pH-Dependent reactivity for glycyl-L-tyrosine in carboxypeptidase-A-catalyzed hydrolysis

Identification of blood-red color formation in edible bird's nests provides a new strategy for safety control

In order to reveal the color formation mechanism of blood-red edible bird's nests (EBNs) and develop a quick and specific strategy to distinguish the artificial fake one, multiple methods of UPLC-TOF/MS, UV, NMR, FT-IR and 2D IR were used to detect the chemical markers of the reddening reaction, the results showed that the reddening substances were C₉H₁₀N₂O₅ and C₉H₉NO₆, which were verified as products of a phenol-keto tautomerism evolved from l-tyrosine. Moreover, natural and artificial red EBNs with varying degrees of chemical fumigation also can be successfully distinguished using the chemical markers, and the protein variation in SDS-PAGE gel could also support the distinction. This work established a systematic method of chemical identification for both natural and artificial blood-red EBNs, and provided a new identification strategy for food safety control that can promote the development of a healthier market of EBNs.

QM/MM simulations of amyloid-β 42 degradation by IDE in the presence and absence of ATP

The ability of the insulin-degrading enzyme (IDE) to degrade amyloid-β 42 (Aβ42), a process regulated by ATP, has been studied as an alternative path in the development of drugs against Alzheimer's disease. In this study, we calculated the potential of mean force for the degradation of Aβ42 by IDE in the presence and absence of ATP by umbrella sampling with hybrid quantum mechanics and molecular mechanics (QM/MM) calculations, using the SCC-DFTB QM Hamiltonian and Amber ff99SB force field. Results indicate that the reaction occurs in two steps: The first step is characterized by the formation of the intermediate. The second step is characterized by breaking the peptide bond of the substrate, the latter being the rate-determining step. In our simulations, the activation energy barrier in the absence of ATP is 15 ± 2 kcal mol(-1), which is 7 kcal mol(-1) lower than in the presence of ATP, indicating that the presence of the nucleotide decreases the reaction rate by about 10(5) times.