Properties and function of malate enzyme from Pseudomonas putida

Malate enzyme (L-malate: NADP+ oxidoreductase (oxalacetate-decarboxylating, EC 1.1.1.40)) has been purified from Pseudomonas putida to 99 per cent homogeneity by heat, ammonium suphate fractionation, gel filtration and anion exchange chromatography. Sodium dodecylsulphate-(SDS)-polyacrylamide disc gel electrophoresis analysis showed an approximate tetrameric subunit with a molecular weight of 52,000. The purified enzyme showed a pH optimum between 8.0 and 8.5 (for Tris-HCl buffer) and required bivalent cations for catalysis; monovalent ions like K+ and NH4+ acted as very effective activators. The temperature-activity relationship for the malate enzyme from 35-80 degrees C showed broken Arrhenius plots with an inflexion at 65 degrees C. The enzyme halflife was 30s at 85 degrees C. The enzyme showed hyperbolic kinetics for both substrates with apparent Km values of 4.0 X 10(-4) M and 2.3 X 10(-5) M for L-malate and NADP+ respectively. From the study of the effects of some compounds on the enzyme, the physiological significance of those produced by fumarate, succinate and oxalacetate can be emphasized.     

Properties of 1-phosphofructokinase from Pseudomonas putida.

The 1-phosphofructokinase (1-PFK, EC 2.7.1.56) from Pseudomonas putida was partially purified by a combination of (NH4)2SO4 fractionation and DEAE-Sephadex column chromatography. In its kinetic properties, this enzyme resembled the 1-PFK's from other bacteria. With the substrates fructose-1-phosphate (F-1-P) and adenosine triphosphate (ATP) Michaelis-Menten kinetics were observed, the Km for one substrate being unaffected by a variation in the concentration of the other substrate. At pH 8.0, the Km values for F-1-P and ATP were 1.64 X 10(-4) M and 4.08 X 10(-4) M, respectively. At fixed concentrations of F-1-P and ATP, an increase in the Mg2+ resulted in sigmoidal kinetics. Activity was inhibited by ATP when the ratio of ATP:Mg2+ was greater than 0.5 suggesting that ATP:2 Mg2+ was the substrate and free ATP was inhibitory. Activity of 1-PFK was stimulated by K+ and to a lesser extent by NH4+ and Na+. The reaction rate was unaffected by 2 mM K2HPO4, pyruvate, phosphoenolpyruvate, adenosine monophosphate, adenosine 3',5'-cyclic monophosphate, fructose-6-phosphate, glucose-6-phosphate, 6-phosphogluconate, 2-keto-3-deoxy-6-phosphogluconate, or citrate. The results indicated that the 1-PFK from P. putida was not allosterically regulated by a number of metabolites which may play an important role in the catabolism of D-fructose.     

Properties and functions of two succinic-semialdehyde dehydrogenases from Pseudomonas putida

Two forms of succinic-semialdehyde dehydrogenase have been isolated in Pseudomonas putida. The two enzymes could be separated by filtration on Sephacryl S-300 and their apparent molecular weights were approx. 200,000 and 100,000. The smaller enzyme, which is induced by growth on 4-hydroxyphenylacetate, has been purified to 88% homogeneity by anion-exchange and affinity chromatography. Electrophoresis in sodium dodecyl sulphate gave rise to a molecular weight of 53,000, indicating that the native enzyme is dimeric. Under standard assay conditions this enzyme acts preferentially with NAD but reduces NADP at 9% of the rate observed for NAD. The large enzyme, which is dependent on NADP, is induced by growth on putrescine and its induction is highly coordinated with putrescine: 2-oxoglutarate transaminase, gamma-amino-butyraldehyde dehydrogenase and gamma-aminobutyrate: 2-oxoglutarate transaminase activities. Activity and stability conditions and true Km values for substrate and cosubstrates of the two enzymes were determined.     

Crystallization and properties of L-arginine deiminase of Pseudomonas putida.

Crystalline L-arginine deiminase of Pseudomonas putida was prepared by the following steps: sonic disruption, ammonium sulfate fractionation, protamine sulfate treatment, DEAE-cellulose column chromatography, and L-arginine-Sepharose 6B chromatography followed by crystallization. This procedure yields a crystalline pure enzyme with a 45% recovery of the activity in crude cell-free extracts. The yield is significantly higher than that reported for this enzyme. The purified enzyme appears to be homogeneous in ultracentrifugation (s-o20, w equals 10.2 S) and isoelectric focusing (pI equals 6.13). The purified enzyme showed two bands on disc gel electrophoresis, both carrying out the deimination of L-arginine. Electrophoresis in the presence of beta-mercaptoethanol plus Na dodecyl-SO4 gave a single band (Mr, 54,000). Specific activity of this enzyme was 58.8 mumol of L-citrulline formed per min per mg of protein at 37 degrees. The optimum pH of the purified enzyme was 6.0 and maximal activity was obtained at 50 degrees. The molecular weight of the native protein was 130,000 by gel filtration and 120,000 by sedimentation-equilibrium measurements. The spectrum of the pure enzyme showed absorption maximum at 280 nm and the value of E-1%-1 CM AT 280 NM WAS 10.48 IN 0.05 M potassium phosphate buffer (pH 7.0). The crystalline enzyme hydrolyzed several L-arginine analogues. L-Homoarginine, L-alpha-amino-gamma-guanidinobutyric acid, and L-alpha-amino-beta-guanidinopropionic acid competitively inhibited the hydrolysis of L-arginine with Ki values of 25.7, 7.5, and 4.0 times 10- minus 3 M, respectively. p-Chloromercuribenzoate, Ag-+, and Hg-2+, and several metal ions inhibited the enzyme.     

Sarcosine Dehydrogenase from Pseudomonas putida: Purification and Some Properties

A sarcosine dehydrogenase was purified to homogeneity from cell free extract of Pseudomonas putida aerobically grown in a medium containing creatinine or betaine as the carbon and nitrogen sources. The enzyme catalyzed dehydrogenation of N-methyl derivatives of some amino acids but was inert toward dimethylglycine, betaine and choline. Phenazine methosulfate, 2, 6-dichlorophenol indophenol, methylene blue, meldora blue, nile blue and potassium ferricyanide served as electron carriers. The maximal activity was observed at pH 8.0–9.0. The Km and K_max values for sarcosine were 29 mm and 1.2 μmol/min/mg, respectively. The molecular weight was estimated to be about 170,000, presumably composed of four sub-units. Spectrophotometric and fluorometric analyses indicated that the enzyme was a flavoprotein.     

Purification and Properties of 2-Halo Acid Dehalogenase from Pseudomonas putida

Previous studies of potato varieties indicated that changes during cooking could be mathematically described and that some chemical components and the cell size may influence the cooking behavior. To find out whether the same principles can be adopted for other root vegetables, the cooking behavior of three other low-starch root vegetables were investigated and the results compared. Slices (6 mm thick and 30 mm diameter) were treated in water at 100°C. Mathematical expressions were assessed, and coefficients were determined to describe the kinetic behavior of the products. The cell size and pectin content of the raw materials determined the cooking characteristics. Texture development could be predicted by shear force measurements.     

Chromate-Reducing Properties of Soluble Flavoproteins from Pseudomonas putida and Escherichia coli

Cr(VI) (chromate) is a toxic, soluble environmental contaminant. Bacteria can reduce chromate to the insoluble and less toxic Cr(III), and thus chromate bioremediation is of interest. Genetic and protein engineering of suitable enzymes can improve bacterial bioremediation. Many bacterial enzymes catalyze one-electron reduction of chromate, generating Cr(V), which redox cycles, generating excessive reactive oxygen species (ROS). Such enzymes are not appropriate for bioremediation, as they harm the bacteria and their primary end product is not Cr(III). In this work, the chromate reductase activities of two electrophoretically pure soluble bacterial flavoproteins—ChrR (from Pseudomonas putida) and YieF (from Escherichia coli)—were examined. Both are dimers and reduce chromate efficiently to Cr(III) (k_cat/K_m = ~2 × 10⁴ M⁻¹·s⁻¹). The ChrR dimer generated a flavin semiquinone during chromate reduction and transferred >25% of the NADH electrons to ROS. However, the semiquinone was formed transiently and ROS diminished with time. Thus, ChrR probably generates Cr(V), but only transiently. Studies with mutants showed that ChrR protects against chromate toxicity; this is possibly because it preempts chromate reduction by the cellular one-electron reducers, thereby minimizing ROS generation. ChrR is thus a suitable enzyme for further studies. During chromate reduction by YieF, no flavin semiquinone was generated and only 25% of the NADH electrons were transferred to ROS. The YieF dimer may therefore be an obligatory four-electron chromate reducer which in one step transfers three electrons to chromate and one to molecular oxygen. As a mutant lacking this enzyme could not be obtained, the role of YieF in chromate protection could not be directly explored. The results nevertheless suggest that YieF may be an even more suitable candidate for further studies than ChrR.     

Crystallization and preliminary X-ray crystallographic studies of ketosteroid isomerase from Pseudomonas putida biotype B

The Δ⁵-3-ketosteroid isomerase from Pseudomonas putida biotype B has been crystallized. The crystals belong to the space group P2₁2₁2₁ with unit cell dimensions of a = 36.48 Å, b = 74.30 Å, c = 96.02 Å, and contain one homodimer per asymmetric unit. Native diffraction data to 2.19 Å resolution have been obtained from one crystal at room temperature indicating that the crystals are quite suitable for structure determination by multiple isomorphous replacement.     

Crystallization and Properties of Amine Dehydrogenase from Pseudomonas sp.

An amine dehydrogenase was purified and crystallized from the cell free extract of a Pseudomonas sp., isolated from soil by means of the enrichment technique. The crystalline enzyme gave a single band on polyacrylamide gel electrophoresis and the molecular weight of the enzyme was estimated to be 100,000 by gel filtration on a Sephadex column. Upon SDS-gel electrophoresis, the enzyme was dissociated into two nonidentical subunits having molecular weights of 60,000 (dehydrogenase) and 39,000 (cytochrome c). The absorption spectrum of the enzyme showed absorption maxima at 550 nm, 524 nm, 411 nm and 280 nm, and a broad shoulder at around 350 nm, indicating that the enzyme was purified as a dehydrogenase-cytochrome c complex. The prosthetic group of the dehydrogenase was identified as covalently bound pyrroloquinoline quinone. The enzyme showed a broad substrate specificity toward various amines including aliphatic monoamines, aliphatic diamines, aromatic amines and polyamines.     

Metal-characterization of N-Acyl-D-glutamate Amidohydrolase from Pseudomonas sp. Strain 5f-l

N-Acyl-D-glutamate amidohydrolase (D-AGase) from Pseudomonas sp. 5f-1 was a zinc-metalloenzyme which contained 2.06–2.61 g. atom of Zn per mole of enzyme. The zinc atom was required for the catalytic activity and stability of the enzyme. The N-terminal amino acid sequence of Pseudomonas sp. 5f-l D-AGase showed 32% identity to that of Alcaligenes xylosoxydans subsp. xylosoxydans A-6.     

Purification and characterization of adhesive exopolysaccharides from Pseudomonas putida and Pseudomonas fluorescens

In this study, the adhesive exopolysaccharides of strains of Pseudomonas putida and P. fluorescens, both isolated from freshwater epilithic communities, were examined with regard to their chemical composition, biosynthesis, and their role in adhesion. Electron microscopy showed that both strains were enrobed in fibrous glycocalyces and that these structures were involved in attachment of the cells to a solid surface and as structural matrices in the microcolony mode of growth. In batch culture experiments most of the extracellular polysaccharide of both strains was found to be soluble in the growth medium rather than being associated with bacterial cells. Exopolysaccharide was synthesized during all phases of growth, but when growth was limited by exhaustion of the carbon source, exopolysaccharide synthesis ceased whereas exopolysaccharide synthesis continued for some time after cessation of growth in nitrogen-limited cultures. Exopolysaccharide from both strains was isolated and purified. Pseudomonas putida synthesized an exopolysaccharide composed of glucose, galactose, and pyruvate in a ratio of 1:1:1; the P. fluorescens polymer contained glucose, galactose, and pyruvate in a ratio of 1:1:0.5, respectively. Polymers from both strains were acetylated to a variable degree.     

Characterization and Two-Dimensional Crystallization of Membrane Component AlkB of the Medium-Chain Alkane Hydroxylase System from Pseudomonas putida GPo1

The alkane hydroxylase system of Pseudomonas putida GPo1 allows it to use alkanes as the sole source of carbon and energy. Bacterial alkane hydroxylases have tremendous potential as biocatalysts for the stereo- and regioselective transformation of a wide range of chemically inert unreactive alkanes into valuable reactive chemical precursors. We have produced and characterized the first 2-dimensional crystals of the integral membrane component of the P. putida alkane hydroxylase system, the nonheme di-iron alkane monooxygenase AlkB. Our analysis reveals for the first time that AlkB reconstituted into a lipid bilayer forms trimers. Addition of detergents that do not disrupt the AlkB oligomeric state (decyl maltose neopentyl glycol [DMNG], lauryl maltose neopentyl glycol [LMNG], and octaethylene glycol monododecyl ether [C₁₂E₈]) preserved its activity at a level close to that of the detergent-free control sample. In contrast, the monomeric form of AlkB produced by purification in n-decyl-β-d-maltopyranoside (DM), n-dodecyl-β-d-maltopyranoside (DDM), octyl glucose neopentyl glycol (OGNG), and n-dodecyl-N,N-dimethylamine-N-oxide (LDAO) was largely inactive. This is the first indication that the physiologically active form of membrane-embedded AlkB may be a multimer. We present for the first time experimental evidence that 1-octyne acts as a mechanism-based inhibitor of AlkB. Therefore, despite the lack of any significant full-length sequence similarity with members of other monooxygenase classes that catalyze the terminal oxidation of alkanes, AlkB is likely to share a similar catalytic mechanism.     

Properties of the inducible hydroxyproline transport system of Pseudomonas putida

Features of the transport system for hydroxyproline in a strain of Pseudomonas putida were studied. A mutant, lacking hydroxyproline-2 epimerase and unable to metabolize hydroxy-l-proline, was shown to transport and accumulate this compound after induction. Both entry and exit rates were examined, and kinetic constants for the reaction were determined. Increasing the induction time from 0.5 to 3 hr increased the entry rate three- to fourfold but had only a small and variable effect on the exit rate. Entry followed saturation kinetics. For hydroxy-l-proline, the K(m) and V(max) values were found to be 3 x 10(-5)m and 6 mumoles per g (dry weight) per min, respectively. The K(m) and V(max) for the epimer allohydroxy-d-proline were 10(-3)m and 0.1 mumole per g (dry weight) per min. Entry rates into "loaded" and "unloaded" cells were found to be the same. Exit was shown to be first order over the range of internal substrate concentrations measured. Exit rates were measured by several different methods and found to be independent of external substrate concentration. The first-order exit rate constant was computed to be 0.23 min(-1). Several metabolic inhibitors were examined for their effect on transport. The inhibitory action of N-ethyl maleimide was shown to be greatly reduced if cells were allowed to accumulate hydroxy-l-proline before exposure to the inhibitor. A number of other amino acids interfered with the transport of hydroxy-l-proline; the greatest effect was produced by l-alanine and l-proline.     

Properties of the iron--sulphur proteins of the benzene dioxygenase system from Pseudomonas putida.

A purification procedure was developed to stabilize the iron-sulphur proteins of the benzene dioxygenase system from Pseudomonas putida. The intermediate electron-carrying protein has a mol. wt. of 12300 and possesses one (2Fe--2S) cluster, whereas the terminal dioxygenase has a mol.wt. of 215300 and possesses two (2Fe--2S) clusters. The order and stoicheiometry of electron transfer and of the whole system are described.