Sterol Delta8-Delta7 isomerases (SIs) catalyze the shift of the double bond from C8-9 to C7-8 in the B-ring of sterols. Surprisingly, the isoenzymes in fungi (ERG2p) and vertebrates [emopamil binding protein (EBP)] are structurally completely unrelated, whereas the sigma1 receptor, a mammalian protein of unknown function, bears significant similarity with the yeast ERG2p. Here, we compare the drug binding properties of SIs and related proteins with [3H]ifenprodil as a common high affinity radioligand (Kd = 1.4-19 nM), demonstrating an intimate pharmacological relationship among ERG2p, sigma1 receptor, and EBP. This renders SIs a remarkable example for structurally diverse enzymes with similar pharmacological profiles and the propensity to bind drugs from different chemical groups with high affinity. We identified a variety of experimental drugs with nanomolar affinity for the human EBP (Ki = 0.5-14 nM) such as MDL28815, AY9944, triparanol, and U18666A. These compounds, as well as the fungicide tridemorph and the clinically used drugs tamoxifen, clomiphene, amiodarone, and opipramol, inhibit the in vitro activity of the recombinant human EBP (IC50 = 0.015-54 microM). The high affinity of the human EBP for 3H-tamoxifen (Kd = 3 +/- 2 nM) implies that the EBP carries the previously described microsomal antiestrogen binding site. Interactions of the EBP with structurally diverse lipophilic amines suggest that novel compounds of related structure should be counterscreened for inhibition of the enzyme to avoid interference with sterol Delta8-Delta7 isomerization.

The yeast gene ERG2 encodes a sterol C8-C7 isomerase and is essential for ergosterol synthesis and cell proliferation. Its striking homology with the so-called sigma1 receptor of guinea pig brain, a polyvalent steroid and drug binding protein, suggested that the yeast sterol C8-C7 isomerase (ERG2) carries a similar high affinity drug binding domain. Indeed the sigma ligands [3H]haloperidol (Kd = 0.3 nM) and [3H]ifenprodil (Kd = 1.4 nM) bound to a single population of sites in ERG2 wild type yeast microsomes (Bmax values of 77 and 61 pmol/mg of protein, respectively), whereas binding activity was absent in strains carrying ERG2 gene mutations or disruptions. [3H]Ifenprodil binding was inhibited by sterol isomerase inhibitors such as fenpropimorph (Ki = 0.05 nM), tridemorph (Ki = 0.09 nM), MDL28,815 (Ki = 0.44 nM), triparanol (Ki = 1.5 nM), and AY-9944 (Ki = 5.8 nM). [3H]Haloperidol specifically photoaffinity-labeled a protein with an apparent molecular weight of 27400, in agreement with the molecular mass of the sterol C8-C7 isomerase (24900 Da). 9E10 c-myc antibodies specifically immunoprecipitated the c-myc tagged protein after [3H]haloperidol photolabeling, unequivocally proving that the drug binding site is localized on the ERG2 gene product. Haloperidol, trifluperidol, and ifenprodil inhibited the growth of Saccharomyces cerevisiae and reduced the ergosterol content of cells grown in their presence. Our results demonstrate that the yeast sterol C8-C7 isomerase has a polyvalent high-affinity drug binding site similar to mammalian sigma receptors and that in yeast sigma ligands inhibit sterol biosynthesis.

There is a myriad of proposals for nasal defect closure. One of the older concepts, the so-called topographical concept, adheres to the nasal subunit principle without taking into consideration textural details of the nasal skin such as thickness and mobility. In a newer concept, a morphological concept, the texture of the nasal skin is a basic consideration for defect closure. The morphological or textural concept demands defect closures only with local flaps of nearly identical texture located within the "unit" nose. In order to find out how the morphological concept influenced our operative design, we carried out a retrospective study from 1988 to 1995 checking the defect closure of all basal cell carcinoma on the nose. Of 598 basal cell carcinoma operated in the face, 141 were located on the nose. During the first years, free skin grafts and regional flaps dominated our operative design, in recent years the use of local flaps according to the criteria of the morphological concept increased significantly, leading not only to functional but also to more aesthetic results.