Mixed Carbonates as Useful Substrates for a Fluorogenic Assay for Lipases and Esterases

The influence of UV light on the course of fluorescent enzyme assays

Experiments were carried out to illustrate the effect of UV light on the course of the enzymatic reaction of the coumarin derivative. Only the pulsating light of the UV diode gives the correct results for the determination of the kinetic constants of the enzymatic reaction. The enzyme concentration limit was found where the description of the M-M model breaks. It was shown that the system determines the kinetic parameters of enzymatic reactions: V_max-the maximum rate of reaction and K_M-the Michaelis constant. This method produces kinetic constants calculated from the changes in enzyme product concentration using the Michaelis-Menten model. To verify the results, we used a statistical analysis that checks the correctness of the model used.

Integrin-Mediated Targeted Cancer Therapy Using c(RGDyK)-Based Conjugates of Gemcitabine

c(RGDyK)-based conjugates of gemcitabine (GEM) with the carbonate and carbamate linkages in the 6-OH group of GEM were synthesized for the targeted delivery of GEM to integrin α_vβ₃, overexpressing cancer cells to increase the stability as well as the tumor delivery of GEM and minimize common side effects associated with GEM treatment. Competitive cell uptake experiments demonstrated that conjugate TC113 could be internalized by A549 cells through integrin α_vβ₃. Among the synthesized conjugates, TC113 bearing the carbamate linker was stable in human plasma and was further assessed in an in vivo pharmacokinetic study. TC113 appeared to be relatively stable, releasing GEM slowly into blood, while it showed potent antiproliferative properties against WM266.4 and A549 cells. The encouraging data presented in this study with respect to TC113 provide a promising keystone for further investigation of this GEM conjugate with potential future clinical applications.

Multifunctional Near-Infrared Fluorescent Probes with Different Ring-Structure Trigger Groups for Cell Health Monitoring and In Vivo Esterase Activity Detection

A series of multifunctional ratiometric near-infrared fluorescent probes (CYOH-3, CYOH-4, CYOH-5, and CYOH-6) for esterase detection are designed by gradually changing the deflection of the plane twist in the molecule. These probes are composed of different ring-structure trigger groups (from three-membered ring to six-membered ring) and the same luminescent group CYOH. These probes show maximum absorption at ∼585 nm and a fluorescence emission peak at ∼655 ± 5 nm. In the presence of esterase, the probes were hydrolyzed to expose the fluorophore CYOH (λ_abs = 690 nm, λ_em = 710 ± 5 nm), thus exhibiting ratiometric near-infrared fluorescence. The probe CYOH-6 has lower plane deflection angle and better ratiometric (R = I_710±5nm/I_657±4nm) fluorescence properties than probes CYOH-3, CYOH-4, and CYOH-5. CYOH-6 (six-membered ring) has been successfully used to target esterase in mitochondria and distinguish between dead cells (esterase inactivation) and live cells. In addition, CYOH-6 has been well used for monitoring of esterase activity in zebrafish and mice, which proves that these probes have good prospects for clinical biomedical applications.

Indoxyl Acetate as a Substrate for Analysis of Lipase Activity

Lipases play a crucial role in metabolism of microbes, fungi, plants, and animals, and in analytical chemistry, they are often used in detection of fats and triglycerides. Determination of lipase activity is also important in toxicology, when lipase activity can be both increased and decreased by organophosphates and other pesticides and in medicine for diagnosis of heart diseases. The standard method for lipase activity determination is based on cleaving ester bonds in lipase buffer containing Tween. Our aim was to find a method with faster and more sensitive response. It is known that acetylcholinesterase belongs to the same group of hydrolases enzymes as lipases and it cleaves indoxyl acetate, so we assume indoxyl acetate could report a similar reaction with lipase. Our method is based on indoxyl acetate as a substrate for lipase, where indoxyl acetate is cleaved by lipase to indoxyl and acetate moiety and blue indigo is created. The method was optimized for different times and amount of enzyme and compared with the standard Tween assay. The calibration curve measured in reaction time 20 minutes with 10 μl of lipase exhibited the best analytical parameters, and it showed Michaelis-Menten response with the Michaelis-Menten constant equal to 8.72 mmol/l. The indoxyl acetate-based method showed faster and more sensitive response than the standard method for lipase activity determination, so it has great potential in biosensor construction and it could be used in industry, medicine, toxicology, and common practice where the activity of lipases is need to be measured.

Evaluation of droplet-based microfluidic platforms as a convenient tool for lipases and esterases assays

The accurate estimation of kinetic parameters is of fundamental importance for biochemical studies for research and industry. In this paper, we demonstrate the application of a modular microfluidic system for execution of enzyme assays that allow determining the kinetic parameters of the enzymatic reactions such as V_max - the maximum rate of reaction and K_M - the Michaelis constant. For experiments, the fluorogenic carbonate as a probe for a rapid determination of the kinetic parameters of hydrolases, such as lipases and esterases, was used. The microfluidic system together with the method described yields the kinetic constants calculated from the concentration of enzymatic product changes via a Michaelis-Menten model using the Lambert function W(x). This modular microfluidic system was validated on three selected enzymes (hydrolases).

Self-immolative versatile fluorogenic probes for screening of hydrolytic enzyme activity

Enzyme triggered probes with a self-immolative linker for rapid and sensitive hydrolase detection through a cascade reaction have been reported. Their utility was proved by the preparation of three model compounds and their evaluation as enzyme substrates and demonstration of their applicability as fluorogenic probes for screening lipase, esterase and protease activities. These probes represent a new class of fluorogenic compounds, are stable under aqueous conditions and not susceptible to nonspecific degradation. The utilization of the carbamate cleavable linkage in a probe structure allows moving away of the bulky fluorophore from the enzyme recognition unit and targets different classes of enzymes with the same substrate.

Novel 4-Methylumbelliferone Amide Derivatives: Synthesis, Characterization and Pesticidal Activities

A series of novel 4-methylumbelliferone amide derivatives were designed, synthesized and characterized by ¹H NMR, ¹³C NMR and HR-ESI-MS. The structures of compounds 4bd and 4be (compounds named by authors) were further confirmed by X-ray single crystal diffraction. The acaricidal, herbicidal and antifungal activities of the synthesized compounds were assayed for their potential use as pesticide. The results indicated that compounds 4bi, 4ac and 4bd were strong acaricidals against Tetranychus cinnabarinus, with 72h corrected mortalities of greater than 80% at 1000 mg/L. Meanwhile, compounds 4bh and 4bf exhibit the strongest inhibition against the taproot development of Digitaria sanguinalis and Chenopodium glaucum, and were even more potent than the commercial herbicide Acetochlor against D. sanguinalis. In addition, compounds 4bk, 4bh and 4bp showed the highest antifungal activity against the mycelium growth of Valsa mali, which makes them more effective than commercial fungicide Carbendazim.

Biosensing strategies based on enzymatic reactions and nanoparticles

Application of new nanomaterials to detection of enzymatic activities allows the development of new sensitive and selective bioanalytical assays based on enzymes for recognition and signal amplification.

High-Throughput Screening Assays for Lipolytic Enzymes

Screening is defined as the identification of hits within a large library of variants of an enzyme or protein with a predefined property. In theory, each variant present in the respective library needs to be assayed; however, to save time and consumables, many screening regimes involve a primary round to identify clones producing active enzymes. Such primary or prescreenings for lipolytic enzyme activity are often carried out on agar plates containing pH indicators or substrates as triolein or tributyrin. Subsequently, high-throughput screening assays are usually performed in microtiter plate (MTP) format using chromogenic or fluorogenic substrates and, if available, automated liquid handling robotics. Here, we describe different assay systems to determine the activity and enantioselectivity of lipases and esterases as well as the synthesis of several substrates. We also report on the construction of a complete site saturation library derived from lipase A of Bacillus subtilis and its testing for detergent tolerance. This approach allows for the identification of amino acids affecting sensitivity or resistance against different detergents.

Efficient Passerini reactions in an aqueous vesicle system

The formation of α-acyloxy carboxamides from a carboxylic acid, an aldehyde and an isocyanide (Passerini reaction) was investigated in aqueous solution in the presence of different types of surfactants.