We study the phase structure of lattice QCD with heavy quarks at finite
temperature and density by a histogram method. We determine the location of the
critical point at which the first-order deconfining transition in the
heavy-quark limit turns into a crossover at intermediate quark masses through a
change of the shape of the histogram under variation of coupling parameters. We
estimate the effect of the complex phase factor which causes the sign problem
at finite density, and show that, in heavy-quark QCD, the effect is small
around the critical point. We determine the critical surface in 2+1 flavor QCD
in the heavy-quark region at all values of the chemical potential mu including
mu=infty.Comment: 26 pages, 21 figures, 1 tabl
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 β-induced apoptosis, were discovered using the synthesized ambrein.
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-β-curcumene (C ) but a bicyclic scaffold from squalene (C ) 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. TC produced an unnatural tricyclic triterpenol, but TC , TC , and TC 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.
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