Ein neues Verfahren zum direkten Nachweis mikrobieller Aminoacylaseaktivität auf Agarplatten mit o-Phthalaldehyd / A New Detection Procedure for Aminoacylase Activity of Microorganisms Directly on Plate Culture with o-Phthalaldehyde

Not less than 1 nmol of methionine and phenylalanine were detected as fluorescent spots on agar plates with ophthalaldehyde reagent under UV light. Microorganisms were grown on thin- agar-layer coated filter papers placed on nutrient agar plates, and then transfered onto new plates lacking nutrients by moving the papers. After the background amino compounds were removed by the diffusion to the bottom plates, the paper cultures were moved and incubated on assay plates containing N-acetylmethionine or N-acetylphenylalanine. The amino acids formed around the colonies were visualized by the ophthalaldehyde procedure to indicate aminoacylase activity of microorganisms. The substrate- and stereospecificity of the enzyme was shown for some strains on the agar plates by this procedure.

Nagra/PSI Chemical Thermodynamic Data Base 01/01

The Nagra/PSI Chemical Thermodynamic Data Base has been updated to support performance assessments of the planned Swiss repositories for radioactive waste. The update from version 05/92 to 01/01 involved major revisions for most of the actinides and fission products. Altogether, more than 70% of the database contents have been revised. Data for U, Np, Pu, Am and Tc recommended by the NEA TDB project were considered in the update. Thermodynamic data for Th, Sn, Eu, Pd, Al, and solubility and metal complexation of sulphides and silicates were extensively reviewed. Data for Zr, Ni and Se were examined less rigorously as these elements are currently being reviewed in phase II of the NEA TDB project. Our experiences from this two year team effort can be summarised as follows. Detailed in-house reviews and critical appraisal of NEA recommendations greatly improved the chemical consistency and quality of the selected data. On the other hand, we could discern major gaps in the data, especially missing carbonate complexes. In some systems,e.g. Th(IV)-H2O and U(IV)-H2O, experimental data could not be described by a unique set of thermodynamic constants. There, a pragmatic approach based on solubility data was chosen for application to performance assessment. The electronic version of our database and information concerning its full documentation is available on our PSI web site (http://www.psi.ch/les).

Synthesis of enantiopure (5R)-hydroxyhexane-2-one with immobilised whole cells of Lactobacillus kefiri

Whole-cell reduction of (2,5)-hexanedione to yield highly enantiopure (5R)-hydroxyhexane-2-one (enantiomeric excess >99%) with Lactobacillus kefiri DSM 20587 was investigated. Cell immobilisation with sodium cellulose sulphate was chosen as the most suitable encapsulation matrix, giving an immobilisation yield of 40%. Despite the lowered biocatalytic activity from cell immobilisation, the bioreduction process was vastly improved with the help of reaction engineering techniques (batch to a plug flow reactor set-up). High selectivity (95%) and space-time yield (87 g L(-1) day(-1)) were achieved in the plug flow reactor. The biocatalyst remained active (68% residual activity) after 6 days of operation.

Cloning, sequence analysis, and heterologous expression of the gene encoding a (S)-specific alcohol dehydrogenase from Rhodococcus erythropolis DSM 43297

The gene encoding an (S)-specific NAD-dependent alcohol dehydrogenase (RE-ADH) was isolated from the genomic DNA of Rhodococcus erythropolis DSM 43297. The nucleotide sequence of 1,047 bp, coding for 348 amino acids, was cloned in Escherichia coli cells and successfully expressed. The subunit molecular mass as deduced from the amino acid sequence was determined to be 36.026 kDa. The recombinant enzyme exhibited high thermostability, which facilitated its purification by heat treatment, followed by two column-chromatography steps. RE-ADH shows high similarity to several zinc-containing medium-chain alcohol dehydrogenases. All zinc ligands seem to be conserved except one of the catalytic zinc ligands, where Cys is probably substituted by Asp. A similarity of 84% with a phenylacetaldehyde reductase from Corynebacterium sp. ST-10 was determined. Biochemical properties such as thermostability and substrate specificity of the two enzymes were compared.

Diastereoselective synthesis of optically active (2 R,5 R)-hexanediol

Diastereoselective reduction of diketones with Lactobacillus kefir DSM 20587 was examined. The reduction of both oxo-functions proceeded highly diastereoselectively. (2 R,5 R)-Hexanediol 3 was produced starting from (2,5)-hexanedione 1 in quantitative yields with enantiomeric excess >99% and diastereomeric excess >99%. The reaction conditions were optimized: maximum yield of (2 R,5 R)-hexanediol was reached at pH 6, 30 degrees C and with equal amounts of substrate and cosubstrate. The applicability of the system in fed-batch experiments was demonstrated. The feed specific biomass concentration required to reach maximal yield and selectivity in fed-batch mode was determined.

Biocatalytic reduction of beta,delta-diketo esters: a highly stereoselective approach to all four stereoisomers of a chlorinated beta,delta-dihydroxy hexanoate

A stereoselective chemoenzymatic synthesis of all four stereoisomers of tert-butyl 6-chloro-3,5-dihydroxy-hexanoate (6a) is presented. The key step of the sequence is a highly regio- and enantioselective single-site reduction of tert-butyl 6-chloro-3,5-dioxohexanoate (1a) by two enantiocomplementary biocatalysts. Alcohol dehydrogenase from Lactobacillus brevis (recLBADH) afforded a 72% yield of enantiopure tert-butyl (S)-6-chloro-5-hydroxy-3-oxohexanoate [(S)-2a]. The enantiomer (R)-2a was prepared with 90-94% ee by Baker's yeast reduction in a biphasic system (50% yield). Both biotransformations were performed on a gram scale. The beta-keto group of the enantiomeric delta-hydroxy-beta-keto esters 2a thus obtained was reduced by syn- and anti-selective borohydride reductions. Permutation of the reduction methods yielded all four stereoisomers of the crystalline target compound 6a (> or = 99.3% ee, dr > or = 205:1), which is a versatile 1,3-diol building block. recLBADH accepts a variety of beta,delta-diketo esters as was determined in a photometric assay. tert-Butyl 3,5-dioxo-hexanoate (1b) and tert-butyl 3,5-dioxo-heptanoate (1c) were reduced on a preparative scale as well to afford the corresponding delta-hydroxy-beta-keto esters (R)-2b and (R)-2c with 99.4% ee and 98.1% ee, respectively.

Sorption behaviour of Am on marl groundwater colloids

The sorption of americium on marl colloids is studied in a comprehensive way. In Na-HCO3 groundwater conditions, americium in the concentration range 3 x 10(-11)-3 x 10(10) M sorbs onto groundwater colloids. In these tests, the colloid concentration is rather high, i.e. Ccoll 1.7+/-1.3 mg l(-1) for sizes 505000 nm or Ncoll (1.7+/-0.1) x 10(11) l(-1) for sizes larger than 100 nm. These colloids are mainly chlorite and smectite/illite with an average size smaller than 500 nm. For the groundwater (pH 8.6, [Na+]-[HCO3]-2 x 10(-2) M), Kd values in the range 1-3 x 10(6)mlg(-1) are measured. These values are compared with experimental and modelled values reported earlier in the literature.

Crystallization and preliminary characterization of crystals of R-alcohol dehydrogenase from Lactobacillus brevis

The R-specific alcohol dehydrogenase (RADH) from Lactobacillus brevis is a valuable catalyst for the production of chiral alcohols that can be used as synthons in asymmetric syntheses. RADH is a homotetramer with 222 symmetry and a molecular mass of 107 kDa. The recombinant enzyme has been expressed in Escherichia coli, purified to homogeneity and crystallized. The crystals belong to the orthorhombic space group I222, with unit-cell parameters a = 56.5, b = 85.1, c = 115.4 A, and diffract X-rays to at least 1.8 A resolution. The calculated crystal packing parameter V(M) = 2.59 A(3) Da(-1), corresponding to a solvent content of 52.5% and suggesting that one RADH monomer is contained in the asymmetric unit. The RADH tetramer lies on a special position with its molecular dyads coinciding with the crystallographic twofold axes and with its centre of mass on the origin of the unit cell.

Sex differences in 'climacteric symptoms' with increasing age? A hypothesis-generating analysis of cross-sectional population surveys

Are the established clinical symptoms of the female climacteric really specific for women? We were interested to compare the prevalence of these symptoms across age and sex. In the absence of longitudinal (cohort) studies, we tried to find cross-sectional, population-based studies with a broad age span to find a preliminary answer. We obtained six surveys that contained information for at least some of the symptoms. We re-analyzed these databases, which included over 8000 males and 8000 females, in a pooled fashion. Sixteen symptoms of predominantly somatic, psychological and urogenital origin were identified and the age-dependent increase of the relative frequencies was compared between genders. A general tendency for women to report more symptoms was confirmed; however, no significant differences were found between genders regarding the time trend of these symptoms. The analyses suggest that males experience a similar symptomatology in the same age span as women. One may thus be tempted to conclude that aging males experience similar phenomena to women during their menopausal transition. This should be confirmed in a specifically designed study.

Large-scale applications of NAD(P)-dependent oxidoreductases: recent developments

NAD(P)-dependent dehydrogenases are useful catalysts for the synthesis of chiral compounds. Many active and stable enzymes are available that (with high enantioselectivity) reduce ketones or keto acids to chiral alcohols, hydroxy acids or amino acids. For economic reasons, these reactions need coupling to the simultaneous regeneration of NAD(P)H. For preparative applications, three components have to be combined: an appropriate enzyme, an efficient coenzyme-regenerating step and a suitable reaction-engineering technique.

Screening and characterization of new enzymes for biosensing and analytics

The development of new or improved analytical methods requires new enzymes. Screening techniques utilizing enrichment cultures and rapid assay methods supported by automated or miniaturized methods are useful tools to detect new enzyme producers. Notably, oxidoreductases are well suited for analytical purposes. The NAD(P)- and oxygen-independent quinoprotein dehydrogenases with a covalently bound redox cofactor can be used advantageously for the development of biosensors. Examples are given of selective enrichment methods used in screening for useful enzyme-producing microorganisms. Enrichment under chemostatic conditions proved to be successful because enzymes with a remarkably high affinity against the analyte could be obtained. This is demonstrated by the screening of a trimethylamine-converting enzyme. The frequently observed high selectivity of these enzymes against the substrate is demonstrated in a few examples. In exploitation of these new oxidoreductases, new analytical methods were developed which are useful for the detection and during monitoring of phenylketonuria (PKU) or maple syrup urine disease (MSUD).

New alcohol dehydrogenases for the synthesis of chiral compounds

The enantioselective reduction of carbonyl groups is of interest for the production of various chiral compounds such as hydroxy acids, amino acids, hydroxy esters, or alcohols. Such products have high economic value and are most interesting as additives for food and feed or as building blocks for organic synthesis. Enzymatic reactions or biotransformations with whole cells (growing or resting) for this purpose are described. Although conversions with whole cells are advantageous with respect to saving expensive isolation of the desired enzymes, the products often lack high enantiomeric excess and the process results in low time-space-yield. For the synthesis of chiral alcohols, only lab-scale syntheses with commercially available alcohol dehydrogenases have been described yet. However, most of these enzymes are of limited use for technical applications because they lack substrate specificity, stability (yeast ADH) or enantioselectivity (Thermoanaerobium brockii ADH). Furthermore, all enzymes so far described are forming (S)-alcohols. Quite recently, we found and characterized several new bacterial alcohol dehydrogenases, which are suited for the preparation of chiral alcohols as well as for hydroxy esters in technical scale. Remarkably, of all these novel ADHs the (R)-specific enzymes were found in strains of the genus Lactobacillus. Meanwhile, these new enzymes were characterized extensively. Protein data (amino acid sequence, bound cations) confirm that these catalysts are novel enzymes. (R)-specific as well as (S)-specific ADHs accept a broad variety of ketones and ketoesters as substrates. The applicability of alcohol dehydrogenases for chiral syntheses as an example for the technical use of coenzyme-dependent enzymes is demonstrated and discussed in this contribution. In particular NAD-dependent enzymes coupled with the coenzyme regeneration by formate dehydrogenase proved to be economically feasible for the production of fine chemicals.

Enzymatic method for determination of branched-chain amino acid aminotransferase activity

A spectrophotometric assay for the determination of branched-chain L-amino acid aminotransferase activity is described. It is based on the transamination of L-leucine in the presence of 2-oxoglutarate yielding 4-methyl-2-oxopentanoate. The rate of formation of the branched-chain 2-oxo acid is specifically monitored in a coupled enzymatic reaction using NAD(+)-dependent D-2-hydroxyisocaproate dehydrogenase from Lactobacillus casei ssp. pseudoplantarum as coupling enzyme by measuring the decrease in NADH absorbance at 334 nm. Optimized assay conditions are provided as evaluated for the (iso)enzyme from rat heart.

Neonatal screening for maple syrup urine disease by an enzyme-mediated colorimetric method

A microplate-based, enzyme-mediated, colorimetric method using L-leucine dehydrogenase (EC 1.4.1.9) has been developed for the determination of the combined branched-chain amino acids in plasma and blood-spot specimens. The test exhibits acceptable precision and fits into a new concept according to which the different parameters of neonatal screening programs for metabolic disorders, such as phenylalanine (phenylketonuria), galactose/galactose-1-phosphate (galactosemia) and branched-chain amino acids (maple syrup urine disease) can be measured in the same blood-spot eluate by use of different specific NAD(H)-dependent enzymes.

Determination of (S)- and (R)-2-oxo-3-methylvaleric acid in plasma of patients with maple syrup urine disease

An enzymatic method for the separate measurement of both chiral 2-oxo-3-methylvaleric acid (OMV) compounds, (S)- and (R)-OMV, by NADH-dependent enantioselective amination using leucine dehydrogenase in the presence of a NADH regenerating system is described. This method allows the quantitative determination of all branched-chain 2-oxo acids, simultaneously. In plasma samples from classical maple syrup urine disease patients under therapy the average (R)-OMV/(S)-OMV ratio was 0.35 and great differences in the transamination equilibria of the diastereomeric branched-chain amino acids L-isoleucine and L-alloisoleucine were demonstrated.

[Collection and processing of ophthalmologic findings with a personal computer]

In a recently presented paper we proved that it is easy possible to store and analyse data form patients in a strabological department by using purchable data base programs and personal computers. The new program, we now use, has the opportunity to show all inputs in a special data field (i.e. the diagnosis field) in alphabetical order on the screen. For standardization in the data file we have created a special record. In all fields all possible and allowed inputs are entered. When entering new data of a patient, the user only has to select and to transfer the data from one field into the other. This has three advantages: 1. Time is saved when entering data, because it is not necessary to encode the data in an alphanumerical code. 2. The presentation of the data on the monitor is easy understandable. 3. It is not possible to enter no standardized data.

A new approach to the newborn screening for hyperphenylalaninemias: use of L-phenylalanine dehydrogenase and microtiter plates

We adapted the recently described colorimetric method for the specific determination of phenylalanine to a microplate assay using a NAD(H)-dependent L-phenylalanine dehydrogenase. With respect to sensitivity, analytical recovery and interrun imprecision this method for measuring phenylalanine in eluates of paper-dried blood spots is suitable for routine newborn screening for hyperphenylalaninemias. In contrast to the microbiological Guthrie assay, with the enzymatic method quantitative data may be obtained on the same day, also in the blood of newborns on antibiotic treatment.

PEANUT: computer graphics program to represent atomic displacement parameters

PEANUT is an easy to use computer graphics program for the visualization and real-time manipulation of the atomic displacement parameters of small molecules. A flexible, dynamic data structure allows the user to compute complicated, nonspherical atomic surfaces and to handle the point group symmetry of the molecules automatically. Pictures with hidden-line removal may be plotted in publication quality on appropriate output devices.

A convenient enzymatic method for the determination of 4-methyl-2-oxopentanoate in plasma: comparison with high performance liquid chromatographic analysis

A simple and rapid spectrophotometric method for the estimation of 4-methyl-2-oxopentanoate in plasma samples by use of NAD+-dependent D-2-hydroxyisocaproate dehydrogenase from Lactobacillus casei ssp. pseudoplantarum is described. It is based on the kinetic measurement of the decrease of NADH absorbance at 334 nm. Applicability is demonstrated by comparative measurement of 4-methyl-2-oxopentanoate content in plasma of patients with maple syrup urine disease by the enzymatic and a reversed phase high performance liquid chromatographic method.

Monitoring of phenylketonuria: a colorimetric method for the determination of plasma phenylalanine using L-phenylalanine dehydrogenase

A simple, rapid, accurate, and precise colorimetric assay for the determination of L-phenylalanine in plasma samples using L-phenylalanine dehydrogenase [L-phenylalanine:NAD+-oxidoreductase (deaminating)] from Rhodococcus sp. M 4 is described. The enzyme catalyzes the NAD-dependent oxidative deamination of L-phenylalanine. However, the equilibrium of reaction favors L-phenylalanine formation. By stoichiometric coupling of this reaction with diaphorase/iodonitro tetrazolium chloride (INT) the formed NADH converts INT to a formazan whereby the reaction is displaced in favor of phenylpyruvate. Using a kinetic approach the increase in absorbance at 492 nm shows linearity over more than 30 min. Deproteinized standard solutions of L-phenylalanine in the range from 30 to 1200 mumol/liter show a linearity between the dAformazan/30 min and the substrate concentration. In phenylketonuria (PKU) plasma samples no interferences caused by L-tyrosine or phenylpyruvic acid are seen. Applicability is demonstrated by comparative determination of plasma L-phenylalanine of treated PKU patients by the colorimetric method and automated amino acid analysis.

[A computer program for registering all daily accumulated data at a school for vision disorders]

Despite increasing medical use of the computer, many clinics have experienced only limited success (or none at all) in computerized registration of patient data. One important reason for this lies in the complicated user interfaces of most programs. The clinician has no time to familiarize himself with the complicated command sequences involved, while necessary acceptance of the new technology by administrative staff is often lacking. This paper shows that computerized registration and interpretation of patient data are well within the bounds of possibility, given the use of newly-developed user-friendly operating systems and suitable personal computers. A concrete example of computerized registration of data in a remedial center is given: a case with squint symptoms for which 176 parameters can be entered.

Enzymatic determination of L-phenylalanine and phenylpyruvate with L-phenylalanine dehydrogenase

An enzymatic method is described for the determination of L-phenylalanine or phenylpyruvate using L-phenylalanine dehydrogenase. The enzyme catalyzes the NAD-dependent oxidative deamination of L-phenylalanine or the reductive amination of the 2-oxoacid, respectively. The stoichiometric coupling of the coenzyme allows a direct spectrophotometric assay of the substrate concentration. The equilibrium of the reaction favors L-phenylalanine formation; however, by measuring initial reaction velocities, the enzyme can be used for L-phenylalanine determination, too. Standard solutions of L-phenylalanine in the range of 10-300 microM and of phenylpyruvate (5-100 microM) show a linearity between the value for dENADH/min and the substrate concentration. Besides phenylalanine, the enzyme can convert tyrosine and methionine, and their oxoacids, respectively. The Km values of these substrates are higher. The influence of tyrosine on the determination of phenylalanine was studied and appeared tolerable for certain applications.

[A new procedure for the direct demonstration of microbial aminoacylase on agar plates with o-phthalaldehyde]

Not less than 1 nmol of methionine and phenylalanine were detected as fluorescent spots on agar plates with o-phthalaldehyde reagent under UV light. Microorganisms were grown on thin-agar-layer coated filter papers placed on nutrient agar plates, and then transferred onto new plates lacking nutrients by moving the papers. After the background amino compounds were removed by the diffusion to the bottom plates, the paper cultures were moved and incubated on assay plates containing N-acetylmethionine or N-acetylphenylalanine. The amino acids formed around the colonies were visualized by the o-phthaladehyde procedure to indicate aminoacylase activity of microorganisms. The substrate-and stereospecificity of the enzyme was shown for some strains on the agar plates by this procedure.

Characterization of hydantoinase from Pseudomonas fluorescens strain DSM 84

The hydantoinase (EC 3.5.2.2) from Pseudomonas fluorescens strain DSM 84 was purified either by hydrophobic interaction chromatography on phenyl-Sepharose or by salting out chromatography on Sepharose 4B, gel filtration on Sephacryl S-400, and preparative electrophoresis. Molecular weight values of 230,000 and 60,000 for the native enzyme and each of the four subunits were estimated for the hydantoin hydrolysing activity. The hydantoinase was stable at temperatures up to 40 degrees C but showed an optimal activity at 55 degrees C. The enzyme was markedly inhibited by copper, para-hydroxymercuribenzoate, 8-hydroxyquinoline, and 2,2'-dipyridyl but not by zinc, and poorly by EDTA and o-phenanthroline. The hydantoin-hydrolyzing activity could be reactivated by ferrous ions. Dihydrouracil was the most readily hydrolyzed substrate. The dihydropyrimidinase produced by strain DSM 84 could also hydrolyze 5-substituted hydantions such as isopropylhydantoin (valine derivative) continuously for 10 days in a membrane reactor at a conversion rate of 30%. The only identified end product was N-carbamyl-D-valine.