(S)-4-Acetamido-5-hydroxypentanoic acid

MPO-derived oxidants including HOCl contribute to tissue damage and the initiation and propagation of inflammatory diseases. The search for small molecule inhibitors of myeloperoxidase, as molecular tools and potential drugs, requires the application of high throughput screening assays based on monitoring the activity of myeloperoxidase. In this study, we have compared three classes of fluorescent probes for monitoring myeloperoxidase-derived hypochlorous acid, including boronate-, aminophenyl- and thiol-based fluorogenic probes and we show that all three classes of probes are suitable for this purpose. However, probes based on the coumarin fluorophore turned out to be not reliable indicators of the inhibitors' potency. We have also determined the rate constants of the reaction between HOCl and the probes and they are equal to 1.8 × 104 M-1s-1 for coumarin boronic acid (CBA), 1.1 × 104 M-1s-1 for fluorescein based boronic acid (FLBA), 3.1 × 104 M-1s-1 for 7-(p-aminophenyl)-coumarin (APC), 1.6 × 104 M-1s-1 for 3'-(p-aminophenyl)-fluorescein (APF), and 1 × 107 M-1s-1 for 4-thiomorpholino-7-nitrobenz-2-oxa-1,3-diazole (NBD-TM). The high reaction rate constant of NBD-TM with HOCl makes this probe the most reliable tool to monitor HOCl formation in the presence of compounds showing HOCl-scavenging activity.

Co-invasion by two invasive plant species (IPS) can occur in the same habitat. Diversified acid deposition may change the co-invasion process by altering litter decomposition and plant-soil feedback signalling. This study examined the co-decomposition of two Asteraceae IPS (Solidago canadensis L. and Bidens pilosa L.) on litter decomposition rate, soil enzyme activities, and soil N-fixing bacterial communities under diversified acid deposition (mixed acid deposition at pH 5.6 and at pH 4.5, sulfuric acid at pH 4.5, and nitric acid at pH 4.5). B. pilosa litter degraded faster than S. canadensis litter. Acid deposition at higher acidity accelerated the decomposition rate of both pure S. canadensis litter and the equally mixed litters from the two Asteraceae IPS. Antagonistic responses may occur during the co-decomposition of the two Asteraceae IPS with mixed acid deposition, regardless of the pH, as well as with nitric acid deposition at pH 4.5; in contrast, there may be neutral responses for the co-decomposition process with sulfuric acid at pH 4.5. The type of acid deposited may be one of the key factors affecting the intensity of the mixing effect affecting the co-decomposition. Acid deposition at higher acidity weakened the antagonistic responses for the co-decomposition of the two Asteraceae IPS compared with the response to weak acids. Together, these results indicate that acid deposition at higher acidity could facilitate the co-invasion of the two Asteraceae IPS mainly through accelerated litter decomposition as well as weakened antagonistic responses for co-decomposition.

The development of the stationary-phase, low-pH-inducible acid tolerance response (ATR) in the Salmonella contaminant of beef during the processing arises food safety concerns, because it may evoke bacterial coping mechanisms against bactericidal insults and alter gene expression that contribute to pathogen virulence. However, information on the development of the ATR and the stability (defined as the capacity to maintain the acquired acid tolerance after induction) in the Salmonella during the production and distribution of beef is limited. After adaptation overnight, ATRs in the 79 strains of Salmonella isolated from beef processing plants were investigated by comparing the log reduction in the 2-h acid challenge trials at pH 3.0. Six representative strains were selected to further estimate the effect of three factors in the incubation period on the development of the ATR, including adapted pH values (5.0, 5.4, 6.0, and 7.0), temperatures (10 °C and 37 °C), and the adaptation media (meat extract and brain heart infusion media). The stability of acid tolerance during the long-time chilled storage (4 °C for 13 days) was also observed on two strains of serotypes S. Derby and S. Meleagridis. All the strains isolated from beef processing plants exhibited an enhanced acid tolerance indicating the widespread existence of ATR. The results also revealed that strain variability was present in the development of ATR. Significant tolerance to lethal acidic environments (pH 3.0) was found when the Salmonella strains had been acid-adapted in meat extract at pH 5.0, pH 5.4, or pH 6.0, which indicated the possible induction of ATR during beef production. After the acid adaptations, the population reduction after the acid challenge (BHI, pH = 3) in the strains was significantly lower than the non-induced at the 1d, 7 day and 13 day's storage in meat extract media at 4 °C, which revealed the persistence of ATR during beef distribution. Compared to 37 °C, adaptation in lower temperature (10 °C) significantly reduced the ATR and no ATR was developed when adapted in 4 °C. This emphasizes the importance of keeping a low temperature of beef throughout the supply chains of beef industry.