ENZYMATIC PRENYLATION OF ISOFLAVONES IN WHITE LUPIN

Microsomal preparations of white lupin (Lupinus albus) radicles and cell suspension cultures catalyse the prenylation of positions 6, 8 and 3' of the isoflavones genistein and 2'-hydroxygenistein. Both the substrates and the enzyme reaction products are natural constituents of lupin tissues. Enzymatic prenylation of isoflavones required dimethylallyl pyrophosphate (DMAPP) and 12 mM Mn2+ with optimum activity at pH 7.5 in Tris-HCl buffer. The apparent K(m) values for DMAPP and the prenyl acceptors were 4 and 5 muM, respectively. Isopentenyl pyrophosphate was a competitive inhibitor of the prenylation reaction, with an apparent K(i) of 5 muM. The bulk of enzymatic activity was associated with the membrane fraction and could only be solubilized in the presence of a detergent. The differences observed in prenyltransferase activity ratios, in relation to the source of the enzyme and the type of detergent used, suggest that prenylation at positions 6, 8 and 3' of isoflavones is catalysed by a number of distinct enzymes.