Economical one-pot synthesis of isoquercetin and D-allulose from quercetin and sucrose using whole-cell biocatalyst.

Isoquercetin and D-allulose have diverse applications and significant value in antioxidant, antibacterial, antiviral, and lipid metabolism. Isoquercetin can be synthesized from quercetin, while D-allulose is converted from D-fructose. However, their production scale and overall quality are relatively low, leading to high production costs. In this study, we have devised a cost-effective one-pot method for biosynthesizing isoquercetin and D-allulose using a whole-cell biocatalyst derived from quercetin and sucrose. To achieve this, the optimized isoquercetin synthase and D-allulose-3-epimerase were initially identified through isofunctional gene screening. In order to reduce the cost of uridine diphosphate glucose (UDPG) during isoquercetin synthesis and ensure a continuous supply of UDPG, sucrose synthase is introduced to enable the self-circulation of UDPG. At the same time, the inclusion of sucrose permease was utilized to successfully facilitate the catalytic production of D-allulose in whole cells. Finally, the recombinant strain BL21/UGT-SUS+DAE-SUP, which overexpresses MiF3GTMUT, GmSUS, EcSUP, and DAEase, was obtained. This strain co-produced 41±2.4 mg/L of isoquercetin and 5.7±0.8 g/L of D-allulose using 120 mg/L of quercetin and 20 g/L of sucrose as substrates for 5 h after optimization. This is the first green synthesis method that can simultaneously produce flavonoid compounds and rare sugars. These findings provide valuable insights and potential for future industrial production, as well as practical applications in factories.

Harnessing the glucosyltransferase activities of Clostridium difficile for functional studies of toxins A and B.

The incidence of Clostridium difficile infection (CDI) has been increasing within the last decade. Pathogenic strains of C. difficile produce toxin A and/or toxin B, which are important virulence factors in the pathogenesis of this bacterium. Current methods for diagnosing CDI are mostly qualitative tests that detect either the bacterium or the toxins. We have developed an assay (Cdifftox activity assay) to detect C. difficile toxin A and B activities that is quantitative and cost-efficient and utilizes a substrate that is stereochemically similar to the native substrate of the toxins (UDP-glucose). To characterize toxin activity, toxins A and B were purified from culture supernatants by ammonium sulfate precipitation and chromatography through DEAE-Sepharose and gel filtration columns. The activities of the final fractions were quantitated using the Cdifftox activity assay and compared to the results of a toxin A- and B-specific enzyme-linked immunosorbent assay (ELISA). The affinity for the substrate was >4-fold higher for toxin B than for toxin A. Moreover, the rate of cleavage of the substrate was 4.3-fold higher for toxin B than for toxin A. The optimum temperature for both toxins ranged from 35 to 40°C at pH 8. Culture supernatants from clinical isolates obtained from the stools of patients suspected to be suffering from CDI were tested using the Cdifftox activity assay, and the results were compared to those of ELISA and PCR amplification of the toxin genes. Our results demonstrate that this new assay is comparable to the current commercial ELISA for detecting the toxins in the samples tested and has the added advantage of quantitating toxin activity.

Assessment of postprandial hepatic glycogen synthesis from uridine diphosphoglucose kinetics in obese and lean non-diabetic subjects.

BACKGROUND: Obese patients are frequently characterized by insulin resistance and decreased insulin-mediated glycogen synthesis in skeletal muscle. Whether they also have impaired postprandial hepatic glycogen synthesis remains unknown. AIM: To determine whether postprandial hepatic glycogen synthesis is decreased in obese patients compared to lean subjects. METHODS: Lean and obese subjects with impaired glucose tolerance were studied over 4h after ingestion of a glucose load. Hepatic uridine diphosphoglucose kinetics were assessed using 13C-galactose infusion, with monitoring of urinary acetaminophen-glucuronide isotopic enrichment to estimate hepatic glycogen kinetics. RESULTS: Estimated net hepatic glycogen synthesis amounted to 18.6 and 22.6% of the ingested load in lean and obese subjects, respectively. CONCLUSION: Postprandial hepatic glycogen metabolism is not impaired in non-diabetic obese subjects.

Uridine diphosphoglucose content of human erythrocytes: assessment by conversion to uridine diphosphoglucuronate.

To settle the ongoing controversy regarding differential uridine diphosphoglucose (UDPG) and uridine diphosphogalactose (UDPGal) content of erythrocytes, which may be important in evaluating the metabolic abnormality in patients with galactosemia, we derived a combined enzymatic-high-performance liquid chromatography (HPLC) assay. Uridine diphosphoglucuronate (UDPGA), the unique product of UDPG dehydrogenase activity, was separated and quantified by HPLC in extracts of human erythrocytes. The quantity of UDPGA produced in cell filtrates incubated with the enzyme corresponds to the amount of UDPG directly determined by HPLC. The amount of UDPGA produced was independent of the enzyme purity or activity used. On the other hand, the amounts of UDPG estimated by fluorometric measurement of the production of reduced nicotinamide adenine dinucleotide varied with the enzyme purity and activity. The combined enzymatic-HPLC method confirms the direct determinations of UDPG content of normal erythrocytes. The results indicate that, under appropriate conditions, the fluorometric-based assay will give accurate estimates of UDPG, but the direct HPLC method yields consistent and correct UDPG and UDPGal determinations.