.2.1.10) and shikimate dehydrogenase (shikimate: NADP+ 3-oxidoreductase, EC 1.1.1.25) in higher plants was investigated. The enzymes were extracted from the moss Physcomitrella patens and were purified to homogeneity. Determinations of subunit sizes were made by sodium dodecyl sulfate gel electrophoresis and gel exclusion chromatography in 6 M guanidinium chloride. Results from these studies demonstrate that both enzyme activities are carried out by a single polypeptide.

Alcohol Oxidoreductases↗
PubMed1972

Direct induction in wild-type Neurospora crassa of mutants (qa-1 c ) constitutive for the catabolism of quinate and shikimate.

A color test has been developed for the selection and identification of mutants in Neurospora crassa, constitutive for the three normally inducible enzymes which convert quinate to protocatechuate. By this means seven such mutants have been recovered after ultra violet irradiation of wild type and have been shown to be allelic (or very closely linked) to the qa-1(C) mutants previously obtained by other means. Thus, the regulation of the synthesis of these three catabolic enzymes is indicated to be under the control of a single gene, qa-1(+).

Alcohol Oxidoreductases↗
PubMed1974

A new nicotinamide-adenine dinucleotide-dependent hydroaromatic dehydrogenase of Lactobacillus plantarum and its role in formation of (minus)t-3,t-4-dihydroxycyclohexane-c-1-carboxylate.

1. A new induced NAD-dependent hydroaromatic dehydrogenase was isolated from a cell-free extract of Lactobacillus plantarum 13a and purified 175-fold. 2. The enzyme catalyses the oxidation of (-)-quinate, (-)-shikimate, (-)-dihydroshikimate and (-)t-3,t-4-dihydroxycyclohexane-c-1-carboxylate with NAD(+), and the reverse action with NADH. 3. The K(m) values at the optimal pH10.0 for these substrates are 0.85, 0.75, 0.52 and 0.74mm respectively, and the corresponding values for NAD(+) are 0.45, 0.26, 0.34 and 0.36mm respectively. 4. The stereochemical requirements of the enzyme and the role it may play in the reduction of (-)-quinate to (-)t-3,t-4-dihydroxycyclohexane-c-1-carboxylate are discussed and a pathway is suggested.

Centrifugation↗
PubMed1976

The shikimate pathway. III. 3-dehydroquinate synthetase of E. coli. Mechanistic studies by kinetic isotope effect.

The conversion of 3-deoxy D-arabino heptulosonate 7-phosphate to 3-dehydroquinate by the 3-dehydroquinate synthetase from E. coli is characterized by a low but significant kinetic isotope effect for tritium carried in position-5 of DAHP, while no isotope effect was detectable for tritium in position-4. This effect was observed at different pH nad is interpreted as a result of theintermediary of a 5-ketonic form of the substrate, formed in a preliminary non limiting step during the enzymic cyclization reaction. A tentative scheme for the 3-DHQ synthetase reaction is proposed involving five steps: oxidation by NAD+ in position-5, phsophate elimination after enolization, reduction with precedently formed NADH and cyclization by attack of the 2-carbonyl by the C-7 methylene group.

Chemical Phenomena↗
PubMed2006

New insights on glyphosate mode of action in nodular metabolism: Role of shikimate accumulation.

The short-term effects of the herbicide glyphosate (1.25-10 mM) on the growth, nitrogen fixation, carbohydrate metabolism, and shikimate pathway were investigated in leaves and nodules of nodulated lupine plants. All glyphosate treatments decreased nitrogenase activity rapidly (24 h) after application, even at the lowest and sublethal dose used (1.25 mM). This early effect on nitrogenase could not be related to either damage to nitrogenase components (I and II) or limitation of carbohydrates supplied by the host plant. In fact, further exposure to increasing glyphosate concentrations (5 mM) and greater time after exposure (5 days) decreased nodule starch content and sucrose synthase (SS; EC 2.4.1.13) activity but increased sucrose content within the nodule. These effects were accompanied by a great inhibition of the activity of phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31). There were remarkable and rapid effects on the increase of shikimic and protocatechuic (PCA) acids in nodules and leaves after herbicide application. On the basis of the role of shikimic acid and PCA in the regulation of PEPC, as potent competitive inhibitors, this additional effect provoked by glyphosate on 5-enolpyruvylshikimic-3-phosphate synthase enzyme (EPSPS; EC 2.5.1.19) inhibition would divert most PEP into the shikimate pathway, depriving energy substrates to bacteroids to maintain nitrogen fixation. These findings provide a new explanation for the effectiveness of glyphosate as a herbicide in other plant tissues, for the observed differences in tolerance among species or cultivars, and for the transitory effects on glyphosate-resistant transgenic crops under several environmental conditions.

Carbohydrate Metabolism↗