Immobilization of penicillin G acylase on aminoalkylated polyacrylic supports

Investigation of Polyacrylic Acid Toxicity in Human Breast Cancer (MCF-7) and Mouse Fibroblast (L-929) Cell Lines

In recent years, biopolymers have been widely used in various fields of medicine. Before using any polymer, its biocompatibility should be examined. Polyacrylic acid (PAA), a polyelectrolyte, is known to be used as an adjuvant effect in immunology, anti-thrombogenic effect in medical experiments, and as a carrier in drug delivery systems. Although there are studies on various conjugates and nanoparticles of PAA, studies on its toxicity alone are limited. Determination of toxicity in biopolymer studies is extremely important. Cultures of various cells are used for toxicity analyses. This study aimed to investigate the toxicity of PAA in human breast cancer (MCF-7) and mouse fibroblast (L-929) cell lines by various methods. Cell culture, 3-(4,5-dimethyltriazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), trypan blue and 4,6-diamidino 2 phenylindole (DAPI) methods were used in the study. The half-maximal effective concentration (EC50) value of PAA was 6.6 mg/ml in MCF 7 cells and 1.8 mg/ ml in L-929 cells. Apoptosis was observed in cells on the increasing PAA concentration with DAPI. With these results, the cytotoxic properties of PAA were determined in vitro. Accordingly, the biocompatibility of polymers to be used in modeling should be supported by in vitro and in vivo studies.

A comparison of two colorimetric assays, based upon Lowry and Bradford techniques, to estimate total protein in soil extracts

Soil extracts usually contain large quantities of dissolved humified organic material, typically reflected by high polyphenolic content. Since polyphenols seriously confound quantification of extracted protein, minimising this interference is important to ensure measurements are representative. Although the Bradford colorimetric assay is used routinely in soil science for rapid quantification protein in soil-extracts, it has several limitations. We therefore investigated an alternative colorimetric technique based on the Lowry assay (frequently used to measure protein and humic substances as distinct pools in microbial biofilms). The accuracies of both the Bradford assay and a modified Lowry microplate method were compared in factorial combination. Protein was quantified in soil-extracts (extracted with citrate), including standard additions of model protein (BSA) and polyphenol (Sigma H1675-2). Using the Lowry microplate assay described, no interfering effects of citrate were detected even with concentrations up to 5 times greater than are typically used to extract soil protein. Moreover, the Bradford assay was found to be highly susceptible to two simultaneous and confounding artefacts: 1) the colour development due to added protein was greatly inhibited by polyphenol concentration, and 2) substantial colour development was caused directly by the polyphenol addition. In contrast, the Lowry method enabled distinction between colour development from protein and non-protein origin, providing a more accurate quantitative analysis. These results suggest that the modified-Lowry method is a more suitable measure of extract protein (defined by standard equivalents) because it is less confounded by the high polyphenolic content which is so typical of soil extracts.

Conjugation, characterization and toxicity of lipophosphoglycan-polyacrylic acid conjugate for vaccination against leishmaniasis

Research on the conjugates of synthetic polyelectrolytes with antigenic molecules, such as proteins, peptides, or carbohydrates, is an attractive area due to their highly immunogenic character in comparison to classical adjuvants. For example, polyacrylic acid (PAA) is a weak polyelectrolyte and has been used in several biomedical applications such as immunological studies, drug delivery, and enzyme immobilization. However, to our knowledge, there are no studies that document immune-stimulant properties of PAA in Leishmania infection. Therefore, we aimed to develop a potential vaccine candidate against leishmaniasis by covalently conjugating PAA with an immunologically vital molecule of lipophosphoglycan (LPG) found in Leishmania parasites. In the study, LPG and PAA were conjugated by a multi-step procedure, and final products were analyzed with GPC and MALDI-TOF MS techniques. In cytotoxicity experiments, LPG-PAA conjugates did not indicate toxic effects on L929 and J774 murine macrophage cells. We assume that LPG-PAA conjugate can be a potential vaccine candidate, and will be immunologically characterized in further studies to prove its potential.

Immobilization of penicillin G acylase on macro-mesoporous silica spheres

In this study, macro-mesoporous silica spheres were prepared with a micro-device and used as the support for the immobilization of penicillin G acylase (PGA). To measure the enzymatic activity, the silica spheres with immobilized PGA were placed into a packed-bed reactor, in which the hydrolysis of penicillin G was carried out. The influences of the residence time, the initial concentration of the substrate, the accumulation of the target product 6-aminopenicillanic acid, and the enzyme loading amount on the performance of the immobilized PGA were investigated. The introduction of macropores increased the enzyme loading amount and decreased the internal mass transfer resistance, and the results showed that the enzyme loading amount reached 895 mg/g (dry support), and the apparent enzymatic activity achieved up to 1033 U/g (dry support). In addition, the immobilized PGA was found to have great stability.

Synthesis and characterization of pseudo-affinity ligand for penicillin acylase purification

The aim of this work was to test a chromatographic affinity support containing methacryloyl antipyrine (MAAP) for penicillin acylase (PA) purification by using pure penicillin acylase and crude extract. First, MAAP as a pseudo-specific ligand was synthesized by using methacryloyl chloride and 4-aminoantipyrine. Polymer beads (average size diameter: 40-120 micro m) were prepared by suspension polymerization of ethylene glycol dimethacrylate (EGDMA) and MAAP. This approach for the preparation of adsorbent has several advantages over conventional preparation protocols. An expensive and time consuming step in the preparation of adsorbent is immobilization of a ligand to the adsorption matrix. In this procedure, affinity ligand MAAP acts as comonomer without further modification steps. Poly(EGDMA-MAAP) beads were characterized by FTIR, NMR and screen analysis. Elemental analysis of MAAP for nitrogen was estimated as 89.3 micro mol/g. The prepared adsorbent was then used for the capture of penicillin acylase in batch system. The maximum penicillin acylase adsorption capacity of the poly(EGDMA-MAAP) beads was found to be 82.2 mg/g at pH 5.0. Chromatography with crude feedstock resulted in 23.2-fold purification and 93% recovery with 1.0 M NaOH.

A new method for spectrophotometric assay of activity of cross-linked penicillin acylase aggregates

A new method for monitoring reactions catalyzed by an immobilized enzyme, cross-linked penicillin acylase aggregates (PA CLEA), is suggested. Appropriate chromogenic substrates for spectrophotometric assay of catalytic activity of immobilized enzyme were chosen and their kinetic parameters determined. Active sites in PA CLEA preparations were titrated by the suggested method; it is shown that almost all active sites are retained during immobilization. This method is characterized as highly expressive, simple, and precise and may be used for control of PA immobilization efficiency as well as for study of operational, thermal, and pH stability of immobilized enzyme preparations.

Novel reactive perstraction system applied to the hydrolysis of penicillin G

The activity of penicillin acylase has been studied in aqueous and organic solvents, as free enzyme as well as immobilized within the membrane of liquid-core capsules. The activity of the enzyme is inhibited by the accumulation of the products of the hydrolysis reaction, namely phenyl acetic acid (PAA). In order to overcome this inhibition a range of organic solvents were tested for use in in situ product recovery. Of these solvents dibutyl sebacate (DBS) was chosen due to the rapid extraction rate, the high logP and to facilitate capsule production. The extraction efficiency at pH 3.5 for PAA was >80% for phase ratios of >50% free solvent with partition coefficients of 8 and 0.7 for PAA and penicillin G (PenG), respectively, thereby showing that PAA could be selectively extracted at pH 3.5 and 25 degrees C. Liquid-core capsules containing DBS were shown to efficiently remove PAA selectively and the PAA could be effectively back-extracted and the capsules re-used in a three-stage process resulting in high product separation. Immobilization of penicillin acylase onto the capsule membranes resulted in increased operational stability of the enzyme and a very high enzyme activity. Over 53.3% of the PAA formed could be recovered in the capsule core with a concentration over sevenfold higher than in the aqueous phase. Higher extraction efficiencies could be obtained by varying the substrate concentration and number of capsules. The enzyme immobilized on capsules could be stored for over 4 months at pH 8 and 4 degrees C with no loss of activity. Over 80% of the initial activity could be recovered over five repeated batch cycles of the bioconversion process. The importance of capsular perstraction and reactive capsular perstraction has been clearly demonstrated.

Penicillin G acylase-based stationary phases: analytical applications

A review of Penicillin G Acylase (PGA)-based stationary phases is given, focusing on immobilisation methods, selection of immobilisation material and applications in chiral liquid chromatography. Two immobilization methods, namely "in situ" and "in batch" techniques, are described for the immobilisation of PGA on silica supports. Microparticulate and monolithic silica, both functionalized with aminopropyl- and epoxy-groups, were used in the development of the PGA immobilised enzyme reactor (IMER). The best results, in terms of PGA immobilised amount and enzyme activity, were obtained with the "in situ" immobilisation on epoxy monolithic silica. The use of PGA columns as enzyme reactors for the preparation of 6-APA and for the production of enantiomeric pure drugs in a one-step reaction in described. The review also covers the application of PGA-columns as chiral stationary phases for the separation of acidic enantiomers. An on-line chromatographic system based on the PGA-IMER combined with a switching valve to an analytical column is also described as a highly efficient tool to study the enantioselective hydrolyses properties of PGA. Finally a molecular modelling study is reported with the aim to give more insights into PGA-substrates interactions and to expand the application of these stationary phases as a chiral biocatalysts for pharmaceutical processes.

Production and characterization of liquid-core capsules made from cross-linked acrylamide copolymers for biotechnological applications

A novel chemistry has been developed for the production of capsules composed of a hydrophobic liquid core surrounded by a cross-linked polyacrylamide/alginate membrane. These liquid-core capsules may be used in capsular perstraction for the removal of inhibitory products from bioprocesses and bioconversions. They have the advantage of having a high surface area to promote rapid mass transfer, while separation of the organic core phase from the aqueous environment by the capsule membrane prevents the formation of stable emulsions and potential problems associated with toxicity of the organic phase for microbial cells or enzymes. Monodisperse spherical liquid-core capsules of between 800 microm and 1.6 mm diameter, with high mechanical resistance, have been prepared by co-extrusion, using the jet break-up technique. Capsules produced from a solution of MBA/total monomer (5%) were found to be more elastic and have a higher burst force when exposed to chelating agents such as phosphate or citrate. The mechanical resistance was unaffected by buffer solutions in the pH range 4-9 and after sterilization at 121 degrees C for 20 min. Capsules having membranes composed of a copolymer of acrylamide and N-hydroxymethylacrylamide exhibited even higher mechanical stability toward chelating agents.

Evaluation of a penicillin G acylase-based chiral stationary phase towards a series of 2-aryloxyalkanoic acids, isosteric analogs and 2-arylpropionic acids

The chiral recognition properties of a new chiral stationary phase based on immobilized penicillin G acylase were investigated using 35 acidic racemates. Twenty-seven compounds were resolved with high separation factors. The influences of mobile phase pH, type of organic modifier and ionic strength on enantioselective retention were studied. The most important tool for affecting the enantioselectivity was the mobile phase pH and interestingly the retention order of the enantiomers of some analytes could be controlled by this parameter. The analysis time for resolving enantiomers could be adjusted with a minor decrease in enantioselectivity using a high ionic strength mobile phase buffer while both retention and enantioselectivity decreased by adding organic modifier to the mobile phase. Displacement studies have demonstrated that the enzymatically active site and the chiral adsorption site overlap.

Immobilized penicillin G acylase as reactor and chiral selector in liquid chromatography

In this paper, the use of penicillin G acylase (PGA) as a biocatalyst and as a chiral selector is described. Penicillin G-acylase is an interesting enzyme used in the manufacture of semisynthetic antibiotics and, in particular, in the production of 6-APA by hydrolysis of penicillin G. Five PGA-based HPLC columns have been prepared by using two different silica supports by employing two immobilization methods, namely "in situ" and "in batch". The effects of the immobilization techniques and of different silica pore size on the catalytic properties of the enzyme as well as the applicability of the PGA-bonded stationary phases as chiral selectors for a number of chiral drugs have been investigated. The HPLC columns based on immobilized PGA combine the hydrolytic activity and the chiral recognition properties of PGA, therefore they have been used for the development of a combined reaction-separation system for chiral and achiral substrates.

Advances in enzymatic transformation of penicillins to 6-aminopenicillanic acid (6-APA)

This article elaborates on the important recent developments in the enzymatic transformation of penicillins to 6-aminopenicillanic acid (6-APA), which is the basic raw material for the industrial production of semisynthetic penicillins such as amoxycillin and ampicillin. Particular emphasis is placed on the improvements in purification, stability, and immobilization of the enzymes, (i.e. penicillin acylases) used for these transformations.