Major advances have been made during the last decade in our understanding of adrenal steroid hormone biosynthesis. Two key players in these pathways are the human mitochondrial cytochrome P450 enzymes CYP11B1 and CYP11B2, which catalyze the final steps in the biosynthesis of cortisol and aldosterone. Using data from mutations found in patients suffering from steroid hormonerelated diseases, from mutagenesis studies and from the construction of threedimensional models of these enzymes, structural information could be deduced that provide a clue to the stereo and regiospecific steroid hydroxylation reactions carried out by these enzymes. In this review, we summarize the current knowledge on the physiological function and the biochemistry of these enzymes. Furthermore, the pharmacological and toxicological importance of these steroid hydroxylases, the means for the identification of their potential inhibitors and possible biotechnological applications are discussed.

Purpose: A better understanding of the vitamin D₃ metabolism is required to evaluate its potential therapeutic value for cancers. Here, we set out to contribute to the understanding of vitamin D₃ metabolism in glioblastoma multiforme. Experimental Design: We did nested touchdown reverse transcription-PCR (RT-PCR) to identify CYP27B1 splice variants and real-time RT-PCR to quantify the expression of CYP27B1. A cell line was treated with calcitriol to determine the effect on the expression of CYP27B1, 1α,25-dihydroxyvitamin D₃-24-hydroxylase (CYP24), and vitamin D₃ receptor (VDR). We generated three antibodies for the specific detection of CYP27B1 and splice variants. High-performance TLC was done to determine the endogenous CYP27B1 activity and the functionality of CYP27B1 splice variants. Using WST-1 assay, we determined the effect of vitamin D₃ metabolites on proliferation. Results: We report a total of 16 splice variants of CYP27B1 in glioblastoma multiforme and a different expression of CYP27B1 and variants between glioblastoma multiforme and normal tissues. We found preliminary evidence for enzymatic activity of endogenous CYP27B1 in glioblastoma multiforme cell cultures but not for the functionality of the splice variants. By adding calcitriol, we found a proliferative effect for some cell lines depending on the dose of calcitriol. The administration of calcitriol led to an elevated expression of CYP27B1 and CYP24 but left the expression of the VDR unaltered. Conclusions: Our findings show that glioblastoma multiforme cell lines metabolize calcidiol. In addition, we show various effects mediated by calcitriol. We found a special vitamin D₃ metabolism and mode of action in glioblastoma multiforme that has to be taken into account in future vitamin D₃–related therapies.

Genetically engineered microorganisms are being increasingly used for the industrial production of complicated chemical compounds such as steroids; however, there have been few reports on the use of the fission yeast Schizosaccharomyces pombe for this purpose. We previously have demonstrated that this yeast is a unique host for recombinant expression of human CYP11B2 (aldosterone synthase), and here we report the functional production of human CYP11B1 (steroid 11β-hydroxylase) in S. pombe using our new integration vector pCAD1. In the human adrenal, the mitochondrial cytochrome P450 enzyme CYP11B1 catalyses the conversion of 11-deoxycortisol to cortisol, a key reaction in cortisol biosynthesis that in addition is of fundamental interest for the technical synthesis of glucocorticoids. We observed that the endogenous mitochondrial electron transport system detected previously by us is capable of supplying this enzyme with the reducing equivalents necessary for steroid hydroxylation activity. Under optimised cultivation conditions the transformed yeasts show in vivo the inducible ability to efficiently and reliably convert deoxycortisol to cortisol at an average rate of 201 μM d⁻¹ over a period of 72 h, the highest value published to date for this biotransformation.