Dependence Of Half-life Research Articles

Predictions of nuclear β -decay half-lives with machine learning and their impact on r -process nucleosynthesis

Nuclear $\beta$ decay is a key process to understand the origin of heavy elements in the universe, while the accuracy is far from satisfactory for the predictions of $\beta$-decay half-lives by nuclear models up to date. In this letter, we pave a novel way to accurately predict $\beta$-decay half-lives with the machine-learning based on the Bayesian neural network, in which the known physics has been explicitly embedded, including the ones described by the Fermi theory of $\beta$ decay, and the dependence of half-lives on pairing correlations and decay energies. The other potential physics, which is not clear or even missing in nuclear models nowadays, will be learned by the Bayesian neural network. The results well reproduce the experimental data with a very high accuracy and further provide reasonable uncertainty evaluations in half-life predictions. These accurate predictions for half-lives with uncertainties are essential for the $r$-process simulations.

Properties of $ \alpha$ -decay to ground and excited states of heavy nuclei

Branching ratios and half-lives of α-decay to the ground-state rotational bands as well as the high-lying excited states of even-even nuclei have been calculated in the framework of the generalized liquid drop model (GLDM) and Royer's formula that we improved very recently. The calculation covers the isotopic chains from Ra to No in the mass regions 222 ≤ A ≤ 252 and 88 ≤ Z ≤ 102. The agreement between the calculated results and the experimental data indicates the reliability of investigating the properties of the unfavored α-decay with our method, especially the improved Royer's formula, which is very valuable for the analysis of experimental data. In addition, the dependence of half-lives on excitation energies of daughter nuclei has been investigated. It is shown that the influence on half-lives becomes stronger and stronger with the increase of the excitation energies.

Engineering of a Bacillus α-Amylase with Improved Thermostability and Calcium Independency

Successful industrial use of amylases requires that they are sufficiently stable and active at application conditions, e.g., at high temperature in starch-liquefaction process. In the present study, site-directed mutagenesis was used to enhance the thermal stability and calcium independency of a mesophilic alpha-amylase from Bacillus megaterium WHO. Mutations (A53S and H58I) were designed at the calcium-binding site based on the sequence alignment. Kinetic and thermostability parameters of the mutants were analyzed and compared with that of the wild type. In the presence of calcium, the affinity of the enzymes (wild type and mutants) toward starch was increased. In comparison to the wild type, calcium ion had more effect on the catalytic efficiency, k (cat)/K (m), and half-life (at 60 degrees C) of A53S mutant. In A53S, the dependence of half-life on calcium concentration showed that the enhanced calcium binding is likely to be responsible for the increased stability. In contrast, calcium-independent mutant (H58I) possessed high thermostability. In addition, thermodynamic parameters of amylolytic reaction exhibited an increase in the activation energy and the entropy of the system. Kinetics of irreversible thermal inactivation suggests that the activation energy increased by 1.4-fold in the most stable variant.

Novozymes has eight new products

We have used laboratory evolution methods to enhance the thermostability and activity of the psychrophilic protease subtilisin S41, with the goal of investigating the mechanisms by which this enzyme can adapt to different selection pressures. A combined strategy of random mutagenesis, saturation mutagenesis and in vitro recombination (DNA shuffling) was used to generate mutant libraries, which were screened to identify enzymes that acquired greater thermostability without sacrificing low-temperature activity. The half-life of seven-amino acid substitution variant 3-2G7 at 60°C is ∼500 times that of wild-type and far surpasses those of homologous mesophilic subtilisins. The dependence of half-life on calcium concentration indicates that enhanced calcium binding is largely responsible for the increased stability. The temperature optimum of the activity of 3-2G7 is shifted upward by ∼10°C. Unlike natural thermophilic enzymes, however, the activity of 3-2G7 at low temperatures was not compromised. The catalytic efficiency, kcat/KM, was enhanced ∼threefold over a wide temperature range (10 to 60°C). The activation energy for catalysis, determined by the temperature dependence of kcat/KM in the range 15 to 35°C, is nearly identical to wild-type and close to half that of its highly similar mesophilic homolog, subtilisin SSII, indicating that the evolved S41 enzyme retained its psychrophilic character in spite of its dramatically increased thermostability. These results demonstrate that it is possible to increase activity at low temperatures and stability at high temperatures simultaneously. The fact that enzymes displaying both properties are not found in nature most likely reflects the effects of evolution, rather than any intrinsic physical-chemical limitations on proteins.

Directed evolution study of temperature adaptation in a psychrophilic enzyme

We have used laboratory evolution methods to enhance the thermostability and activity of the psychrophilic protease subtilisin S41, with the goal of investigating the mechanisms by which this enzyme can adapt to different selection pressures. A combined strategy of random mutagenesis, saturation mutagenesis and in vitro recombination (DNA shuffling) was used to generate mutant libraries, which were screened to identify enzymes that acquired greater thermostability without sacrificing low-temperature activity. The half-life of seven-amino acid substitution variant 3-2G7 at 60°C is ∼500 times that of wild-type and far surpasses those of homologous mesophilic subtilisins. The dependence of half-life on calcium concentration indicates that enhanced calcium binding is largely responsible for the increased stability. The temperature optimum of the activity of 3-2G7 is shifted upward by ∼10°C. Unlike natural thermophilic enzymes, however, the activity of 3-2G7 at low temperatures was not compromised. The catalytic efficiency, kcat/KM, was enhanced ∼threefold over a wide temperature range (10 to 60°C). The activation energy for catalysis, determined by the temperature dependence of kcat/KM in the range 15 to 35°C, is nearly identical to wild-type and close to half that of its highly similar mesophilic homolog, subtilisin SSII, indicating that the evolved S41 enzyme retained its psychrophilic character in spite of its dramatically increased thermostability. These results demonstrate that it is possible to increase activity at low temperatures and stability at high temperatures simultaneously. The fact that enzymes displaying both properties are not found in nature most likely reflects the effects of evolution, rather than any intrinsic physical-chemical limitations on proteins.