Hyoscyamine 6/9-hydroxylase

Tropane alkaloids Hyoscyamine 6/3-hydroxylase Hyoscyamus niger Atropa belladonna... 

Matsuda, J., Okabe, S., Hashimoto, T. and Yamada, Y. 1991. Molecular cloning of hyoscyamine 6(3-hydroxylase, a 2-oxyglutarate dependent dioxygenase, from cultured roots of Hyoscyamus niger. Journal of Biological Chemistry, 266 9460-9464. 

Hashimoto, T. and Yamada, Y. 1987. Purification and characterization of hyoscyamine 6(3-hydrolase from root cultures of Hyoscyamus niger L. Hydroxylase and epoxidase activities in the preparation. European Journal of Biochemistry, 164 277-285. 

HASHIMOTO, T., HAYASHI, A., AMANO, Y, KOHNO, J., IWANARI, H., USUDA, S., YAMADA, Y., Hyoscyamine 6P-hydroxylase, an enzyme involved in tropane alkaloid biosynthesis, is localized at the pericycle of the root. J. Biol. Chem., 1991,266, 4648-4653. 

SUZUKI, K., YUN, D.-J., CHEN, X.Y., YAMADA, Y., HASHIMOTO, T., An Atropa belladonna hyoscyamine 6-P-hydroxylase gene is differentially expressed in the root pericycle and anthers. Plant Mol. Biol, 1999, 40, 141-152. 

Important for the production of scopolamine, hyoscyamine 6p-hydroxylase was the first enzyme of tropane alkaloid metabolism to be purified and remains the most rigorously studied. It was obtained in pure form from H. niger root cultures and the preparation showed that it is a bifunctional enzyme with activity both as the 7(3-hydroxylase and as the 6,7 3-epoxidase. A clone for H6H was obtained following the purification of enzyme activity. The gene shows some similarity to other hydroxylases, including those involved in oxidative reactions in the formation of ethylene and anthocyanins (Hashimoto and Yamada, 1994). 

Kanegae, T., Kajiya, H., Amano, Y., Hashimoto, T. and Yamada, Y. (1994) Species-dependent expression of the hyoscyamine 6p-hydroxylase gene in the pericycle. Plant Physiol, 105, 483-90. 

Yamada Y, Hashimoto T. Substrate specihcity of the hyoscyamine 6 3-hydroxylase from cultured roots of Hyoscya-mus niger. Proc. Japan Acad. B 1989 65 156-159. 

Both alkaloids have (+) and (-) forms but only the (-) hyoscyamine and (-) scopolamine are active. The biosynthetic pathway of tropane alkaloids, Fig. (1) is not totally understood, especially at the enzymatic level. Edward Leete has pioneered the biosynthetic studies of tropane alkaloid since 1950"s using whole plants and isotope labels [85-86]. The tropane alkaloid hyoscyamine is bioconverted by the enzyme H6H (hyoscyamine 6p-hydroxylase, EC 1.14.11.11) to scopolamine via 6p-hydroxyhyoscyamine. Hyoscyamine is the ester of tropine and (S)-tropic acid. The (S)-tropic acid moiety derives from the amino acid L-phenylalanine, while the bicyclic tropane ring derives from L-omithine primarily or L-arginine via tropinone. Tropinone is stereospecifically reduced to form either, tropine which is incorporated into hyoscyamine, or on the other hand into pseudotropine which proceeds to calystegines, a group of nortropane derivates that were first found in the Convolvulaceae family [87]. 

F. (1). Tropane alkaloids biosynthetic pathway. The known enzymes are indicated. ODC (ornithine decarboxylase), ADC (arginine decarboxylase), PMT (putrescine methyl transferase), MPO (methyl putrescine oxidase), TRI, TRII (tropinone reductase I, II), H6H (hyoscyamine 6p hydroxylase). 

Tropane alkaloids Hyoscyamine 6 -hydroxylase Hyoscyamus niger... 

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