Microorganisms able to bioconvert DL-2-amino-Δ(2)-thiazoline-4-carboxylic acid (DL-ATC) into L-cysteine were originally isolated from 10 soil samples with DL-ATC as the sole nitrogen source. Ninety-seven L-cysteine-producing bacterial strains were screened out and obtained in pure culture. Among them, a strain, designated as HUT-78, was selected as the best producer, with a molar bioconversion rate of 60%. Based on the 16S rRNA gene sequence analysis, this isolate was placed within the genus Pseudomonas. A novel mutant of this strain with a significantly reduced activity of L-cysteine desulfhydrase, a L-cysteine-decomposing enzyme, was derived by UV-mutagenesis. This mutant, designated as mHUT-78, exhibited a 42% increase in L-cysteine producing activity. Moreover, the bioconversion reactions in both the parent and the mutant strain were significantly accelerated by co-overexpression of the two key enzymes, AtcB and AtcC, involved in the bioconversion reaction. 相似文献
The instability of liposomal delivery system during passaging through the gastrointestinal tract (GIT) stimulates a demand to find a stable liposome. This research studied the implications of different types of phospholipids (different fatty acid chain length and saturation, various head group) on liposomal physiochemical properties and stability in the human GIT. The micropolarity of liposomal membrane increased with the decrease of chain lengths of phospholipids, while the morphology observation revealed that the liposomes formed by different phospholipids showed similar in appearance and shapes. The liposomes formed by C20:0 deformed more severely in simulated gastric fluid, while others exhibited slight changes in the membrane structure. In simulated intestinal fluid, pancreatic lipase and phospholipase A2, synergized with bile salts, damaged the bilayers structure of all liposomes, with the entrapped lactoferrin release and hydrolysis. Although the various phospholipid structures lead to some difference on the physicochemical properties (size and micropolarity), the enzymic influence displayed more significance during in vitro digestion compared to the types of wall materials. Current results could provide valuable information for the development of more stable and reliable food-grade liposomes in the GIT.
Mitophagy is an essential process for mitochondrial quality control and turnover. It is activated by two distinct pathways, one dependent on ubiquitin and the other dependent on receptors including FUNDC1. It is not clear whether these pathways coordinate to mediate mitophagy in response to stresses, or how mitophagy receptors sense stress signals to activate mitophagy. We find that the mitochondrial E3 ligase MARCH5, but not Parkin, plays a role in regulating hypoxia‐induced mitophagy by ubiquitylating and degrading FUNDC1. MARCH5 directly interacts with FUNDC1 to mediate its ubiquitylation at lysine 119 for subsequent degradation. Degradation of FUNDC1 by MARCH5 expression desensitizes mitochondria to hypoxia‐induced mitophagy, whereas knockdown of endogenous MARCH5 significantly inhibits FUNDC1 degradation and enhances mitochondrial sensitivity toward mitophagy‐inducing stresses. Our findings reveal a feedback regulatory mechanism to control the protein levels of a mitochondrial receptor to fine‐tune mitochondrial quality. 相似文献