Conversion of P‐450 to P‐420 by Neutral Salts and some other Reagents

Abstract

Exposure of liver microsomes to high concentrations of neutral salts resulted in the conversion of the microsomal hemoprotein, P‐450, to a modified form called P‐420. The efficiency of various salts in causing the conversion obeyed the order known as Hofmeister's lyotropic series of ions, i.e. SCN‐ > I− > Br− > Cl− > SO4–, CH3COO‐ for anions, and Li+ > K+, Na+ for cations. The conversion induced by salts proceeded more rapidly in dithionite‐treated microsomes, in which the hemoprotein was kept reduced, than in aerobic microsomes. Even in the absence of added salts the conversion took place to some extent when pH was moved far from neutrality. The addition of salts narrowed the pH region where the hemoprotein was resistant to the conversion. Guanidine hydrochloride, lysolecithin, and high concentrations of aniline also caused the conversion of P‐450. Although iodine was an effective conversion agent, it caused considerable destruction of the hemoprotein. Based on these and other findings, the structure around the heme group of P‐450 as well as the mechanism of its conversion to P‐420 are discussed. Copyright © 1967, Wiley Blackwell. All rights reserved