Journal
PLANTA
Volume 214, Issue 2, Pages 288-294Publisher
SPRINGER
DOI: 10.1007/s004250100617
Keywords
cell culture (Linum); cytochrome P450; lignan; Linum (lignan biosynthesis); podophyllotoxin
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Cell-suspension cultures of Linum flavum L. (Linaceae) synthesize and accumulate aryltetrallydronaphthalene lignans with 6-methoxypodophyllotoxin as the main component. The experimental data indicate that the biosynthesis of 6-methoxypodophyllotoxin occurs via deoxypodophyllotoxin, beta-peltatin, and beta-peltatin-A methyl ether. The enzyme catalyzing the introduction of the hydroxyl group in position 6 is deoxypodophyllotoxin 6-hydroxylase (DOP6H). The enzyme was shown to be a cytochrome P450-dependent monooxygenase by blue-light reversion of carbon monoxide inhibition and inhibition by cytochrome c. DOP6H is a membrane-bound microsomal enzyme with a pH optimum of 7.6 and a temperature optimum of 26 degreesC. Deoxypodophyllotoxin is specifically accepted with an apparent K-m of 20 mum and a saturation concentration of 200 muM; 4'-demethyldeoxypodophyllotoxin is the only other tested substrate accepted for hydroxylation. DOP6H predominantly accepts NADPH as electron donor; NADH can only sustain low hydroxylation activities. A synergistic effect of NADPH and NADH is not observed. The enzyme is saturated around 250 M NADPH; the apparent K-m for this substrate is 36 M.
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