The influence of β-cyclodextrin on the kinetics of progesterone transformation by Rhizopus nigricans

The process of progesterone 11 alpha-hydroxylation by the pelleted growth form of the filamentous fungus Rhizopus nigricans has been described with a mathematical model, based on Michaelis-Menten enzyme kinetics and the rate of substrate dissolution. It was confirmed that the low water solubility of steroids is the limiting step of this process at high steroid concentrations. In order to overcome this problem, beta-cyclodextrin, which is known to form inclusion complexes with these organic compounds, was added to the production medium. The phase solubility of the steroid-beta-cyclodextrin system was investigated and the effect of beta-cyclodextrin addition on progesterone biotransformation evaluated. Enhancement of steroid solubility was demonstrated and nearly two-fold increase in reaction rate was found in the presence of beta-cyclodextrin.