Biophysical and Enzymological Studies upon the Interaction of trans‐Cinnamic Acid with Higher Plant Microsomal Cytochromes P‐450

Abstract

The interaction of trans‐cinnamic acid with the cytochrome P‐450 of microsomes derived from washed potato slices has been studied. The washing process increased the specific content of microsomal electron transport components and hence provided a useful material in which to study the interaction. Evidence is presented that the trans‐cinnamic acid interacts with the cytochrome P‐450, and that this interaction is analogous to ‘type I’ interactions of other cytochrome P‐450 systems. This evidence includes the formation of a ‘type I’ substrate binding spectrum, an increased rate of reduction of cytochrome P‐450 by NADPH in the presence of trans‐cinnamic acid, an increased oxygen uptake and NADPH oxidation when trans‐cinnamic acid is added to the microsomes in the presence of NADPH, and a close correlation between biophysical parameters of electron transport in the cytochrome P‐450 system and enzymological parameters of the trans‐cinnamic acid 4‐hydroxylation reaction. The investigation has been extended to cytochrome P‐450 systems of other tissues and it has been found that the trans‐cinnamic acid 4‐hydroxylation reaction cannot account for the presence of most of the cytochrome P‐450 in several tissues. This suggests that other functions of higher plant cytochrome P‐450 chains exist, and that the substrate specificity of the hemoprotein may vary in different plant tissues. Copyright © 1977, Wiley Blackwell. All rights reserved