Direct Genetic and Enzymatic Evidence for Oxidative Cyclization in Hygromycin B Biosynthesis

Hygromycin B is an aminoglycoside antibiotic with a structurally distinctive orthoester linkage. Despite its long history of use in industry and in the laboratory, its biosynthesis remains poorly understood. We show here, by in-frame gene deletion <i>in vivo</i> and detailed enzyme characterization <i>in vitro</i>, that formation of the unique orthoester moiety is catalyzed by the α-ketoglutarate- and non-heme iron-dependent oxygenase HygX. In addition, we identify HygF as a glycosyltransferase adding UDP-hexose to 2-deoxystreptamine, HygM as a methyltransferase responsible for N-3 methylation, and HygK as an epimerase. These experimental results and bioinformatic analyses allow a detailed pathway for hygromycin B biosynthesis to be proposed, including the key oxidative cyclization reactions

Highly Selective and Humidity-Resistant Triethylamine Sensors Based on Pt and Cr₂O₃ Nanoparticles

A triethylamine gas sensor with humidity resistance, high selectivity, and high response is designed. Chromium oxide particles were prepared by heating them in a water bath at 80 °C. Pt/Cr2O3 nanoparticles were obtained by sodium borohydride reduction. The structure morphology of nanoparticles was characterized by some methods. The gas response test results showed that the modification of Pt improved the response value and selectivity of Cr2O3 to triethylamine. It was found that Cr2O3–2Pt nanoparticles had the best performance, and at the optimum operating temperature of 160 °C, its response value reached 200, 68 times that of Cr2O3 (S = 2.95). In addition, the modification of Pt made Cr2O3–2Pt nanoparticles had a wide range of humidity applications. The mechanism of gas response is explained by using the Schottky barrier and hole accumulation layer model of Pt and Cr2O3 contact and energy band theory