Die Biosynthese cytotoxischer Lignane aus Linum nodiflorum L. (Linaceae): ß-Peltatin 6-O-Methyltransferase

Lignans are widely distributed phenolic compounds in the plant kingdom. Some of them have cytotoxic, antifungal and antimicrobial properties. The aryltetralin lignan podophyllotoxin is used as precursor for semisynthetic derivatives like Etoposide or Teniposide which are used in the treatment of cancer. Podophyllotoxin is isolated from Podophyllum plants but it can be found in different other plant families like Linaceae aswell. Other lignans like ß-peltatin or 6-methoxypodophyllotoxin can be isolated from Linum plants, too. Here the ß-peltatin 6-O-methyltransferase is isolated from Linum nodiflorum. The enzyme is purified and characterised. It is a S-adenosylmethionine (SAM)dependent enzyme that methylates ß-peltatin to ß-peltatin A-methylether. The pH-optimum is at 7.5 in 0.1 M Tris-HCl-buffer, the optimal incubation temperature is at 40 °C. An apparent Km-value of 40 µM for ß-peltatin as substrate and of 15 µM for SAM can be determined. For the purification of the enzyme an anion exchange an an affinity chromatography were used. Genes of different methyltransferases were tried to find by the use of degenerated primers. One methyltransferase could be ligated into the pTrc99a vector. The resulting protein was tested for putative substrates. The natural substrate could not be found so far, even if some substrates, mostly derivatives of caffeic acid, were methylated by the resulting methyltransferase.