Gaseous inhibition of the transsulfuration pathway by cystathionine ß-synthase.

The transsulfuration pathway plays a key role in mammals for maintaining the balance between cysteine and homocysteine, whose concentrations are critical in several biochemical processes. Human cystathionine ß-synthase is a heme-containing, pyridoxal 5'-phosphate (PLP)-dependent enzyme found in this pathway. The heme group does not participate directly in catalysis, but has a regulatory function, whereby CO or NO binding inhibits the PLP-dependent reactions. In this study, we explore the detailed structural changes responsible for inhibition using quantum chemical calculations to validate the experimentally observed bonding patterns associated with heme CO and NO binding and molecular dynamics simulations to explore the medium-range structural changes triggered by gas binding and propagating to the PLP active site, which is more than 20 Å distant from the heme group. Our results support a previously proposed mechanical signaling model, whereby the cysteine decoordination associated with gas ligand binding leads to breaking of a hydrogen bond with an arginine residue on a neighbouring helix. In turn, this leads to a shift in position of the helix, and hence also of the PLP cofactor, ultimately disrupting a key hydrogen bond that stabilizes the PLP in its catalytically active form.

Effects of Chlorella vulgaris polysaccharides accumulation on growth characteristics of Trachemys scripta elegans.

The present study investigated the effects of the accumulated polysaccharides in Chlorella vulgaris microalgae on the growth characteristics of Trachemys scripta elegans. Sodium alginate was used to prepare immobilized C. vulgaris, and the antioxidant effects of the accumulated polysaccharides in it were determined using Caenorhabditis elegans as a model. We determined the specific growth rates of T. s. elegans (10 in each group) and their levels of non-specific immune-related indexes (including alkaline phosphatase; total superoxide dismutase; catalase; malondialdehyde). Under optimal culturing conditions, the accumulated polysaccharide content in C. vulgaris reached 32.7% (dry weight). Polysaccharides from C. vulgaris significantly improved the hydrogen peroxide-induced oxidative stress resistance and resulted in the enhancement of stress resistance-related antioxidant enzymes, including total superoxide dismutase and catalase (p < 0.05). The accumulated polysaccharides in C. vulgaris were heteropolysaccharides comprising rhamnose, ribose, arabinose, xylose, 2-deoxy-D-glucose, mannose, glucose, galactose, and glucosamine with a molar ratio of 0.26: 0.62: 0.21: 0.10: 0.08: 0.18: 1.00: 0.42: 0.17. Compared with the control group with common feeds, suspended and immobilized C. vulgaris with higher accumulated polysaccharide levels had a positive effect on the specific growth rate of the T. s. elegans (p < 0.05). Further, the suspended and immobilized C. vulgaris with higher accumulated polysaccharide levels significantly increased serum alkaline phosphatase, total superoxide dismutase and catalase activity (p < 0.05) and decreased serum malondialdehyde levels of T. s. elegans (p < 0.05).

Preparation of Chlorella vulgaris polysaccharides and their antioxidant activity in vitro and in vivo.

In the present study, six different polysaccharides (RFPs, MAPs, UWPs, AEPs, HWPs and CEPs) were extracted from Chlorella vulgaris using repeated freeze-thawing, microwave-assisted-, ultrasonic wave-, alkali-, hot water-, and cellulase-based methods; and antioxidant property assays were performed both in vitro and in vivo. Radical-scavenging capacity (using DPPH, superoxide and hydroxyl radicals) and metal chelating ability were assessed in vitro; Caenorhabditis elegans was used to assess antioxidant effects in vivo. Based on the in vitro screening tests, UWPs exhibited high antioxidant capacity. The UWP yield was 17.1% ±â€¯2.2%; the DPPH-, superoxide-, and hydroxyl radical-scavenging rates were 65.1% ±â€¯2.4%, 61.2% ±â€¯2.7%, and 56.2% ±â€¯2.2%, respectively, and the metal chelating ability was 63.6% ±â€¯2.5% at a concentration of 0.4 mg/mL. UWPs also exhibited high antioxidant activity in vivo. UWPs significantly increased the lifespan of C. elegans under oxidative stress induced by hydrogen peroxide compared with the control group, enhanced stress-resistance-related enzymes, including catalase and superoxide dismutase by 7.29% ±â€¯1.8% and 24.41% ±â€¯4.8%, respectively. The results of the present study indicate that the extraction methods of C. vulgaris polysaccharides were a key factor influencing antioxidant activity.