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Enzymatic Synthesis of Quinolizidine Alkaloids in Lupin Chloroplasts

Abstract The enzymatic sequence responsible for the biosynthesis of tetracyclic quinolizidine alkaloids could be localized in chloroplasts isolated from Lupinus polyphyllus leaves and L. albus seedlings by differential centrifugation. Upon feeding of cadaverine to isolated chloroplasts lupanine is produced as the main alkaloid. Chloroplasts treated with digitonine produce sparteine and 17-oxosparteine instead of lupanine, thus indicating that the biosynthetic sequence is interrupted. The intermediacy of 17-oxosparteine could be confirmed since exogeneous 17-oxosparteine is converted into lupanine by intact chloroplasts. 17-Oxosparteine synthase (see Z. Naturforsch. 34 c, 704 1979) the key enzyme of quinolizidine alkaloid biosynthesis could be solubilized from chloro plasts treated with detergents or osmotic shock.