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R K Scopes

Publications and source records attributed to R K Scopes.

At least 55 records · Page 3Linked to original sources
PubMed1987

A simple device for automated spectrophotometric kinetics using a diode array spectrophotometer.

In this report we describe an automated system that rapidly and automatically mixes reagents and records results, such as spectrophotometric changes. It employs a commercial diode array spectrophotometer and a novel dilution chamber in a flow stream that allows repetitive spectrophotometric rate measurements at accurately measured incremental substrate concentrations. When applied to enzyme kinetic studies, initial velocities at 15 different substrate or inhibitor concentrations, or pH values, can be recorded in a few minutes with high reproducibility, i.e., standard deviations less than 1%, and high sensitivity. Reactions occur in an 8-microliters flow cell and the reagent consumption is minimal. The concentration of incrementally diluted reagent in the cell is measured directly by means of an indicator dye added to the substrate. Michaelis-Menten parameters, inhibition constants, and pH profiles are determined for several enzymes including dehydrogenases producing NADH, a kinase requiring a coupled assay, and a hydrolase, carboxypeptidase A, in a reaction that produces a small decrease in absorbance.

Alcohol Dehydrogenase↗
PubMed1987

Pyruvate decarboxylase of Zymomonas mobilis: isolation, properties, and genetic expression in Escherichia coli.

Pyruvate decarboxylase (EC 4.1.1.1) from Zymomonas mobilis purified to homogeneity by using dye-ligand and ion-exchange chromatography. Antibodies produced against the enzyme and the amino-terminal sequence obtained for the pure enzyme were used to select and confirm the identity of a genomic clone encoding the enzyme selected from a genomic library of Z. mobilis DNA cloned into pUC9. The genomic fragment encoding the enzyme expressed high levels of pyruvate decarboxylase in Escherichia coli. Possible RNA polymerase and ribosome-binding sites have been identified in the 5'-untranslated region of the pyruvate decarboxylase gene.

Amino Acid Sequence↗
PubMed1986

Isolation and properties of the glycolytic enzymes from Zymomonas mobilis. The five enzymes from glyceraldehyde-3-phosphate dehydrogenase through to pyruvate kinase.

The five glycolytic enzymes glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, phosphoglycerate mutase, enolase and pyruvate kinase were each purified from extracts of Zymomonas mobilis cells, by using dye-ligand chromatography as the principal step. Two procedures, producing three and two of the enzymes respectively, are described in detail. Z. mobilis glyceraldehyde-phosphate dehydrogenase was found to be similar in most respects to the enzyme from other sources, except for having a slightly larger subunit size. Phosphoglycerate kinase has properties typical for this enzyme; however, it did not show the sulphate activation effects characteristic of this enzyme from most other sources. Phosphoglycerate mutase is a dimer, partially independent of 2,3-bisphosphoglycerate, and has a high specific activity. Enolase was found to be octameric; otherwise its properties were very similar to those of the yeast enzyme. Pyruvate kinase is unusual in being dimeric, and not requiring K+ for activity. It is not allosterically activated by sugar phosphates, having a high activity in the absence of any effectors. Some quantitative differences in the relative amounts of these enzymes, compared with eukaryotic species, are ascribed to the fact that Z. mobilis utilizes the Entner-Doudoroff pathway rather than the more common Embden-Meyerhoff glycolytic route.

Bacteria↗
PubMed1986

Strategies for enzyme isolation using dye-ligand and related adsorbents.

Approaches to the use of a large range of dye-ligand and similar adsorbents for protein isolation are described. The adsorbents behave in a similar fashion relative to each other with a variety of different applied protein mixtures, so a system of dividing the adsorbents into five groups according to their protein-binding ability has been adopted. In this way it becomes unnecessary to screen all dyes, and an ideal selection of dyes and conditions can quickly be achieved.

Adsorption↗
PubMed1986

The two alcohol dehydrogenases of Zymomonas mobilis. Purification by differential dye ligand chromatography, molecular characterisation and physiological roles.

The two alcohol dehydrogenases found in Zymomonas mobilis have each been purified using dye-ligand chromatography and affinity elution with nucleotides. The isoenzyme with lower electrophoretic mobility (ZADH-1) is a zinc enzyme with properties essentially similar to preparations described elsewhere. The faster isoenzyme (ZADH-2) accounted for some 90% of the ethanol-oxidizing activity in freshly prepared extracts and corresponded to the iron-activated enzyme previously described. This enzyme was inactivated by zinc; activity could only be retained during purification by including either ferrous ions or cobaltous ions in the buffers. ZADH-2 has relatively low acetaldehyde reductase activity; consequently ZADH-1 is responsible for about half of the physiological activity (acetaldehyde reduction) in Zymomonas cells. Kinetic studies showed that ZADH-2 is activated by ethanol in both reaction directions; a hypothesis for the mechanism of activation is presented. Metal ion analyses of ZADH-2 prepared in the presence of iron or cobalt indicated one atom of the relevant metal per subunit, with no significant zinc content. N-terminal sequence analyses showed that the ZADH-1 has some homology with the Bacillus stearothermophilus enzyme, whereas ZADH-2 resembles the yeast enzyme more closely.

Alcohol Dehydrogenase↗
PubMed1986

Glucose-fructose oxidoreductase, a new enzyme isolated from Zymomonas mobilis that is responsible for sorbitol production.

The enzymes responsible for sorbitol formation in Zymomonas mobilis were investigated. A previously undescribed enzyme catalyzes the intermolecular oxidation-reduction of glucose and fructose to form gluconolactone and sorbitol. This enzyme has been purified; it had a subunit size of 40,000 daltons and is probably tetrameric at low pH. It contained tightly bound NADP as the hydrogen carrier and did not require any added cofactor for activity. In addition, a gluconolactonase has been isolated, although not completely purified. Together these two enzymes were capable of completely converting a 54% (wt/vol) equimolar mixture of glucose and fructose to sorbitol and sodium gluconate at the optimum pH of close to 6.2. The oxidoreductase had low affinities for its substrates, but natural environmental conditions would expose it to high concentrations of sugars. The amount of the enzyme in Z. mobilis cells was sufficient to account for the rate of sorbitol formation in vivo. However, the enzyme was present in the highest amounts when the cells were grown on glucose alone, and it was repressed by the presence of fructose; this was not the case with the gluconolactonase.

Bacteria↗
PubMed1985

Simultaneous purification and characterization of glucokinase, fructokinase and glucose-6-phosphate dehydrogenase from Zymomonas mobilis.

The three enzymes glucokinase (EC 2.7.1.2), fructokinase (EC 2.7.1.4) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49) were isolated in high yield from extracts of Zymomonas mobilis. The principal steps in the isolation procedures involved the use of selected dye-ligand adsorbent columns, with affinity elution of two of the three enzymes. Glucokinase and fructokinase are dimeric proteins (2 X 33000 Da and 2 X 28000 Da respectively) and glucose-6-phosphate dehydrogenase is a tetramer (4 X 52000 Da). Some similarities in the structural and kinetic parameters of the two kinases were noted, but they have absolute specificity for their substrates. Fructokinase is strongly inhibited by glucose; otherwise non-substrate sugars had little effect on any of the three enzymes.

Adsorption↗
PubMed1985

Gluconate kinase from Zymomonas mobilis: isolation and characteristics.

The enzyme gluconate kinase EC 2.7.1.12 has been found at high levels in glucose-grown Zymomonas mobilis cells. A simple procedure, based on differential dye-ligand chromatography, has been used to isolate the enzyme, purifying it some 600-fold. The purified enzyme is a monomer of molecular weight 18,000 Da, which is much smaller than other gluconate kinases reported. It has a relatively low affinity for ATP. (Km = 1.5 mM), but high for gluconate (Km = 0.33 mM), and has little activity with any other potential substrates.

Chromatography↗
PubMed1984

Use of differential dye-ligand chromatography with affinity elution for enzyme purification: 2-keto-3-deoxy-6-phosphogluconate aldolase from Zymomonas mobilis.

2-Keto-3-deoxy-6-phosphogluconate aldolase (EC 4.1.2.14) has been isolated from extracts of Zymomonas mobilis using differential dye-ligand chromatography and affinity elution with product/product analog. The one-step procedure gives an enzyme with specific activity 600 units mg-1. Only 1 out of 47 dyes, Procion Yellow MX-GR, bound the enzyme completely in 20 mM phosphate buffer, pH 6.5. A column of Navy HE-R adsorbent was used first to remove most of the potentially adsorbing proteins.

Adsorption↗
PubMed1984

Use of differential dye-ligand chromatography with affinity elution for enzyme purification: 6-phosphogluconate dehydratase from Zymomonas mobilis.

Using differential dye-ligand chromatography and affinity elution with a substrate analog, 6-phosphogluconate dehydratase (EC 4.2.1.12) has been isolated from extracts of Zymomonas mobilis in a one-step procedure with 50% recovery. The specific activity of freshly isolated enzyme was 245 units mg-1. The enzyme contains iron, and it is rapidly inactivated in oxidizing conditions. It is inhibited by glycerophosphates, most strongly by the D-alpha-isomer which structurally corresponds to half of the substrate molecule.

Alkanesulfonates↗
PubMed1983

An iron-activated alcohol dehydrogenase.

An alcohol dehydrogenase isolated from Zymomonas mobilis was found to be activated by ferrous ions but not by zinc, after inactivation with metal-complexing agents. Cobaltous ions also re-activated to a lesser extent. It is suggested that in this species the alcohol dehydrogenase naturally contains iron. Kinetic studies on the iron-treated enzyme indicate an 'alcohol activation' phenomenon, which may have physiological relevance in overcoming product inhibition during fermentation.

Alcohol Oxidoreductases↗