Metabolic discrimination between cholesterol and β-amyrin by Phytophthora cactorum

When cultures of Phytophthora cactorum were incubated on solid medium for 3 weeks in the dark at 20 C with [¹⁴C] cholesterol or [¹⁴C]β-amyrin, the [¹⁴C] cholesterol was assimilated into the advancing mycelium to a greater extent than the [¹⁴C]β-amyrin. Examination of the mycelium and medium for radioactive metabolites showed significant differences in the metabolism of the 2 labeled compounds. Cholesterol was converted mainly to esters and to some extent to glycosides, whereas β-amyrin was only slightly converted to esters and not at all to glycosides.