Electric-field-enhanced selective separation of products of an enzymatic reaction in a membrane micro-contactor

Processes employed in separations of products of enzyme reactions are often driven by diffusion, and their efficiency can be limited. Here, we exploit the effect of a direct current (DC) electric field that intensifies mass transfer through a semipermeable membrane for fast, continuous, and selective separation of electrically charged molecules. Specifically, we separate low-molecular-weight reaction products (phenylacetic acid, 6-aminopenicillanic acid) from the original reaction mixture containing a free enzyme (penicillin acylase). The developed microfluidic dialysis-membrane contactor allows a stable counter-current arrangement of the retentate and permeates liquid streams on which DC electric field is perpendicularly applied. The applied electric field significantly accelerates the transport of electrically charged products through the semipermeable membrane yielding high separation efficiencies at short residence times. The residence time of 5 min is sufficient to reach 100% separation yield in the electric field. The same residence time provides only a 50% yield in the diffusion-controlled experiments. We experimentally demonstrated that a combined microreactor-microextractor with a recycle of the soluble penicillin acylase can continuously produce both the reaction products at high concentrations. The developed membrane-contactor is a versatile platform allowing to tune its characteristics, such as selectivity given by the membrane, or the type of the retentate phase, for a specific application.

[Serum levels of periostin and their influencing factors in the beta-lactam antibiotic enterprise workers]

Objective: To observe serum levels of periostin, ECP, IgE in the antibiotic enterprise workers, and study the role of periostin, ECP, IgE in the development of allergic inflammation. Methods: 90 cases with asthma or rhinitis were enrolled as disease group, another 117 workers exposed to 7-ACA、6-APA dust without suffering from allergic illness, are chosen as group of dust exposed, and 192 healthy workers who didn't contact dust were chosen as control group. Questionnaires were used to learn their basic information.Lung function was determined with a portable spirometer.The expression levels of periostin、ECP and IgE in serum were measured by enzyme-linked immuno sorbent assay. Results: The exposure group and disease group had significantly lower forced vital capacity (FVC) , forced expiratory volume in 1 second (FEV(l.0)) , and FEV(l.0)/FVC ratio than the control group (P<0.05) . The disease group had significantly higher eosinophil than the control group (P<0.05) . Compared with the control group, the exposure group, the disease group, asthma subgroup, rhinitis subgroup of serum periostin and IgE increased, the differences are statistically significant (P<0.05) . Serum levels of ECP in the workers of asthma subgroup were significantly higher than that in control group (P<0.05) . Serum expression levels of periostin were positively correlated with IgE, ECP in workers (P<0.001) , serum levels of periostin were negatively correlated with FEV(1.0) in workers (P<0.05) . Multiple logistics regression analysis found that exposure to 7-ACA or 6-APA (OR=3.09, 95%CI: 1.83-5.21) , age>47years (OR=2.53, 95%CI: 1.22-5.26) , higher ECP (OR=1.04, 95%CI: 1.01-1.06) were risk factors for increased serum periostin level. Conclusion: Occupational exposure to 7-ACA or 6-APA can result in higher serum periostin level, exposure to 7-ACA or 6-APA, age>47 years, higher ECP are risk factors for increased serum periostin level.

Optimization of aqueous two-phase systems for the production of 6-aminopenicillanic acid in integrated microfluidic reactors-separators

Aqueous two-phase systems (ATPSs) were screened for the production of 6-aminopenicillanic acid (6-APA) catalyzed by penicillin acylase, followed by the extractive separation of 6-APA from the reaction mixture. The key point of this study was to find an ATPS exhibiting a large difference in the partition coefficients of the biocatalyst and reaction products. Several ATPSs based on polyethylene glycol (PEG)/phosphate, PEG/citrate, and PEG/dextran were tested. We found that an ATPS consisting of 15 wt% of PEG 4000, 10 wt% of phosphates, 75 wt% of water (pH value 8.0 after dissolution) provided optimal separation of 6-APA from the enzyme. While the 6-APA was mainly found in the top PEG phase, the free enzyme favored the bottom salt-rich phase. This ATPS also fulfils other important requirements: (i) high buffering capacity, reducing an undesirable pH decrease due to the dissociation of phenylacetic acid (the side product of the reaction), (ii) a relatively low cost of the ATPS components, (iii) the possibility of electrophoretic transport of fine droplets as well as the reaction products for both the acceleration of phase separation and the enhancement of 6-APA concentration in the product stream. Extraction experiments in microcapillary and batch systems showed that the transport of 6-APA formed in the salt-rich phase to the corresponding PEG phase could occur within 30 s. The experimental results described form a base of knowledge for the development of continuously operating integrated microfluidic reactors-separators driven by an electric field for the efficient production of 6-APA.

Inactivation of D-alanine carboxypeptidase by penicillins and cephalosporins is not lethal in Bacillus subtilis

The D-alanine carboxypeptidase of Bacillus subtilis is a particulate enzyme that is irreversibly inactivated by penicillins and cephalosporins. However, the lethal concentrations of these antibiotics are not the same as those that inhibit enzymatic activity in vitro. 6-Aminopenicillanic acid inactivates at least 95% of the enzyme at nonlethal concentrations. Conversely, cephalothin is lethal at concentrations that do not inactivate the enzyme. Experiments with intact, growing cells confirm the results obtained in vitro. Therefore, a killing site distinct from the carboxypeptidase must be postulated.