Abstract: In this study,the key parameters in the biotransformation process of digitoxin by Aspergillus ochraceus  Rn405 were optimized,including the type of cosolvent, substrate concentration,the type and concentration of metal ions.The optimal biotransformation conditions were as follows:1 mmol/L Mn²⁺ was added into the fermentation medium,the cells was grown at 28 °C on a rotary shaker (180 rpm) for 28 h and then the substrate dissolved in DMSO was added to the final concentration of 100 mg/L,and the biotransformation process lasted for 96 h at the same condition.At this point,the conversion ratio of substrate and the generation ratio of 11α-gitoxigenin were 100% and 25.4%,respectively,which was increased by 33.1% and 14.5% compared with original condition.The effects of the two biotransformation products on the myocardial contractility of bufo and rats were investigated using Smith’s perfusion method and Langendorff perfusion method.The results indicated that the product digitoxigenin had the same impact on myocardial cell shrinkage as the substrate digitoxin,while the influence of another product 11α-hydroxy-dgitoxigenin on myocardial cell shrinkage was enhanced compared with the substrate digitoxin and the product digitoxigenin.

Key words: Aspergillus ochraceus, digitoxin, microbial transformation, process optimization, activity analysis