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Ion effects on 11α-hydroxylation of progesterone and 5α-reduction of 11α-hydroxyprogesterone by Rhizopus nigricans were investigated. Metal ions such as Cu^(2+), Cd^(2+), Co^(2+), Mn^(2+), Zn^(2+), Fe^(2+), Mg^(2+), Fe^(3+) and Na^+ reduced the 11α-hydroxylation activity, while K^+ stimulated the same reaction. Enzyme activity for the 5α-reduction of 11α-hydroxyprogesterone was increased in the presence of Fe^(2+), Mn^(2+), Mg^(2+), Co^(2+), Zn^(2+), Fe^(3+), K^+ and Na^+, whereas it was decreased in the presence of Cd^(2+) and Cu^(2+). Potassium ion of 10^(-3) M of concentration was found to be effective for the promotion of 11α-hydroxylation. On the other hand, cadmium ion of 10^(-4) M was proved to suppress the 5α-reduction reaction. Progesterone is reported to be transformed into 11α-hydroxyprogesterone which, in turn, is converted further into 11α-hydroxy-allopregnane-3, 20-dione by R. nigricans. From this point of view, the highest yield of 11α-hydroxyprogesterone could be obtained when potassium ion of 10^(-3) M was given initially followed by addition of cadmium ion of 10^(-4) M to limit conversion of 11α-hydroxyprogesterone into 11α-hydroxy-allopregnane-3, 20-dione.
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