RESUMO
The formation of progesterone hydroxylases by Aspergillus niger 173 was investigated. The constitution of the fermentation medium influenced both the yield and the type of enzymes catalyzing the transformation of progesterone. The enzyme yield also varied with the pH value at which induction was performed as well as with the buffer used. The transformation activity of progesterone was more pronounced with mycelia induced in citrate-phosphate than in phosphate buffer. The results demonstrated that induction of 6beta-hydroxylase was favoured at pH values near neutrality while that of 11alpha-hydroxylase in the presence of citrate ions. The transformation activity of progesterone was optimal at pH 5.0. The action of 11alpha-hydroxylase was also optimal at pH 5.0, but other hydroxylase showed pH optima between 2.2 and 4.0. Progesterone concentrations higher than 6 mg in 50 ml reaction mixture was a limiting factor for the rate of transformation activity.