Biotransformation Of Protopanaxadiol-type Saponins By A Kind Of Oospora Wallr.

Ginseng (Panax ginseng C. A. Meyer, Araliaceae) is used in Asian countries as atraditional medicine. The main pharmacologically active components in ginseng areginsenosides. The rare ginsenosides often have better activities than the major ones.As these rare ginsenosides only have different sugar residues compared with themajor ginsenosides Rb1 and Rb2, we can transform the structure of ginsenosides toprepare rare ginsenosides. Currently, the methods of transforming ginsenosidesmainly contain chemical and biological transformation, and biotransformation isconsidered to be more desirable due to its high specificity and low pollution. In thispaper, 22 kinds of phytopathogenic fungi were checked if they can transform majorginsenoside Rb1, Rb2 and Rc, among them, one fungus was chosen for further study.In the first part of this paper, 22 kinds of fungi were screened to explore theirtransformation ability using proto-panaxadiol type saponins (ppd) Rb1, Rb2 and Rc assubstrates. Among these fungi, only 2 fungi could not transform the substrates. Eightfungi could transform the substrates to Rd, and Rd is the main transformation product.Six fungi converted the substrates to Rd and F2. Six fungi transform the ginsenosidesubstrates to C-K. The fungus with the number of 1.91, which could transform ppdinto C-K with high transformation efficiency, was selected for further study. It wasmorphologically identified as Oospora Wallr.In the second part of this paper, the transformation of Rb1, Rb2 and Rc byOospora Wallr was studied. The transformation pathways of ginsenoside Rb1 andRb2 by this strain were: Rb1â†'Rdâ†'F2â†'C-K; Rb2â†'C-Oâ†'C-Y. The optimumconditions were determined: the time of substrate addition, 12 h; pH, 5.0-6.0;temperature, 45oC. Furthermore, the glycosidases secreted by Oospora Wallr wereextracted and fractionated, yielding a partially purified fraction, GE-Ι. The pathwaysof GE-I transforming Rb1, Rb2 and Rc were: Rb1â†'Rdâ†'F2â†'C-K; Rb2â†'C-Oâ†'C-Yâ†'C-K; Rcâ†'Mbâ†'Mcâ†'C-K. The optimum transformaton conditions weredetermined as following: pH, 5.0; temperature, 45 oC. GE-Ιwas stable at pH 4.0-12.0and 30-70 oC.The experimental results provided useful data for the production of ginsenosideC-K in industry and the foundation for studing the glycosidases tranformingginsenosides.