Estimation of Lipoyllysine Content in Meat and Its Antioxidative Capacity

Depletion of L-Methionine in Foods with an Engineered Thermophilic Methionine γ-lyase Efficiently Inhibits Tumor Growth

Dietary restriction of l-methionine, an essential amino acid, exerts potent antitumor effects on l-methionine-dependent cancers. However, dietary restriction of l-methionine has not been practical for human therapy because of the problem with the administration of l-methionine concentration in foods. Here, a thermophilic methionine γ-lyase (MGL), that catalyzes the cleavage of the C-S bond in l-methionine to produce α-ketobutyric acid, methanethiol, and ammonia was engineered from human cystathionine γ-lyase and almost completely depleted l-methionine at 65 °C, a temperature that accelerates the volatilization of methanethiol and its oxidation products. The high efficiency of l-methionine lysis may be attributed to the cooperative fluctuation and moderate the structural rigidity of 4 monomers in the thermophilic MGL, which facilitates l-methionine access to the entrance of the active site. Experimental diets treated with thermophilic MGL markedly inhibited prostate tumor growth in mice, and in parallel, the in vivo concentrations of l-methionine, its transformation product l-cysteine, and the oxidative stress indicator malondialdehyde significantly decreased. These findings provide a technology for the depletion of l-methionine in foods with an engineered thermophilic MGL, which efficiently inhibits tumor growth in mice.

New insights into exogenous N-acyl-homoserine lactone manipulation in biological nitrogen removal system against ZnO nanoparticle shock

The effects and mechanisms of three N-acyl-homoserine lactones (AHLs) (C₄-HSL, C₆-HSL, and C₁₀-HSL) on responses of biological nitrogen removal (BNR) systems to zinc oxide nanoparticle (NP) shock were investigated. All three AHLs improved the NP-impaired ammonia oxidation rates by up to 50.0 % but inhibited the denitrification process via regulating nitrogen metabolism-related enzyme activities. C₄-HSL accelerated the catalase activity by 13.2 %, while C₆-HSL and C₁₀-HSL promoted the superoxide dismutase activity by 26.6 % and 18.4 %, respectively, to reduce reactive oxygen species levels. Besides, the enhancements of tryptophan protein and humic acid levels in tightly-bound extracellular polymeric substance by AHLs were vital for NP toxicity attenuation. The metabonomic analysis demonstrated that all three AHLs up-regulated the levels of lipid- and antioxidation-related metabolites to advance the system's resistance to NP shock. The "dual character" of AHLs emphasized the concernment of legitimately employing AHLs to alleviate NP stress for BNR systems.