SINEFUNGIN INHIBITS CHLOROPHYLL SYNTHESIS BY BLOCKING THE S-ADENOSYL-METHIONINE - MG-PROTOPORPHYRIN-IX O-METHYLTRANSFERASE IN GREENING BARLEY LEAVES

Magnesium protoporphyrin IX O-methyltransferase (EC 2.1.1.11) transfer s the methyl group from S-adenosylmethionine (SAM) to the propanoic ac id side chain on the third pyrrole ring of Mg-protoporphyrin IX in the biosynthetic pathway of chlorophyll. The nucleoside analogue sinefung in from Streptomyces is a potent inhibitor of this enzyme. Chlorophyll synthesis was inhibited when dark-grown barley (Hordeum vulgare) leav es were fed with this antibiotic and illuminated. Mg-protoporphyrin IX accumulated in the sinefungin treated leaves and it is suggested that the inhibition of chlorophyll synthesis is caused mainly by an inhibi tion of Mg-protoporphyrin IX O-methyltransferase.