Inhibition of ent-kaurene synthase by quaternary ammonium growth retardants

The effect of fourteen quaternary ammonium iodides on entkaurene synthase from Cucurbita maxima L. was examined. Structure-dependent inhibition of the overall AB activity of entkaurene synthase was found, but only weak or no inhibition on B activity, suggesting that the site of inhibition was ent-kaurene synthase A. N,N,N-Trimethyl-1-methyl-(2',2',4',6'-tetramethyl- cyclohex-3'-en-1'-yl)prop-2-enylammonium iodide, which has structural similarity to geranylgeranyl pyrophosphate, reduced AB activity to 50% of the control value at a concentration of 0.1 mu M.