Involvement of the cell wall ofNocardia restricta on the bioconversions of steroid sapogenins

The bioconversion of tigogenin, (25R)-5-spirostan-3-ol byNocardia restricta to (25R)-4-spirosten-3-one and (25R)-1,4-spirostadien-3-one was strongly increased using protoplasts instead of intact cells. The same effect could be achieved by adding-cyclodextrin to the medium. Since 5-steroid sapogenins pass through the cell wall without hindrance, it can be concluded that the cell wall ofNocardia restricta is a rate-limiting factor only for 5-isomers.