Specificity of Penicillin Acylases in Deprotection of N-Benzyloxycarbonyl Derivatives of Amino Acids.

Changes in the structure of the N-acyl group in N-acylated amino acid derivatives significantly affect both the recognition and activity of penicillin acylases on this series of substrates. However, penicillin acylases from both Alcaligenes faecalis and Escherichia coli are capable of removing the N-benzyloxycarbonyl protecting group in amino acid derivatives under mild conditions without the use of toxic reagents. Efficiency in using penicillin acylases in preparative organic synthesis can be improved by utilizing modern rational enzyme design methods.

Penicillin Acylase-Catalyzed Effective and Stereoselective Acylation of 1-phenylethylamine in Aqueous Medium using Non-Activated Acyl Donor.

Until recently, the biocatalytic preparation of enantiomerically pure amines was based on stereoselective acyl transfer in an organic medium using activated acyl donors. The possibility of performing an effective and enantioselective enzymatic acylation of amines in an aqueous medium without using activated acyl donors was demonstrated for the first time as the example of direct condensation of phenylacetic acid and racemic 1-phenylethylamine. Direct condensation of the acid and the amine took place at mild reaction conditions with a high initial rate (3.3 µmole/(l·h)), degree of conversion (80% acylation of active amine enantiomer), and enantioselectivity (enantiomeric excess of the product was more than 95%). The suggested approach has remarkable advantages compared to enzymatic reactions in organic media and is of practical value for the biocatalytic preparation of enantiomerically pure compounds at mild conditions using readily available reagents.

[The influence of acetyltransferase activity phenotype on the frequency of in-stent restenosis in patient with CHD].

Coronary artery stenting is a priority treatment of different forms of coronary heart disease. Hence, the importance of intrastent restenosis. This study demonstrates the relationship between acetylation rate and frequency of restenosis following coronary stenting with special reference to patients with chronic coronary heart disease. This knowledge may be helpful for the improvement of endovascular treatment using drug-coated stents.

Mutation of Residue ßF71 of Escherichia coli Penicillin Acylase Results in Enhanced Enantioselectivity and Improved Catalytic Properties.

Residue phenylalanine 71 of the ß-chain of penicillin acylase from E. coli is involved in substrate binding and chiral discrimination of its enantiomers. Different amino acid residues have been introduced at position ßF71, and the mutants were studied with respect to their enantioselectivity and substrate specificity. Some mutants demonstrated remarkably improved catalytic activity. Moreover, mutation of ßF71 residue allowed to enhance penicillin acylase enantioselectivity. The catalytic activity to the specific substrates was improved up to 36 times, most notably for K, R, and L mutants. Increased activity to a D-phenylglycine derivative - a valuable specificity improvement for biocatalytic synthesis of new penicillins and cephalosporins - was shown for ßF71R and ßF71L mutants. The synthetic capacity of penicillin acylase with 6-aminopenicillanic acid as an external nucleophile was especially sensitive to mutation of the ß71 residue in contrast to the synthesis with 7-aminodeacetoxycephalosporanic acid.

Chiral high-performance liquid chromatography analysis of alpha-amino acid mixtures using a novel SH reagent--N-R-mandelyl-L-cysteine and traditional enantiomeric thiols for precolumn derivatization.

Several chiral thiols, i.e. traditionally used enantiomerically pure SH reagents and novel N-R-mandelyl-L-cysteine (R-NMC) containing additional chiral center, have been applied as co-reagents in precolumn derivatization with o-phthalaldehyde for enantiomeric HPLC analysis of individual alpha-amino acids and their mixtures. The R-NMC-derived isoindoles as well as adducts with other thiols have a characteristic absorption maximum at 340 nm, and are highly fluorescent allowing detection of 10 microg/l of an amino acid. Investigated 19 amino acids were analyzed separately and in a mixture by a gradient HPLC after precolumn derivatization. The chromatographic behavior of formed isoindoles substantially differs for each of the thiols used for modification. In contrast to traditional enantiomeric thiols application of diastereomeric R-NMC provides higher resolution for alpha-amino acid enantiomers, with L,D-elution order (except for Arg). Combined use of R-NMC and other thiol enlarges the possibilities of this method, allowing accurate chiral analysis of complex amino acid mixtures.

Aliphatic amidase from Rhodococcus rhodochrous M8 is related to the nitrilase/cyanide hydratase family.

A comparative study of amino acid sequence and physicochemical properties indicates the affiliation of an amidase from Rhodococcus rhodochrous M8 (EC 3.5.1.4) to the nitrilase/cyanide hydratase family. Cluster analysis and multiple alignments show that Cys166 is an active site nucleophile. The enzyme has been shown to be a typical aliphatic amidase, being the most active toward short-chain linear amides. Small polar molecules such as hydroxylamine and O-methyl hydroxylamine can serve as effective external nucleophiles in acyl transfer reactions. The kinetics of the industrially important amidase-catalyzed acrylamide hydrolysis has been studied over a wide range of substrate concentrations; inhibition during enzymatic hydrolysis by the substrate and product (acrylic acid) has been observed; an adequate kinetic scheme has been evaluated and the corresponding kinetic parameters have been determined.

[A new N-acyl derivative of (S)-cysteine for quantitative determination of enantiomers of amino compounds by HPLC method with a precolumn modification with o-phthalaldehyde]. / Novoe N-atsil'noe proizvodnoe (S)-tsisteina dlia kolichestvennogo opredeleniia énantiomerov aminosoedineniii metodom VEZhKh s predkolonochnoi modifikatsiei opto-ftalevym al'degidom.

N-Phenylacetyl-(R)-phenylglycyl-(S)-cysteine (NPPC) was used for the determination of enantiomers of primary amines by rpHPLC with a precolumn modification with o-phthalaldehyde. NPPC was compared with the classic SH reagent N-acetyl-(S)-cysteine (NAC) in the analysis of stereomers of nonfunctionalized amines and amino alcohols. After the NAC modification, the resulting diastereomeric isoindoles were difficult to separate by HPLC, and satisfactory resolution was achieved only for some aliphatic amino alcohols. The use of NPPC improved the chromatographic analysis of stereomeric amino alcohols and, in addition, allowed the enantiomeric analysis of the nonfunctionalized amines. Similarity between the side radicals of the amino component and the thiol reagent favored the diastereomer separation. This method was used for determination of the absolute concentration of individual enantiomers of amines in the course of stereoselective enzymatic reactions. The optically active NPPC was prepared with a high yield by a chemoenzymatic synthesis based on a regioselective acylation of the (S)-cysteine amino group in aqueous medium by the action of penicillin acylase. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 5; see also http: // www.maik.ru.

pH Stability of penicillin acylase from Escherichia coli.

The inactivation kinetics of penicillin acylase from Escherichia coli have been investigated over a wide pH range at 25 and 50 degrees C. The enzyme was very stable in neutral solutions and quickly lost its catalytic activity in acidic and alkaline solutions. In all cases, the inactivation proceeded according to first order reaction kinetics. Analysis of the pH dependence of enzyme stability provides evidence that stable penicillin acylase conformation is maintained by salt bridges. Destruction of the salt bridges due to protonation/deprotonation of the amino acid residues forming these ion pairs causes inactivation by formation of the unstable "acidic" EH(4)(3+), EH(3)(2+), EH(2)(+) and "alkaline" E(-) enzyme forms. At temperatures above 35 degrees C penicillin acylase apparently undergoes a conformational change that is accompanied by destruction of one of these salt bridges and change in the catalytic properties.

The role of hydrophobic interactions on alcohol binding in the active center of penicillin acylases.

Inhibition of penicillin acylases from Escherichia coli and Alcaligenes faecalis by aliphatic and aromatic alcohols was studied. It was shown that the inhibition of both enzymes has competitive nature and they bind the alcohols at the acyl group binding site of the enzyme active center. The free energy of alcohol sorption was shown to be linearly dependent on the hydrophobicity of the inhibitor with slopes of 1.6 and 1.7, demonstrating extremely effective hydrophobic interactions. To rationalize the observed distinctions in the inhibiting properties of aromatic and aliphatic alcohols beginning with butanol, it was suggested that the loss of entropy occurring on the interaction of the ligand with the tightly restricted hydrophobic pocket of the active center makes an essential contribution to the overall energetics of complex formation.