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At least 253 records · Page 14Linked to original sources
PubMed1991

Removal of N-acetyl groups from blocked peptides with acylpeptide hydrolase. Stabilization of the enzyme and its application to protein sequencing.

Acylpeptide hydrolase, an enzyme that removes the modified residue from N-terminally acetylated peptides, has been purified from ovine liver and developed as a tool in sequencing blocked peptides and proteins. Its instability imposes a major limitation on the use of the mammalian enzyme in protein chemistry. Coupling to Sepharose followed by intramolecular cross-linking with dimethyl-suberimidate increased its thermostability and rendered it more resistant to inactivation by either SDS or N,N-dimethylformamide. The resulting enzyme preparation is reusable and more effective at cleaving longer acetylated peptides. It is therefore useful for unblocking acetylated proteins prior to protein sequence analysis. Intact proteins and many isolated peptides are still too large to be cleaved directly, but in this paper we describe a procedure for overcoming this difficulty. The protein is fragmented and non-acetylated peptides are then absorbed out with isothiocyanato-glass. The N-terminal peptide remains in solution and is unblocked with stabilised acylpeptide hydrolase. No chromatographic separation are required. The N-terminal sequence can then be obtained by automated Edman degradation. This procedure has been successfully demonstrated on a large synthetic peptide.

Amino Acid Sequence↗
PubMed1995

Increased thermal stability of the enzyme content in permeabilized whole cells from the fission yeast Schizosaccharomyces pombe by exogenous trehalose and other compounds.

Cells of the fission yeast Schizosaccharomyces pombe were permeabilized by treatment with toluene-ethanol. The permeabilized cells lost the bulk of the internal trehalose pool while most of the alkaline phosphatase, invertase, alpha-glucosidase, or neutral trehalase activities located inside the cells remained unaffected. This system was used as an in situ assay to determine the involvement of trehalose in enzyme protection during thermal treatments. The addition of trehalose to suspensions of permeabilized cells resulted in a sugar-dependent thermoprotection of the internal marker enzymes. This approach demonstrates that in whole cells of the fission yeast trehalose plays a physiological role as a protective molecule against thermal denaturation of cellular enzymes.

Alkaline Phosphatase↗
PubMed2006

Structure-based stabilization of an enzyme: the case of penicillin acylase from Alcaligenes faecalis.

The modeled structure of penicillin acylase from Alcaligenes faecali (AFPGA) was constructed by comparative modeling with the Modeller program. Candidate positions that could be replaced with cysteine were estimated by scanning the modeled structure of AFPGA with the program MODIP (modeling disulfide bond in protein). The mutant Q3C/P751C had a higher optimum temperature by three degrees than that of the wild type AFPGA. The half life of the double mutant Q3C/P751C at 55 degrees C was increased by 50%. To our knowledge, this was the first structure-based genetic modification of AFPGA.

Alcaligenes faecalis↗
PubMed1979

[Immobilization of enzymes on globulin].

Immobilization of lipase and amylosubtilisin on water-insoluble proteins, i. e. globulins, was studied. It was found that immobilization results in the enzyme stabilization. The immobilized enzyme can be transformed from the soluble state into the insoluble one and vice versa by changing the ionic strength of the solution. The advantages of immobilization on globulin in the reactions with water-insoluble substrates are demonstrated.

Enzymes, Immobilized↗
PubMed1984

Cloning of cDNA sequences for murine malic enzyme and the identification of aberrantly large malic enzyme mRNA in MOD-1 null mice.

Polysomes containing cytosolic malic enzyme mRNA and malic enzyme nascent chains were complexed with specific antibodies and purified by chromatography on protein A-Sepharose. When poly(A+) mRNA derived from the immunoselected polysomes was translated in vitro, full length malic enzyme (subunit Mr = 58,000) accounted for a significant fraction (approximately 20%) of the polypeptides synthesized. Double-stranded cDNA, synthesized using partially purified malic enzyme mRNA as a template, was inserted into pBR 322 and cloned. Twenty-five candidate malic enzyme cDNA clones were identified by differential hybridization. Four clones were studied further and each of these was shown to have malic enzyme cDNA sequences by hybrid-selected translation and specific immunoprecipitation. Plasmid pME1, which contains a 1400-base pair insert, hybridized to two mouse liver malic enzyme mRNAs with lengths of 2300 and 3500 bases. Similar analyses were performed on liver mRNAs isolated from MOD-1 mutant mice which lack cytosolic malic enzyme activity. These Northern blots disclosed a pair of aberrantly large malic enzyme mRNAs with lengths of 2800 and 4000 bases. Furthermore, anti-malic enzyme antibodies exclusively precipitated a polypeptide translation product with a Mr of 77,000 when MOD-1 mRNA was used to direct in vitro protein synthesis. Thus, it is possible that MOD-1 malic enzyme mRNA contains an additional polypeptide coding sequence. The translation of such a sequence might disrupt enzyme function and/or markedly decrease enzyme stability. The malic enzyme cDNA probe was also employed to demonstrate that the induction of malic enzyme in the livers of previously starved mice that were fed a high carbohydrate, fat-free diet was controlled pretranslationally by a parallel modulation of the malic enzyme mRNA concentration.

Animals↗
PubMed1993

Cloning and expression of Geotrichum candidum lipase II gene in yeast. Probing of the enzyme active site by site-directed mutagenesis.

The three-dimensional structure of lipase II of Geotrichum candidum strain ATCC34614 (GCL II) has provided insights with respect to the nature of the catalytic machinery of lipases. To support these structural observations, we have carried out an analysis of GCL II by mutagenesis. The gene encoding lipase II of Geotrichum candidum strain ATCC34614 (GCL II) was amplified using the polymerase chain reaction, cloned, and sequenced. The intronless lipase gene was expressed and secreted from Saccharomyces cerevisiae at approximately 5 mg/liter of culture. Recombinant GCL II was purified by immunoaffinity chromatography and characterized using a combination of substrates and independent analytical methods. The recombinant enzyme and the enzyme isolated from its natural source have comparable specific activities against triolein of about 1000 mumol of oleic acid released/min/mg of protein. The putative catalytic triad Ser217-His463-Glu354 was probed by site-directed mutagenesis. The substitution of Ser217 by either Cys or Thr and of His463 by Ala led to a complete elimination of the activity against both triolein and tributyrin. Substitution of Glu354 by either Ser, Ala or Gln renders the enzyme inactive and also perturbs the enzyme stability. However, the enzyme with the conservative replacement Glu354 Asp is stable and displays only a small decrease of triolein activity but a 10-fold decrease in activity against tributyrin. There was no appreciable difference in esterase activity between the native, recombinant wild type, and Glu354 Asp mutant. These results confirm that the triad formed by Ser217-Glu354-His463 is essential for catalytic activity. They also show that the active site of GCL II is more tolerant to a conservative change of the carboxylic side chain within the triad than are other hydrolases with similar catalytic triads.

Aspartic Acid↗
PubMed1995

Triglyceride hydrolysis and stability of a recombinant cutinase from Fusarium solani in AOT-iso-octane reversed micelles.

A recombinant cutinase from Fusarium solani was encapsulated in AOT reversed micelles. Physicochemical parameters of the system were optimized relative to triolein hydrolysis. Kinetic studies of triglyceride hydrolysis showed a decrease in specificity with increase of the acyl chain length. Stability of cutinase in the system under study is lower than in aqueous solution and decreases with increase in the water content in the system (W0 = [H2O]/[AOT]). The products of triolein hydrolysis had little effect on the cutinase stability. Although glycerol did not alter the stability, oleic acid decreases the enzyme stability. The increase in log P of solvent (from iso-octane to n-dodecane) decreased the stability. Deactivation profiles were fitted with the Henley and Sadana model (1).

Carboxylic Ester Hydrolases↗
PubMed1999

Combined effects of trehalose and cations on the thermal resistance of beta-galactosidase in freeze-dried systems.

The purpose of this study was to investigate the combined effects of trehalose and cations on the preservation of beta-galactosidase in freeze-dried systems and their relationship to physical properties. Differential scanning calorimetry was employed to measure the glass transition temperature (T(g)) and the endothermal peak area, related to the amount of crystalline trehalose dihydrate present in the samples. In systems in which the trehalose matrix was humidified to conditions which allowed a high proportion of trehalose to crystallize, the enzyme was rapidly inactivated upon heating at 70 degrees C. In these conditions the addition of CsCl, NaCl and particularly KCl or MgCl(2), improved the enzyme stability with respect to that observed in matrices containing only trehalose. For a given moisture content, addition of salts produced very little change on the glass transition temperature; therefore the protective effect could not be attributed to a higher T(g) value. The crystallization of trehalose dihydrate in the humidified samples was delayed in the trehalose/salt systems (principally in the presence of Mg(2+)) and a parallel improvement of enzyme stability was observed.

Calorimetry, Differential Scanning↗
PubMed2000

Extended stability of restriction enzymes at ambient temperatures.

The stability of restriction enzymes as supplied by manufacturers without any modification has been examined. No reduction in activity was observed for three enzymes (HindIII, EcoRI and Tsp509I) held at ambient temperature or 4 degrees C for the period of study (12 months), while activity was observed for up to 12 weeks after storage at 37 degrees C, which was considerably better than following desiccation with trehalose, a recognized preservation technique. A larger trial of 23 different restriction enzymes held at room temperature for one week showed that all enzymes retained significant activity. As a practical demonstration of the usefulness of this finding, enzymes were posted to Africa by conventional mail (cost $1 US) and shown to retain activity upon arrival after three weeks in transit (compared to a cost of $1000 US by cold-chain transportation). Supplying enzymes to third-world markets should now be possible by removing the necessity for cold-chain transport. After arrival, enzymes can simply be stored in a standard domestic refrigerator.

Cold Temperature↗
PubMed2005

Directed evolution of (betaalpha)(8)-barrel enzymes.

Natural molecular evolution supplies us with manifold examples of protein engineering. The imitation of these natural processes in the design of new enzymes has led to surprising and insightful results. Well-suited for design by evolutionary methods are enzymes with the common and versatile (betaalpha)(8)-barrel fold. Studies of enzyme stability, folding and design as well as the evolution of (betaalpha)(8)-barrel enzymes are discussed.

Animals↗
PubMed1985

Acute intermittent porphyria: characterization of a novel mutation in the structural gene for porphobilinogen deaminase. Demonstration of noncatalytic enzyme intermediates stabilized by bound substrate.

To investigate the molecular pathology in acute intermittent porphyria (AIP), the nature of the defective porphobilinogen (PBG)-deaminase was determined in erythrocyte lysates from 165 AIP heterozygotes from 92 unrelated families representing 20 different ethnic or demographic groups. Immunologic and physicokinetic studies revealed the occurrence of four classes of PBG-deaminase mutations. In the majority of families studied, the amount of immunoreactive enzyme protein corresponded to the amount of enzymatic activity, indicating the absence of cross-reacting immunologic material (CRIM) produced by the mutant allele. In 78 of these CRIM-negative families (designated type 1), the affected heterozygotes had half-normal PBG-deaminase activity. In three families (designated CRIM-negative type 2), symptomatic patients had increased urinary excretion of delta-aminolevulinic acid and PBG, and normal levels of erythrocyte PBG-deaminase activity. In contrast, noncatalytic, immunoreactive protein was expressed in heterozygotes from 11 families, about one-eighth of those studied, consistent with mutations in the structural gene for PBG-deaminase. Two types of CRIM-positive mutations were identified: the type 1 mutation had a CRIM/activity ratio of approximately 1.7 and a crossed-immunoelectrophoretic profile in which all the enzyme intermediates were increased, with the B or monopyrrole-enzyme intermediate predominant (B greater than A much greater than C congruent to D greater than E). The mutation altered both the kinetic and stability properties of the noncatalytic immunoreactive enzyme protein. The second CRIM-positive mutation, type 2, had markedly increased levels of noncatalytic immunoreactive protein (CRIM/activity ratio approximately 5.7). Crossed-immunoelectrophoresis revealed markedly increased amounts of the substrate-bound intermediates, B, C, D, and E (B greater than C greater than D greater than E much greater than A). The accumulation of these noncatalytic enzyme intermediates presumably resulted from the enhanced binding and/or defective release of substrate molecules. The conformation of these enzyme-substrate intermediates apparently rendered the complexes more resistant to intraerythrocyte proteolysis. These findings provide evidence for the presence of different allelic mutations in the structural gene for PBG-deaminase and document molecular genetic heterogeneity in AIP.

Acute Disease↗
PubMed1999

Utility of wiring nitrate reductase by alkylpyrroleviologen-based redox polymers for electrochemical biosensor and bioreactor applications.

The purpose of this work was to see if the alkylpyrroleviologen redox polymer technology previously developed for a reagentless nitrate biosensor based on nitrate reductase (NaR) from Escherichia coli (Cosnier, S.; Innocent, C.; Jouanneau, Y. Anal. Chem. 1994, 66, 3198-3201) could be applied to the isozyme from Aspergillus niger. In particular, the enzyme viability after immobilization was of great interest, as Cosnier et al. reported a residual activity of only 0.33% of the amount initially applied. The present work showed that A. niger NaR lost 99.2% of soluble activity on vacuum-drying in the presence of 2.5 nM N-methyl-N'-(12-[pyrrol-1-yl]dodecyl)-4,4'-bipyridinium ditetrafluoroborate monomer (C12V2+) and that most of this loss was due to monomer inhibition (91%). The loss due to dehydration was only 8%. In the biosensor configuration, the enzyme gave a residual activity of 0.18% of the amount originally applied and a specific response of 1.7 mA M-1 cm-2, but all activity was lost after 4 d storage at 4 degrees C in phosphate buffer. It was concluded that for practical biosensors and bioreactors, modification of the redox polymer format was needed, for example by covalent immobilization, to effect higher loading of viable NaR and improved enzyme stability.

Bioreactors↗
PubMed2002

Enzyme catalysis in ionic liquids.

Ionic liquids offer new possibilities for the application of solvent engineering to biocatalytic reactions. Although in many cases ionic liquids have simply been used to replace organic solvents, they have often led to improved process performance. Unlike conventional organic solvents, ionic liquids possess no vapor pressure, are able to dissolve many compounds, and can be used to form two-phase systems with many solvents. To date, reactions involving lipases have benefited most from the use of ionic liquids, but the use of ionic liquids with other enzymes and in whole-cell processes has also been described. In some cases, remarkable results with respect to yield, (enantio)selectivity or enzyme stability were observed.

Bacteria↗
PubMed2004

Optimization of Serratia marcescens lipase production for enantioselective hydrolysis of 3-phenylglycidic acid ester.

Lipase production and cell growth of Serratia marcescens ECU1010 were optimized in shake flasks, with lipase production being enhanced 9.5-fold (4,780 U/l) compared with the initial activity (500 U/l). Optimal carbon and nitrogen sources were Tween-80 and peptone, and the optimal ratio of Tween-80 to peptone was 1:3. The optimized cultivation conditions were 25 degrees C and pH 6.5. Lipase activity, particularly specific activity, could be improved by decreasing the cultivation temperature from 35 to 25 degrees C. Enzyme stability was significantly improved by simple immobilization with synthetic adsorption resin no. 8244. After five reaction cycles, enzyme activity decreased only very slightly, while enantioselectivity of the preparation remained constant, and the ees (enantiomeric excess of the remaining substrate) achieved in all cases was higher than 97%. The resin-8244-lipase preparation can be used for efficient enantioselective hydrolysis of trans-3-(4'-methoxyphenyl)glycidic acid methyl ester [(+/-)-MPGM], a key intermediate in the synthesis of Diltiazem.

Enzyme Stability↗
PubMed1988

Human skin tryptase: purification, partial characterization and comparison with human lung tryptase.

Human skin tryptase was isolated using stepwise low- and high-salt extraction and further purified 448-fold with 33% yield using octyl-Sepharose CL-4B hydrophobic affinity chromatography, Sephacryl S-200 gel filtration and finally octyl-Sepharose CL-4B or cellulose phosphate ion exchange chromatography. The skin tryptase, which has an apparent Mr of 120,000 by gel filtration in high-salt buffer, consisted of polypeptide chains of Mr 34,000 and 38,000 when resolved on SDS gels. Both polypeptide chains, labelled with [3H]diisopropyl fluorophosphate, indicated that they were representative of subunits and that the native proteinase was an aggregate of subunits. However, in some preparations only one band with Mr 34,000 was seen. In low-salt buffer the enzyme was labile and at least 1.4 M KCl was needed to keep the enzyme stabile when incubated at 37 degrees C for 30 min. Heparin glycosaminoglycan partially stabilized the tryptase but addition of protein (e.g. albumin, 80 micrograms/ml) to the tryptase-heparin mixture was needed to keep the enzyme stabile. Tryptases purified by exactly the same method from human lung tissue and from human skin had identical molecular size in gel filtration and in SDS-polyacrylamide gel electrophoresis. They also revealed identical enzyme kinetic parameters with several synthetic peptide substrates. The inhibition profile was identical for both enzymes, and they also crossreacted completely in immunodiffusion plates. These studies strongly indicate that mast cells found in skin as well as lung contain closely related, possible identical trypsin-like proteinases.

Chromatography, Gel↗