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.