Abstract
Lysine decarboxylase (LDC) is the key enzyme involved in the first step of quinolizidine alkaloids (QAs) biosynthesis. We have cloned the lysine/ornithine decarboxylase (L/ODC) from alkaloid-containing cultivar of L. angustifolius by using PCR-select-subtraction and 5'/3'-RACE techniques. The purified recombinant protein expressed in E. coli exhibited decarboxylase activities towards both L-ornithine and L-lysine with similar Km value. The decarboxylase activities toward both substrates were competitively inhibited by DFMO, which is a specific inhibitor of ODC. We also characterized L/ODC genes from Sophora flavescens and Echinosophora koreensis which produce QAs. Kinetic study of these two purified recombinant L/ODCs showed the decarboxylase activity toward both substrates with similar Km as same as L/ODC from L. angustifolius. The comparison of the catalytic efficiency (k cat /Km) of these three L/ODCs revealed that the preference for L-ornithine over L-lysine is only 0.5-1.5 times. This is the first report on an L/ODC presumably involved in QAs biosynthesis having almost equal decarboxylase activities towards both L-ornithine and L-lysine from plants.
