Abstract
The carotenogenic enzyme lycopene β-cyclase is found in bacteria, algae and higher plants. The only purified lycopene cyclase to date, originally from the bacterium Erwinia uredovora, was obtained from transformed Escherichia coli and used for cell-free inhibitor studies. Sulfuryl reagents and argininemodifying compounds did not affect enzyme activity. However, 2-(4-methylphenoxy)triethylamine (MPTA), the piperidine carboxylate AMO 1618 (2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidinecarboxylate methylchloride) and nicotine were effective inhibitors. I50 values for MPTA and nicotine were determined as 12 and 4.8μM, respectively. The type of inhibition of lycopene cyclase by MPTA was non-competitive with respect to the substrate lycopene and also to the cofactor NADH. Except for the sensitivity against sulfuryl reagents, the results on inhibition properties of the E. uredovora lycopene cyclase resemble qualitatively and quantitatively those of the cyanobacterial and higher plant enzyme. Consequently, the expressed and purified lycopene cyclase from this bacterium can be used as a model enzyme to assay potential herbicides which interact with the corresponding plant enzyme.
