Assay of strictosidine synthase from plant cell cultures by high-performance liquid chromatography

An HPLC assay is described for the enzyme strictosidine synthase in which the formation of strictosidine and the decrease of tryptamine can be followed at the same time. In cell cultures of Catharanthus roseus significant amounts of strictosidine glucosidase activity were detected. In crude preparations, the strictosidine synthase reaction is therefore best measured by the secologanin-dependent decrease of tryptamine. In this way, the specific synthase activity in a cell free extract was found to be 56 pkat/mg of protein. Inclusion of 100 mM D(+)-gluconic acid-delta-lactone in the incubation mixture inhibited 75% of the glucosidase activity, without inhibiting the synthase activity. The synthase activity was readily separated from the glucosidase activity by gel filtration on Sephadex G-75 or Ultrogel AcA-44. Cell cultures of Tabernaemontana orientalis did not contain measurable amounts of strictosidine glucosidine activity. The specific strictosidine synthase activity was 130-200 pkat/mg of protein during the growth of this cell culture. Strictosidine synthase is stable at -20 degrees C for at least 2 months.