Stereochemistry of the reaction catalysed by 2-aminoethylphosphonate aminotransferase. A 1H-NMR study

(R)- and (S)-2-amino[2-D1]ethylphosphonic acids ([2-D1]AEP) were synthesised to investigate the stereochemistry of the reaction catalysed by 2-aminoethlphosphonate aminotransferase from Pseudomonas aeruginosa. This enzyme catalyses the transfer of the amino group of AEP to pyruvate to produce 2-phosphonoacetaldehyde and alanine. The enzymic reaction proceeding through the abstraction of a proton from the Schiff-base complex formed between the enzyme-bound pyridoxal 5'-phosphate, and the substrate, was carried out in an aqueous buffer at pH 8.5; it was followed by high-field 1H-NMR measurements (500 MHz, H2O) on an AMX 500 Bruker spectrometer. The spectra, recorded with chiral (R)- or (S)-[2-D1]AEP, both showed the methylenic signal (3.0 ppm), whereas (S)-[2-D1]AEP gave the additional aldehydic signal (CHO, 9.6 ppm). These data clearly show that AEP-aminotransferase catalyses the abstraction of the pro-S hydrogen atom at the prochiral C2 carbon of AEP. Furthermore, careful timing of NMR measurements over a 2-hour period allows us to show the occurrence of an isotopic effect.

Utilization of 2-aminoethylarsonic acid in Pseudomonas aeruginosa

This paper describes the metabolism, transport and growth inhibition effects of 2-aminoethylarsonic acid (AEA) and 3-aminopropylarsonic acid (APrA). The former compound supported growth of Pseudomonas aeruginosa, as sole nitrogen source. The two arsonates inhibited the growth of this bacterium when 2-aminoethylphosphonic acid (AEP) but not alanine or NH4Cl, was supplied as the only other nitrogen source. The analogy between AEA and the natural compound AEP led us to examine the in vitro and in vivo interaction of AEA with the enzymes of AEP metabolism. The uptake system for AEP (Km 6 microM) was found to be competitively inhibited by AEA and APrA (Ki 18 microM for each). AEP-aminotransferase was found to act on AEA with a Km of 4 mM (3.85 mM for AEP). Alanine and 2-arsonoacetaldehyde was generated concomitantly, in a stoichiometric reaction. In vivo, AEA was catabolized by the AEP-aminotransferase since it was able to first induce this enzyme, then to be an efficient substrate. The lower growth observed may have been due to the slowness with which the permease and the aminotransferase were induced, and hence to a poor supply of alanine by transamination.

Allosteric regulation of phosphonoacetaldehyde hydrolase by n-butylphosphonic acid

The effect of n-butylphosphonic acid on the activity of phosphonoacetaldehyde hydrolase from Pseudomonas aeruginosa was investigated: at low concentrations this compound appeared as an activator of the enzyme activity, whereas at higher concentrations it exhibited inhibitory properties. The experimental results were modelled according to an allosteric model involving two different classes of sites for n-butylphosphonic acid.

Phosphonoacetaldehyde hydrolase from Pseudomonas aeruginosa: purification properties and comparison with Bacillus cereus enzyme

Phosphonoacetaldehyde hydrolase (2-oxoethylphosphonate phosphonohydrolase, EC 3.11.1.1) has been purified to electrophoretic homogeneity from cells of Pseudomonas aeruginosa A 237 grown in a culture medium containing 2-aminoethylphosphonate as both phosphorus and carbon sources. The native Mr has been estimated to be 62,000 +/- 2000, using a gel filtration column equilibrated with standard proteins. A subunit of Mr 30,000 +/- 1000 determined in sodium dodecyl sulfate-polyacrylamide gel electrophoresis gives evidence of a homodimeric structure. The enzyme, which catalyzes the C-P bond cleavage of phosphonoacetaldehyde, has a Km value of 210 microM. It is moderately inhibited by methyl-, ethyl-, propyl- and butylphosphonic acids and activated by aminomethyl-, aminoethylphosphonic acids as well as by phosphonoformic, phosphonoacetic and phosphonopropionic acids. Inhibition by orthophosphite is a time-dependent process which exhibits first-order kinetics and is enhanced by the presence of acetaldehyde. Assays for phosphite removal by dilution or dialysis do not reverse the inhibition. Phosphonoacetaldehyde hydrolase inactivation by phosphite ion appears to be inconsistent with the concept of a Schiff base intermediate as proposed for Bacillus cereus enzyme.

(1-Amino-2-propenyl) phosphonic acid, an inhibitor of alanine racemase and D-alanine:D-alanine ligase

DL-(1-Amino-2-propenyl)phosphonic acid was synthesized through the sequential oxidation, sulfoxide elimination, and deprotection of diphenyl [1-[(benzyloxycarbonyl)amino]-3-(phenylthio)propyl] phosphonate. This analogue of vinylglycine is a strong inhibitor of the alanine racemases from Pseudomonas aeruginosa and Streptococcus faecalis and of the D-Ala:D-Ala ligase from this latter species. This molecule is ineffective against the whole bacterial cells. Unlike vinylglycine, this unsaturated phosphonate does not inhibit the following mammalian enzymes: aspartate aminotransferase, alanine aminotransferase, D-amino acid oxidase, which indicates its specificity. Thus, its incorporation in a peptide structure could induce interesting antimicrobial properties.

(beta-Chloro-alpha-aminoethyl)phosphonic acids as inhibitors of alanine racemase and D-alanine:D-alanine ligase

The (beta-chloro-, (beta, beta-dichloro-, and (beta, beta, beta-trichloro-alpha-aminoethyl)phosphonic acids have been synthesized and their inhibitory properties on the alanine racemases [EC 5.1.1.1] and the D-Ala:D-Ala ligases [EC 6.3.2.4] from Pseudomonas aeruginosa and Streptococcus faecalis have been evaluated. The monochloro and the dichloro derivatives of Ala-P exhibit a strong inhibition on the racemases of the two species tested but do not behave as suicide substrates. Only the D-Ala:D-Ala ligase of S. faecalis is inhibited by these compounds. The poor antibacterial activity observed with beta-chloro- and beta, beta-dichloro-Ala-P might be enhanced by the peptide-transport strategy.

Effect of phosphonic analogues of glutamic acid on glutamate decarboxylase

Among the phosphonic analogues of glutamic acid, only 4-amino-4-phosphono butyric acid, the compound which shows the highest affinity for pyridoxal phosphate, inhibits competitively both Escherichia coli and rat brain glutamate decarboxylases. Phosphinothricin, 2-amino-4-(methylphosphino)butyric acid, is a strong inhibitor of the mammalian enzyme.

Purification and properties of 2-aminoethylphosphonate:pyruvate aminotransferase from Pseudomonas aeruginosa

2-Aminoethylphosphonate aminotransferase has been purified to homogeneity with a yield of 15% from cell extracts of Pseudomonas aeruginosa. The molecular weight of the enzyme was estimated by gel filtration to be 65000 +/- 2000. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis yielded a molecular weight of 16500 +/- 1000, suggesting a tetrameric model for this protein. The absorption spectrum exhibits maxima at 280 nm, 335 nm and 415 nm which are characteristic of a pyridoxal-phosphate-dependent enzyme: 4 mol of pyridoxal 5'-phosphate/mol of enzyme have been found. This aminotransferase catalyzes the transfer of the amino group of 2-aminoethylphosphonate (ciliatine) to pyruvate to give 2-phosphonoacetaldehyde and alanine. A pH optimum between 8.5-9 and an activity increasing from 30 degrees C to 50 degrees C have been observed. The reaction follows Michaelis-Menten kinetics with Km values of 3.85 mM and 3.5 mM for ciliatine and pyruvate respectively. This enzyme shows a very high specificity since ciliatine and pyruvate are the only amino donor and acceptor respectively. Methyl, ethyl and propylphosphonic acids are better competitors towards ciliatine than their alpha-amino derivatives. 3-Aminopropylphosphonate, the higher homologue of ciliatine, is recognized neither as a substrate nor as an inhibitor. The enzyme activity is significantly affected by carbonyl reagents and by HgCl2. Transamination of 2-aminoethylphosphonate is the first step of a double-step pathway which leads to the cleavage of its C-P bond.

[Utilization of various omega-guanidoalkylphosphonic acids by Pseudomonas aeruginosa]

Bacterial growth was studied in synthetic media containing guanidomethyl-, 2-guanidoethyl-, 3-guanidopropyl- or 4-guanido-1-aminobutyl-phosphonic acid, as a possible nitrogen or phosphorus source. Among these four compounds, 2-guanidoethylphosphonic acid (2-GEPh) appeared to be the only efficient nitrogen nutrient. Our results are discussed in light of recent data on Pseudomonas aeruginosa amidinohydrolases. In addition, 2-GEPh proved to be a valuable source of phosphorus; the phosphorus group of its higher homologue 3-guanidopropylphosphonic acid was also used, but the linear bacterial growth curve reflected a limited rate of phosphate release. The characterization of ethylguanidine and propylguanidine in the corresponding culture filtrates suggests a hydrolytic process similar to that described for 3-aminopropylphosphonic acid.

[2-Amino-ethylphosphonic acid transport in Pseudomonas aeruginosa]

2-Aminoethylphosphonic acid (ciliatine) can be used as a source of phosphorus or nitrogen by Pseudomonas aeruginosa. The conditions of its uptake have been investigated. The transport is inducible by ciliatine itself or by its homologue, 3-aminopropylphosphonate, but neither by other phosphonic compounds nor by carboxylic or sulfonic related derivatives. The induction was not suppressed by inorganic phosphate. The transport appears to be an active process, pH and temperature dependent: it requires energy and is dependent on new protein synthesis. The uptake follows Michaelis kinetics. The substrate specificity involved in ciliatine uptake favours the existence of two different transport systems: the first one, inducible by ciliatine, was very sensitive towards different aminophosphonic acids and was competitively inhibited by inorganic phosphate and methylphosphonate; the second transport system, inducible by 3-amino-propylphosphonate, appeared less sensitive towards alpha-aminophosphonic acids and was non competitively inhibited by phosphate and methylphosphonate. No interactions were observed with related aminocarboxylic acids or with taurine. Some molecular structural requirements for the binding of an effector on both permeases are discussed. The regulatory function of inorganic phosphate, the chief breakdown product of ciliatine, is also emphasized.

[Research on the catabolism of phosphonic acids: biodegradation of the C-P bond by Pseudomonas aeruginosa]

3-Aminopropylphosphonic acid and 2-(beta-alanyl-amino)-ethylphosphonic acid can be used by Pseudomonas aeruginosa as a phosphorus source. Both compounds undergo a biodegradation through the cleavage of the C--P bond, without any modification upon the amino or amino-groups of the substrates.

In vivo incorporation of cytidine-monophosphate-ciliatine into rat liver lipids

1. In vivo this investigation was carried out in order to compare the incorporation into rat lipids of free [1,2-minus 14C]-ciliatine and CMP-[1,2-minus 14C]-ciliatine which is the precursor in phosphonolipid biosynthesis. 2. The incorporation of the radioactivity from CMP-[1,2-minus 14C]-ciliatine took place more rapidly than that from free [1,2-minus 14C]-ciliatine in both liver and kidney. The amount of radioactivity from the CMP-[1,2-minus 14C]-ciliatine incorporated into total liver lipids was about 5 times higher than that incorporated into total liver lipids of rat two hrs after injecting free-[1,2-minus 14C]-ciliatine. 3. The amount of [1,2-minus 14C]-ciliatine incorporated into total liver lipids was 15 and 21 times higher than that incorporated into total kidney lipids of rat two and four hrs after injecting free [1,2-minus 14C]-ciliatine. 4. If the main pathway for the phosphonolipid biosynthesis is via CMP-ciliatine, the rate of phosphonolipid formation from CMP-ciliatine must therefore be higher than that from free-ciliatine. The results obtained here indicate therefore that the main pathway for phosphonolipid biosynthesis is a pathway involving CMP-ciliatine. 5. An unknow compound was detected in the water soluble fraction of the acid hydrolyzate of liver phosphonolipids. This material migrated with the N-trimethyl-derivative of ciliatine on the thin-layer chromatogram. The result shows that there is therefore a possibility of methylation of exogenous ciliatine to the phosphonate analogue of choline in the mammalian body.