A new tool force model to be presented is based upon process geometry and thecharacteristics of the force system, in which the forces acting on the tool rake face, the cuttingedge rounding and the clearance face have ...A new tool force model to be presented is based upon process geometry and thecharacteristics of the force system, in which the forces acting on the tool rake face, the cuttingedge rounding and the clearance face have been considered, and the size effect is accountable forthe new model. It is desired that the model can be well applicable to conventional diamond turningand the model may be employed as a tool in the design of diamond tools. This approach is quitedifferent from traditional investigations primarily based on empirical studies. As the depth of cutbecomes the same order as the rounded cutting edge radius, sliding along the clearance face due toelastic recovery of workpiece material and plowing due to the rounded cutting edge may becomeimportant in micro-machining, the forces acting on the cutting edge rounding and the clearance facecan not be neglected. For this reason, it is very important to understand the influence of someparameters on tool forces and develop a model of the relationship between them.展开更多
Tripterygium hypoglaucum(Levl.)Hutch,a traditional Chinese medicinal herb with a long history of use,is widely distributed in China.One of its main active components,celastrol,has great potential to be developed into ...Tripterygium hypoglaucum(Levl.)Hutch,a traditional Chinese medicinal herb with a long history of use,is widely distributed in China.One of its main active components,celastrol,has great potential to be developed into anti-cancer and anti-obesity drugs.Although it exhibits strong pharmacological activities,there is a lack of sustainable sources of celastrol and its derivatives,making it crucial to develop novel sources of these drugs through synthetic biology.The key step in the biosynthesis of celastrol is considered to be the cyclization of 2,3-oxidosqualene into friedelin under the catalysis of 2,3-oxidosqualene cyclases.Friedelin was speculated to be oxidized into celastrol by cytochrome P450 oxidases(CYP450s).Here,we reported a cytochrome P450 ThCYP712K1 from Tripterygium hypoglaucum(Levl.)Hutch that catalyzed the oxidation of friedelin into polpuonic acid when heterologously expressed in yeast.Through substrate supplementation and in vitro enzyme analysis,ThCYP712K1 was further proven to catalyze the oxidation of friedelin at the C-29 position to produce polpunonic acid,which is considered a vital step in the biosynthesis of celastrol,and will lay a foundation for further analysis of its biosynthetic pathway.展开更多
基金This project is supported by National Natural Science Foundation of China (No.50175022)National Aerospace Support Foundation of China(No.0223HIT07).
文摘A new tool force model to be presented is based upon process geometry and thecharacteristics of the force system, in which the forces acting on the tool rake face, the cuttingedge rounding and the clearance face have been considered, and the size effect is accountable forthe new model. It is desired that the model can be well applicable to conventional diamond turningand the model may be employed as a tool in the design of diamond tools. This approach is quitedifferent from traditional investigations primarily based on empirical studies. As the depth of cutbecomes the same order as the rounded cutting edge radius, sliding along the clearance face due toelastic recovery of workpiece material and plowing due to the rounded cutting edge may becomeimportant in micro-machining, the forces acting on the cutting edge rounding and the clearance facecan not be neglected. For this reason, it is very important to understand the influence of someparameters on tool forces and develop a model of the relationship between them.
基金supported by the National Key R&D Program of China(No.2020YFA0908000)the National Natural Science Foundation of China(Nos.81773830 and 81973418)the Key Project at Central Government Level:the ability establishment of sustainable use for valuable Chinese medicine resources(No.2060302-1806-03),and the National Program for Special Support of Eminent Professionals.
文摘Tripterygium hypoglaucum(Levl.)Hutch,a traditional Chinese medicinal herb with a long history of use,is widely distributed in China.One of its main active components,celastrol,has great potential to be developed into anti-cancer and anti-obesity drugs.Although it exhibits strong pharmacological activities,there is a lack of sustainable sources of celastrol and its derivatives,making it crucial to develop novel sources of these drugs through synthetic biology.The key step in the biosynthesis of celastrol is considered to be the cyclization of 2,3-oxidosqualene into friedelin under the catalysis of 2,3-oxidosqualene cyclases.Friedelin was speculated to be oxidized into celastrol by cytochrome P450 oxidases(CYP450s).Here,we reported a cytochrome P450 ThCYP712K1 from Tripterygium hypoglaucum(Levl.)Hutch that catalyzed the oxidation of friedelin into polpuonic acid when heterologously expressed in yeast.Through substrate supplementation and in vitro enzyme analysis,ThCYP712K1 was further proven to catalyze the oxidation of friedelin at the C-29 position to produce polpunonic acid,which is considered a vital step in the biosynthesis of celastrol,and will lay a foundation for further analysis of its biosynthetic pathway.
