Acquisition of substrate-specific parameters during the catalytic reaction of penicillinase

The progress of the catalytic reaction of penicillinase (EC 3.5.2.6; penicillin amido-beta-lactamhydrolase) depends on the structure of the side-chain in derivatives of 6-aminopenicillanic acid (the parent substrate). Side-chains of one class promote the rate of the reaction and cause no deviation from the linear kinetics observed with the parent compound. By contrast, side-chains of the other class induce a time-dependent, reversible change in the parameters of the catalytic reaction. The rate decelerates considerably and then becomes constant; the decrease in kcat is accompanied by a corresponding decrease in Km. The initial parameters of the biphasic reaction, determined by stopped-flow spectrophotometry, approach those of the unsubstituted 6-aminopenicillanic acid. The final parameters, which are specific for each derivative, are not acquired when the native conformation of the enzyme is stabilized by homologous antibodies.

Enzyme-functionalized gold-coated magnetite nanoparticles as novel hybrid nanomaterials: synthesis, purification and control of enzyme function by low-frequency magnetic field

The possibility of remotely inducing a defined effect on NPs by means of electromagnetic radiation appears attractive. From a practical point of view, this effect opens horizons for remote control of drug release systems, as well as modulation of biochemical functions in cells. Gold-coated magnetite nanoparticles are perfect candidates for such application. Herein, we have successfully synthesized core-shell NPs having magnetite cores and gold shells modified with various sulphur containing ligands and developed a new, simple and robust procedure for the purification of the resulting nanoparticles. The carboxylic groups displayed at the surface of the NPs were utilized for NP conjugation with a model enzyme (ChT). In the present study, we report the effect of the low-frequency AC magnetic field on the catalytic activity of the immobilized ChT. We show that the enzyme activity decreases upon exposure of the NPs to the field.

In situ detection of beta-lactamase activity in sodium dodecyl sulfate-polyacrylamide gels

After beta-lactamase had been denatured by boiling in the presence of sodium dodecyl sulfate (SDS) and then electrophoresed in SDS-polyacrylamide gels, activity could be restored and could be detected in situ as specific molecular species. Renaturation was simple and facilitated by the presence of a carrier protein. The assay was sensitive, detecting 0.8 ng beta-lactamase activity in the gel.

Interaction of the pBR 322-coded RTEM beta-lactamase with substrates. Evidence for specific conformational transitions

The rate of inactivation of RTEM-1 beta-lactamase by Pronase is accelerated by class A ('resistant') penicillins. Other substrates (class S penicillin and cephalosporins) protect against the inactivation. Cefoxitin, a semi-synthetic cephamycin, induces a more extensive, hysteretic response. In its presence the enzyme is inactivated by trypsin as well as by Pronase.

Conformational adaptation of RTEM beta-lactamase to cefoxitin

Cefoxitin, a poor substrate of the RTEM beta-lactamase (penicillin amido-beta-lactam hydrolase, EC 3.5.2.6), induces a reversible change in the conformation of the enzyme. The change is manifested in gradual loss of catalytic activity and increased susceptibility to proteolytic inactivation. It is prevented by antibodies, which stabilize the native conformation. By contrast, divalent cations, which have no effect on the native enzyme, delay recovery from the cefoxitin-induced state, presumably by reacting with sites made accessible in the partly unfolded enzyme. Prolonged exposure to excess of cefoxitin causes a similar delay. The kinetic evidence, namely, the initial burst of consumption of cefoxitin and the subsequent gradual recovery of activity with better substrates, appears to be consistent with acylation of the active site by cefoxitin followed by a slower deacylation step [Fisher et al. (1980) Biochemistry 19, 2895-2901]. However, additional evidence leads us to conclude that the kinetics observed reflect deformation of the active site, rather than its blockage, by cefoxitin. Of most significance is the transient change in specificity, i. e. a preferential interaction of the recovering enzyme with substrates which are closest in structure to cefoxitin.

Simple photometric assay of beta-lactamase activity

A simple photometric assay of beta-lactamase activity was developed. The method is based on a decrease in optical density at 620 nm caused by the formation of a penicilloic acid-iodine complex. The enzymatic reaction is instantaneously stopped by the addition of a concentrated iodine-tungstate solution. Data showing the time and concentration dependence of the reaction are presented. By varying both the time of the assay and the concentration of the enzyme, substrates of widely different V(max) values could be assayed. The assay is compared with other methods of determining beta-lactamase activity.

Synthesis of 1,3-diaryl-spiro[azetidine-2,3′-indoline]-2′,4-dionesviathe Staudinger reaction:cis- ortrans-diastereoselectivity with different addition modes

A new synthetic approach for realizing biologically relevant bis-aryl spiro[azetidine-2,3′-indoline]-2′,4-diones was developed based on Staudinger ketene–imine cycloaddition through the one-pot reaction of substituted acetic acids and Schiff bases in the presence of oxalyl chloride and an organic base. A series of [azetidine-2,3′-indoline]-2′,4-diones were synthesized using this method. For comparison, the same compounds were obtained using a known technique, where ketene is generated from pre-synthesized acyl chloride. It was shown that the use of oxalyl chloride for ketene generation in the one-pot reaction at room temperature allows for the reversal of the diastereoselectivity of spiro-lactam formation, unlike previously described procedures.

Two experimental techniques of the ketene–imine Staudinger reaction allowed different diastereomers of spiro-indolinone-β-lactams to be obtained.

Synthesis and Biological Evaluation of S-, O- and Se-Containing Dispirooxindoles

A series of novel S-, O- and Se-containing dispirooxindole derivatives has been synthesized using 1,3-dipolar cycloaddition reaction of azomethine ylide generated from isatines and sarcosine at the double C=C bond of 5-indolidene-2-chalcogen-imidazolones (chalcogen was oxygen, sulfur or selenium). The cytotoxicity of these dispiro derivatives was evaluated in vitro using different tumor cell lines. Several molecules have demonstrated a considerable cytotoxicity against the panel and showed good selectivity towards colorectal carcinoma HCT116 p53^+/+ over HCT116 p53^−/− cells. In particular, good results have been obtained for LNCaP prostate cell line. The performed in silico study has revealed MDM2/p53 interaction as one of the possible targets for the synthesized molecules. However, in contrast to selectivity revealed during the cell-based evaluation and the results obtained in computational study, no significant p53 activation using a reporter construction in p53wt A549 cell line was observed in a relevant concentration range.

Alternative mechanism of action of the DNP PtIV prodrug: intracellular cisplatin release and the mitochondria-mediated apoptotic pathway

In a recent research paper Dr. Suxing Jin et al. reported two multispecific PtIV complexes DNP and NP with non-steroidal anti-inflammatory drug naproxen (NPX) as the axial ligand(s). Herein, we clarify the mechanism of action of DNP, its therapeutic target and intracellular redox-status.

Biotinylated Pt(IV) prodrugs with elevated lipophilicity and cytotoxicity

A design of Pt(IV) prodrugs with tumor cell targeting moieties leading to increased selectivity is of interest. Herein, we designed a novel Pt(IV) prodrugs with COX-inhibitor naproxen, long-chain hydrophobic stearic acid moiety and biotin as axial ligands. We have established that for Pt(IV) prodrugs with biotin and naproxen or stearate in axial position, the lipophilicity rather than biotin receptors expression is the main factor of cytotoxicity. We also monitored the reduction speed of Pt(IV) prodrug 3 with naproxen and biotin in axial positions in A549 cells using XANES and demonstrated that the prodrug gradually releases cisplatin within 20 hours of incubation.