Inhibition studies of soybean (Glycine max) urease with heavy metals, sodium salts of mineral acids, boric acid, and boronic acids

Synthesis and anti-ureolitic activity of Biginelli adducts derived from formylphenyl boronic acids

Urease is a metalloenzyme that contains two Ni(II) ions in its active site and catalyzes the hydrolysis of urea into ammonia and carbon dioxide. The development of effective urease inhibitors is crucial not only for mitigating nitrogen losses in agriculture but also for offering an alternative treatment against infections caused by resistant pathogens that utilize urease as a virulence factor. This study focuses on synthesizing and investigating the urease inhibition potential of Biginelli Adducts bearing a boric acid group. An unsubstituted or hydroxy-substituted boronic group in the Biginelli adducts structure enhances the urease inhibitory activity. Biophysical and kinetics studies revealed that the best Biginelli adduct (4e; IC50 = 132 ± 12 µmol/L) is a mixed inhibitor with higher affinity to the urease active site over an allosteric one. Docking studies confirm the interactions of 4e with residues essential for urease activity and demonstrate its potential to coordinate with the nickel atoms through the oxygen atoms of carbonyl or boronic acid groups. Overall, the Biginelli adduct 4e shows great potential as an additive for developing enhanced efficiency fertilizers and/or for medical applications.

Fabrication of multinuclear copper cluster-based coordination polymers as urease inhibitors

This study focused on the design and synthesis of two Cu-based coordination polymers, [Cu2(4-dpye)(5-HSIP)(μ3-O)(H2O)2]·3H2O (Cu-CP-1) and [Cu(4-dpye)0.5(BCA)2] (Cu-CP-2), where 4-dpye = N,N'-bis(4-pyridinecarboxamide)-1,2-ethane, 5-H3SIP = 5-sulfoisophthalic acid, and HBCA = benzoic acid, by using a hydrothermal method. Single-crystal X-ray diffraction (SCXRD) study revealed that by adding various auxiliary ligands, the architectures of the Cu-CPs could be altered, yielding two distinct multinuclear Cu clusters. Moreover, the Cu-CPs can be used as urease inhibitors (UIs). In vitro experiments showed that the Cu-CPs had good urease inhibition effects with IC50 values of 0.53 ± 0.01 μM for Cu-CP-1 and 1.44 ± 0.01 μM for Cu-CP-2 and 98.48% (Cu-CP-1) and 96.27% (Cu-CP-2) inhibition of urease was achieved at a concentration of 100 μM, respectively. Furthermore, the inhibition effect of the tetranuclear Cu-CP was better than that of the binuclear Cu-CP. To better understand the potential mechanism of inhibition of the two copper complexes, we performed kinetic analysis using Lineweaver-Burk (L-B) plots in the presence of different concentrations of urea and different concentrations of inhibitors, and both Cu-CP-1 and Cu-CP-2 showed a non-competitive mode of inhibition. In addition, molecular docking analysis showed that the Cu-CPs were able to enter well into the urease binding pocket, thus interacting with key amino acid residues of urease to different degrees. Both kinetic and molecular docking studies theoretically explain and demonstrate the inhibition effect of both Cu-CPs on urease activity in vitro, which is expected to provide reasonable guidance and effective strategies for the development of novel, efficient, stable and safe CP-based UIs.

Agro-physiological and soil microbial responses to desalinated seawater irrigation in two crops

Irrigation with desalinated seawater (DSW) is a potential solution for addressing water scarcity in semiarid regions across the globe. However, this strategy may compromise the health of agricultural ecosystems due to the high content of phytotoxic elements (mainly boron, B) in this water. Here, a three-year experiment was carried to evaluate the response of the soil's physicochemical and microbiological properties, and plant physiology, to three irrigation water treatments (DSW; fresh water, FW; and their blend (1:1), BW) in the presence or not of organic amendments. Lemon trees (Citrus limon (L.) Burm. fil. cv. Eureka), with a higher sensitivity to B toxicity, and apricot trees (Prunus armeniaca L. cv. 'Búlida'), with a lower one, were used as model plants. Lemon trees irrigated with BW and DSW showed a decline in net photosynthesis and stomatal conductance, and an accumulation of B in leaves that exceeded the toxicity threshold. These effects were stronger in amended soils. In soils cultivated with lemon trees, DSW irrigation increased the water-soluble nitrogen content, the urease activity, and the activity and biomass of the microbial community, and shifted the microbial community structure as compared with the other water treatments. The soil microbial community responses were controlled by the addition of organic amendments. The irrigation of apricots with DSW did not negatively impact plant physiological parameters but increased the soil microbial biomass, as in the case of the lemon tree-soil system. These results suggest that DSW irrigation increases soil microbial biomass in both crop-soil systems but harms the physiological status of the most sensitive crop. Our findings provide an initial approach to evaluate the response of the plant-soil system to DSW.

On-site urine treatment combining Ca(OH)2 dissolution and dehydration with ambient air

We present the results of three field tests and three laboratory tests of a new physical-chemical urine treatment system, which can recover all nutrients, while pathogens are inactivated. The system consists of two steps. In the first reactor, biological processes including urea hydrolysis are prevented by mixing fresh urine with calcium hydroxide (Ca(OH)₂). Due to the high pH value and the high availability of calcium, phosphate can be recovered by precipitation. The high pH value also fosters the inactivation of microorganisms, including pathogens. In the second reactor, water is evaporated at low energy consumption by blowing unheated ambient air over the stabilized urine. Stabilization in the first reactor was successful in all field and laboratory tests. The pH value remained between 12 and 13, except for short dips due to shortages of Ca(OH)₂. Nearly all phosphorus (92-96%) precipitated and could be recovered as calcium phosphate in the first reactor, while nitrogen and potassium overflowed with the urine into the evaporation reactor. The efficiency of the second treatment step was very different for field and laboratory experiments and depended on the duration of the experiment. During a four-day laboratory test, nitrogen recovery was 98%. In contrast, nitrogen recovery was only around 20% in the long-term field experiments. The high nitrogen losses occurred, because biological urea hydrolysis was not inhibited anymore, when the pH value in the second reactor decreased due to the dissolution of high amounts of carbon dioxide from the ambient air. Potassium was not subject to any significant loss, and the measured recovery in the solid evaporation product was 98%. Evaporation rates ranged between 50 g m^-2 h^-1 (RH = 82±13%, T = 12±6°C) and 130 g m^-2 h^-1 (RH = 60±19%, T = 24±5°C) in the three field tests. Apart from some disturbances due to low supply of Ca(OH)₂, the urine module functioned without any substantial failures and was simple to maintain. The minimum consumption of Ca(OH)₂ at full capacity was 6 g·L^-1 urine and the electricity demand was 150 Wh kg^-1 water evaporated from urine, resulting in operational costs of 0.05 EUR pers^-1 d^-1.

Inactivation of Jack Bean Urease by Nitidine Chloride from Zanthoxylum nitidum: Elucidation of Inhibitory Efficacy, Kinetics and Mechanism

Urease is a metalloenzyme that catalyzes the hydrolysis of urea into ammonia and carbon dioxide, which has a negative impact on human health and agriculture. In this study, the inactivation of jack bean urease by nitidine chloride (NC) was investigated to elucidate the inhibitory effect, kinetics, and underlying mechanism of action. The results showed that NC acted as a concentration- and time-dependent inhibitor with an IC₅₀ value of 33.2 ± 4.8 μM and exhibited a similar inhibitory effect to acetohydroxamic acid (IC₅₀ = 31.7 ± 5.8 μM). Further kinetic analysis demonstrated that NC was a slow-binding and non-competitive inhibitor for urease. Thiol-blocking reagents (dithiothreitol, glutathione, and l-cysteine) significantly retarded urease inactivation, while Ni²⁺ competitive inhibitors (boric acid and sodium fluoride) synergetically suppressed urease with NC, suggesting that the active site sulfhydryl groups were possibly obligatory for NC blocking urease. Molecular docking simulation further argued its inhibition mechanism. Additionally, NC-induced deactivation of urease was verified to be reversible since the inactivated enzyme could be reactivated by glutathione. Taking together, NC was a non-competitive inhibitor targeting the thiol group at the active site of urease with characteristics of concentration dependence, reversibility, and slow binding, serving as a promising novel urease suppressant.

Inhibition of urease activity by different compounds provides insight into the modulation and association of bacterial nickel import and ureolysis

The nickel-dependent urease enzyme is responsible for the hydrolysis of urea to ammonia and carbon dioxide. A number of bacteria produce urease (ureolytic bacteria) and are associated with various infectious diseases and ammonia emissions from agriculture. We report the first comprehensive comparison of the inhibition of urease activity by compounds analysed under the same conditions. Thus, 71 commercially available compounds were screened for their anti-ureolytic properties against both the ureolytic bacterium Klebsiella pneumoniae and purified jack bean urease. Of the tested compounds, 30 showed more than 25% inhibition of the ureolytic activity of Klebsiella pneumoniae or jack bean urease, and among these, carbon disulfide, N-phenylmaleimide, diethylenetriaminepentaacetic acid, sodium pyrrolidinedithiocarbamate, 1,2,4-butanetricarboxylic acid, tannic acid, and gallic acid have not previously been reported to possess anti-ureolytic properties. The diverse effects of metal ion chelators on ureolysis were investigated using a cellular nickel uptake assay. Ethylenediaminetetraacetic acid (EDTA) and dimethylglyoxime (DMG) clearly reduced the nickel import and ureolytic activity of cells, oxalic acid stimulated nickel import but reduced the ureolytic activity of cells, 1,2,4-butanetricarboxylic acid strongly stimulated nickel import and slightly increased the ureolytic activity of cells, while L-cysteine had no effect on nickel import but efficiently reduced the ureolytic activity of cells.

Inhibition studies of Helicobacter pylori urease with Schiff base copper(ii) complexes

Nine new copper(ii) complexes derived from various Schiff bases were prepared. Five complexes show effective urease inhibitory activities. Complex5has the most effective activity against urease, with a mixed competitive inhibition mechanism.

Physico-chemical Analysis, Microbial Isolation, Sensitivity Test of the Isolates and Solar Disinfection of Water Running in Community Taps and River Kandutura in Nakuru North Sub-county, Kenya

Nakuru North sub-county is a peri-urban area which has both dry and wet seasons. Its residents rely mostly on untreated water sources for daily water needs due to unreliable water supply from the urban council. However, this water has not been evaluated on its quality despite residents solely depending on it. This study was aimed at determining the physico-chemical and bacteriological quality of water drawn from River Kandutura and water taps in Nakuru North sub-county. In addition, the study was aimed at carrying out sensitivity test of the isolates to antibiotics and determining effectiveness of solar disinfection in water treatment. A total of 510 water samples; river (255) and taps (255) were collected and analyzed between January and December 2013. Antimicrobial sensitivity test was carried out using Kirby Bauer disk diffusion test. Out of five hundred and ten (510) samples examined for microorganisms, 36.86 % (188/510) were positive for E. coli, Shigella and Salmonella. Water used by Nakuru North sub-county residents is highly contaminated thus posing public health risk. Solar disinfection experiment indicated a possibility of effective decontamination of water up on exposure to sun light for 3-5 h. E. coli showed the highest resistance (26.3 %) followed by Salmonella (17.4 %) while Shigella showed the least (17.1 %). However, there was no significant deference (p=0.98) in resistance among total coliforms, Total heterotrophic and Salmonella at 0.05 level of significant. There is a need to enforce laws and policies on proper waste disposal as part of water pollution control.

Soybean (Glycine max) urease: significance of sulfhydryl groups in urea catalysis

The soybean urease (urea amidohydrolase; EC 3.5.1.5) was investigated to elucidate the presence of sulfhydryl (-SH) groups and their significance in urea catalysis with the help of various -SH group specific reagents. The native urease incubated with 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) showed exponential increase in the absorbance, thereby revealing the presence of -SH groups. A total of 34 -SH groups per hexamer enzyme molecule were estimated from the absorption studies which represents nearly six -SH groups per subunit. The time-dependent inactivation of urease with DTNB, p-chloromercuribenzoate (p-CMB), N-ethylmaleimide (NEM) and iodoacetamide (IAM) showed biphasic kinetics, where half of the enzyme activity was lost more rapidly than the other half. This study reveals the presence of two categories of "accessible" -SH groups, one category being more reactive than the other. The inactivation of urease by p-CMB was largely reversed on treatment with cysteine, which might be due to unblocking of -SH group by mercaptide exchange reaction. Finally, when NEM inactivated urease was incubated with sodium fluoride, a time-dependent regain of activity was observed with higher concentrations of fluoride ion.