STRUCTURE AND ACTIVITY OF HERBICIDAL INHIBITORS OF PHYTOENE DESATURASE

摘要

Phytoene desaturase is a membrane-bound enzyme in the biosynthetic pathway of carotenoids. This enzyme is the target of herbicidal inhibitors of different chemical structure. The inhibitory properties of appropriate bleaching herbicides were assayed either with algal cells or in a cell-free carotenogenic system using thylakoid membranes from the alga Aphanocapsa. When intact cells are used for determination of I_(50) values, it is important to measure a specific product resulting from the reaction of the inhibited enzyme rather than a secondary parameter like cell growth. Comparison of the in vivo and in vitro systems showed the advantages of both approaches. The herbicides used in this study were m-phenoxybenzamides, o-phenoxynicotinamides, and phenylpyridazinones. Enzyme kinetics with the herbicides mentioned led to the conclusion that the type of inhibition is non-competitive or irreversible in all cases.