Site of Action of Growth Inhibitory Tryptophan Analogues in Catharanthus roseus Cell Suspension Cultures

Fourteen tryptophan analogues have been characterized w ith regard to th e ir grow th inh ib ito ry effects on Catharanthus roseus cell cultures, their inh ib ito ry effect on an th ran ila te synthetase, their incorporation into protein and their substrate affin ity to try p to p h an decarboxylase. The toxicity of 12 o f the analogues was directly correlated w ith th e ir inh ib ito ry effect on an th ran ila te synthetase activity. N one of the analogues was efficiently incorporated into protein. Only 4 o f the analogues (4-methyl-, 4-fluoro-, 5-fluoroand 5-hydroxytryptophan) were good substra tes for tryptophan decarboxylase while all o ther analogues were ra th e r poor substra tes or were not converted at all. A lpha-m ethyltryptophan was a com petitive in h ib ito r o f tryp tophan de ­ carboxylase.