Time Course of Induction of Cytochrome P-450, NADPH-Cytochrome c Reductase, and Cinnamic Acid Hydroxylase by Phenobarbital, Ethanol, Herbicides, and Manganese in Higher Plant Microsomes

Abstract

The mixed function oxidase trans-cinnamic acid 4-hydroxylase, cytochrome P-450, cytochrome b₅, and NADPH-cytochrome c (P-450) reductase were measured in microsomes from aging artichoke tuber slices exposed to manganese, ethanol, phenobarbital, and the herbicides Chloro-IPC, Dichlobenil, and Monuron. Although the microsomal hydroxylating complex is already induced by the slicing and aging process, 25 millimolar MnCl₂, 4 millimolar phenobarbital, and 300 millimolar ethanol caused a marked increase of hydroxylase activity and cytochrome P-450 content and shifted their time course. The herbicides, 200 micromolar Dichlobenil and 200 micromolar Monuron, were less effective. Chloro-IPC was slightly inhibitory. NADPH cytochrome c reductase was significantly increased only in phenobarbital-treated slices. Cytochrome b₅ was generally the least affected among the parameters being measured. The mechanisms by which these compounds increase cytochrome P-450 content and hydroxylase activity are not yet defined.