Total-body dynamic PET/CT imaging reveals kinetic distribution of [13N]NH3 in normal organs.

PURPOSE: To systematically investigate kinetic metrics and metabolic trapping of [13N]NH3 in organs. METHODS: Eleven participants performed total-body [13N]NH3 dynamic positron emission tomography (PET). Regions of interest were drawn in organs to obtain time-to-activity curves (TACs), which were fitted with an irreversible two-tissue compartment model (2TC) to investigate constant rates K1, k2 and k3, and to calculate Ki. Additionally, one-tissue compartment model using full data (1TCfull) and the first four minutes of data (1TC4min) were fitted to TAC data. K1 and k2 were compared among different models to assess [13N]NH3 trapping in organs. RESULTS: Kinetic rates of [13N]NH3 varied significantly among organs. The mean K1 ranged from 0.049 mL/cm3/min in the muscle to 2.936 mL/cm3/min in the kidney. The k2 and k3 were lowest in the liver (0.001 min- 1) and in the pituitary (0.009 min- 1), while highest in the kidney (0.587 min- 1) and in the liver (0.800 min- 1), respectively. The Ki was largest in the myocardium (0.601 ± 0.259 mL/cm3/min) while smallest in the bone marrow (0.028 ± 0.022 mL/cm3/min). Three groups of organs with similar kinetic characteristics were revealed: (1) the thyroid, the lung, the spleen, the pancreas, and the kidney; (2) the liver and the muscle; and (3) the cortex, the white matter, the cerebellum, the pituitary, the parotid, the submandibular gland, the myocardium, the bone, and the bone marrow. Obvious k3 was identified in multiple organs, and significant changes of K1 in multiple organs and k2 in most organs were found between 2TC and 1TCfull, but both K1 and k2 were comparable between 2TC and 1TC4min. CONCLUSION: The kinetic rates of [13N]NH3 differed among organs with some have obvious 13N-anmmonia trapping. The normal distribution of kinetic metrics of 13N-anmmonia in organs can serve as a reference for its potential use in tumor imaging.

Prediction of micropollutant degradation kinetic constant by ultrasonic using machine learning.

A prediction model based on XGBoost is proposed for ultrasonic degradation of micropollutants' kinetic constants. After parameter optimization through iteration, the model achieves Evaluation metrics with R2 and SMAPE reaching 0.99 and 2.06%, respectively. The impact of design parameters on predicting kinetic constants for ultrasound degradation of trace pollutants was assessed using Shapley additive explanations (SHAP). Results indicate that power density and frequency significantly impact the predictive performance. The database was sorted based on power density and frequency values. Subsequently, 800 raw data were split into small databases of 200 each. After confirming that reducing the database size doesn't affect prediction accuracy, ultrasound degradation experiments were conducted for five pollutants, yielding experimental data. A small database with experimental conditions within the numerical range was selected. Data meeting both feature conditions were filtered, resulting in an optimized 60-data group. After incorporating experimental data, a model was trained for prediction. Degradation kinetic constants for experiments (kE) were compared with predicted constants (for 800 data-based model: kP-800 and for 60 data-based model: kP-60). Results showed ibuprofen, bisphenol A, carbamazepine, and 17ß-Estradiol performed better on the 60-data group (kP-60/kE: 1.00, 0.99, 1.00, 1.00), while caffeine suited the model trained on the 800-data group (kP-800/kE: 1.02).

Oscillatory work and the step that generates force in single myofibrils from rabbit psoas.

The elementary molecular step that generates force by cross-bridges (CBs) in active muscles has been under intense investigation in the field of muscle biophysics. It is known that an increase in the phosphate (Pi) concentration diminishes isometric force in active fibers, indicating a tight coupling between the force generation step and the Pi release step. The question asked here is whether the force generation occurs before Pi release or after release. We investigated the effect of Pi on oscillatory work production in single myofibrils and found that Pi-attached state(s) to CBs is essential for its production. Oscillatory work is the mechanism that allows an insect to fly by beating its wings, and it also has been observed in skeletal and cardiac muscle fibers, implying that it is an essential feature of all striated muscle types. With our studies, oscillatory work disappears in the absence of Pi in experiments using myofibrils. This suggests that force is generated during a transition between steps of oscillatory work production, and that the states involved in force production must have Pi attached. With sinusoidal analysis, we obtained the kinetic constants around the Pi release steps, established a CB scheme, and evaluated force generated (and supported) by each CB state. Our results demonstrate that force is generated before Pi is released, and the same force is maintained after Pi is released. Stretch activation and/or delayed tension can also be explained with this CB scheme and forms the basis of force generation and oscillatory work production.

Biochemical and thermodynamic properties of de novo synthesized urease from Vicia sativa seeds with enhanced industrial applications.

Urease is one of the most significant enzymes in the industry. The objective of this research was to isolate and partially purify urease from Vicia sativa seeds with urease characterization. With a 6.4 % yield, the purification fold was 9.0. By using chromatography, it was determined that the isolated urease had a molecular weight of 55 kDa. The maximum urease activity was found following a 60-s incubation period at 40 °C and pH 8. The activity of urease was significantly boosted by a mean of calcium, barium, DL-dithiothreitol, Na2EDTA, and citrate (16.9, 26.6, 18.6, 13.6, and 31 %), respectively. But nickel and mercury caused inhibitory effects and completely inhibited urease activity, indicating the presence of a thiol (-SH) group in the enzyme active site. The Arrhenius plot was used to analyze the thermodynamic constants of activation, Ea, ΔH*, ΔG*, and ΔS*. The results showed that the values were 30 kJ/mol, 93.14 kJ/mol, 107.17 kJ/mol/K, and -40.80 J/mol/K, respectively. The significance of urease extraction from various sources may contribute to our understanding of the metabolism of urea in plants. The current report has novelty as it explained for the first time the kinetics and thermodynamics of hydrolysis of urea and inactivation of urease from V. sativa seeds.

Wavelength synergistic effects in continuous flow-through water disinfection systems.

The past decade's development of UV LEDs has fueled significant research in water disinfection, with widespread debate surrounding the potential synergies of multiple UV wavelengths. This study analyses the use of three UV sources (265, 275, and 310 nm) on the inactivation of Escherichia coli bacteria in two water matrixes. At maximum intensity in wastewater, individual inactivation experiments in a single pass set-up (Flow rate = 2 L min-1, Residence time = 0.75 s) confirmed the 265 nm light source to be the most effective (2.2 ± 0.2 log units), while the 310 nm led to the lowest inactivation rate (0.0003 ± 7.03×10-5 log units). When a combination of the three wavelengths was used, an average log reduction of 4.4 ± 0.2 was observed in wastewater. For combinations of 265 and 275 nm, the average log reductions were similar to the sum of individual log reductions. For combinations involving the use of 310 nm, a potential synergistic effect was investigated by the use of robust statistical analysis techniques. It is concluded that combinations of 310 nm with 265 nm or 275 nm devices, in sequential and simultaneous mode, present a significant synergy at both intensities due to the emission spectra of the selected LEDs, ensuring the possibility of two inactivation mechanisms. Finally, the electrical energy per order of inactivation found the three-wavelength combination to be the most energy efficient (0.39 ± 0.05, 0.36 ± 0.01 kWh m-3, at 50% and 100% dose, respectively, in wastewater) among the synergistic combinations.

Molecular modification of β-glucosidase from the midgut of Macrotermes barneyi / 生物工程学报

Cellulose hydrolysis to glucose requires a series of cellulase enzymes, of which β-glucosidases play a crucial role. β-glucosidase (MbmgBG1) derived from the midgut of Macrotermes barneyi has higher glucose tolerance (maintaining more than 60% enzyme activity at 1.5 mol/L glucose). However, low enzyme activity and poor thermal stability limit the applications of β-glucosidase in food industries. Point mutants (F167L, T176C, E347I, R354K, N393G and V425M) were obtained by site-directed mutagenesis of non-conserved amino acids near conserved amino acids. Among them, the specific activities against to substrate pNPG of two mutants (F167L and R354K) were about 2-fold and 4-fold higher than that of MbmgBG1. Kcat/Km values were also higher than that of the wild-type, reflecting stronger affinity to the substrate and higher catalytic ability of mutants than MbmgBG1. When the glucose concentration was 1.5 mol/L, the enzyme activity of MbmgBG1 was about 60% of the original activity. F167L and R354K kept 60% enzymatic activity when the glucose concentrations of was 2.0 mol/L and 3.0 mol/L, respectively. These results lay a foundation for further studies on the catalytic efficiency of β-glucosidase.