Levels of tropinone-reductase activities influence the spectrum of tropane esters found in transformed root cultures of Datura stramonium L.

The nortropane sulphur analogues 8-thiabicyclo3.2.1] octan-3-one, 8-thiabicyclo3.2.1]octan-3a-ol and 8-thiabicyclo3.2.1]octan-3-ol have been found to have differential effects in vitro on the activities of tropinone reductase I and tropinone reductase II from Datura stramonium L. It has been demonstrated that only tropinone reductase I is able to metabolise 8-thiabicyclo3.2.1]octan-3-one and that only this enzyme is inhibited by 8-thiabicyclo3.2.1]octan-3-ol and 8-thiabicyclo3.2.1]octan-3-ol. A K _m of 0.035 mM was determined for 8-thiabicyclo3.2.1]octan-3-one and I₅₀ values of 0.081 mM and 0.021 mM for 8-thiabicyclo3.2.1]octan-3-ol and 8-thiabicyclo3.2.1]octan-3-ol, respectively. The influence that these differential interactions might have on metabolism was investigated in transformed root cultures of D. stramonium. It was found that when these cultures were grown in the presence of either 8-thiabicyclo3.2.1]octan-3-one or 8-thiabicyclo3.2.1]octan-3-ol the spectrum of alkaloids that accumulated was altered from that found in control roots in the manner predicted from the observed effects of these inhibitors on the isolated reductases. The effect could be mimicked by feeding pseudotropine, the product of tropinone reductase II. It is concluded that the relative levels of activity of the two tropinone reductases might play an important role in regulating the balance of tropan-3-ols to tropan-3-ols seen in the spectrum of tropane-alkaloid-producing plants.Abbreviations GC/MS gas chromatography/mass spectrometry; - I₅₀ concentration of inhibitor required to reduce the rate of reaction to half the maximal value; - -TBOL 8-thiabicyclo3.2.1]octan-3-ol; - -TBOL 8-thiabicyclo3.2.1]octan-3-ol; - TBON 8-thiabicyclo3.2.1]octan-3-one; - TR tropinone reductase We are most grateful to J. Eagles (I.F.R., Norwich) for GC/MS analysis, to colleagues at I.P.B.P. and I.F.R. for helpful discussions, to the technical staff (Chemistry, Glasgow) and to W. Millar (Chemistry, Glasgow) for assistance with the reduction of TBON. This work was, in part, supported by a grant to B Dräger from the Deutsche Forschungsgemeinschaft (Dr227/I-I). The research reported here was supported by an Academic Research Collaboration Cooperative Award (project No. 215) from the British Council and the Deutscher Akademischer Austauschdienst to R.J. Robins and B. Dräger.