Analysis of the Catalytic Mechanism of Bifunctional Triterpene/Sesquarterpene Cyclase: Tyr167 Functions To Terminate Cyclization of Squalene at the Bicyclic Step.

Onoceroids are a group of triterpenes biosynthesized from squalene or dioxidosqualene by cyclization from both termini. We previously identified a bifunctional triterpene/sesquarterpene cyclase (TC) that constructs a tetracyclic scaffold from tetraprenyl-ß-curcumene (C35 ) but a bicyclic scaffold from squalene (C30 ) in the first reaction. TC also accepts the bicyclic intermediate as a substrate and generates tetracyclic and pentacyclic onoceroids in the second reaction. In this study, we analyzed the catalytic mechanism of an onoceroid synthase by using mutated enzymes. TCY167A produced an unnatural tricyclic triterpenol, but TCY167L , TCY167F , and TCY167W formed small quantities of tricyclic compounds, which suggested that the bulk size at Y167 contributed to termination of the cyclization of squalene at the bicyclic step. Our findings provide insight into the unique catalytic mechanism of TC, which triggers different cyclization modes depending on the substrate. These findings may facilitate the large-scale production of an onoceroid for which natural sources are limited.

Early effects of oral administration of esomeprazole and omeprazole on the intragastric pH.

BACKGROUND/AIMS: The aim of our study was to investigate the inhibitory effects on gastric acid secretion of a single oral dose of a proton pump inhibitor, esomeprazole 20 mg and omeprazole 20 mg. METHODOLOGY: A total of 14 Helicobacter pylori-negative male subjects participated in this study. Intragastric pH was monitored continuously for 6 hours after a single oral dose of omeprazole 20 mg and a single oral dose of esomeprazole 20 mg. Each administration was separated by a 7-day washout period. RESULTS: During the 6-hour study period, the average pH after administration of esomeprazole was higher than that after the administration of omeprazole. Also during the 6-hour study period, each of pH > 2, 3, 3.5, 4, and 5 was maintained for a longer duration after administration of esomeprazole 20 mg than after administration of omeprazole 20 mg (median: 75.4% vs. 53.8%, p = 0.0138; 52.1% vs. 33.4%, p = 0.0188; 45.8% vs. 28.2%, p = 0.0262; 42.5% vs. 20.7%, p = 0.0414; 35.8% vs. 11.6%, p = 0.0262; respectively). CONCLUSIONS: In Helicobacter pylori-negative healthy male subjects, single oral administration of esomeprazole 20 mg increased the intragastric pH more rapidly than single oral administration of omeprazole 20 mg.

Construction of an artificial system for ambrein biosynthesis and investigation of some biological activities of ambrein.

Ambergris, a sperm whale metabolite, has long been used as a fragrance and traditional medication, but it is now rarely available. The odor components of ambergris result from the photooxidative degradation of the major component, ambrein. The pharmacological activities of ambergris have also been attributed to ambrein. However, efficient production of ambrein and odor compounds has not been achieved. Here, we constructed a system for the synthesis of ambrein and odor components. First, we created a new triterpene synthase, "ambrein synthase," for mass production of ambrein by redesigning a bacterial enzyme. The ambrein yields were approximately 20 times greater than those reported previously. Next, an efficient photooxidative conversion system from ambrein to a range of volatiles of ambergris was established. The yield of volatiles was 8-15%. Finally, two biological activities, promotion of osteoclast differentiation and prevention of amyloid ß-induced apoptosis, were discovered using the synthesized ambrein.