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The mechanism of action of chlorpromazine. 2. Reduced diphosphopyridine nucleotide–cytochrome c reductase and coupled phosphorylation

Year: 1959
Type: article
Abstract: In the previous paper (Dawkins, Judah & Rees, 1959) it was shown that 10-(3-dimethylaminopropyl)-2-chlorophenothiazine (chlorpromazine) was an inhibitor of cytochrome oxidase and also ex- hibited some action against oxidative phosphorylation.During the course of this investigation, it became apparent that chlorpromazine also had a second point of action in the respiratory chain.This paper describes experiments which indicate the site of action of chlorpromazine.Also included are some observations on the barbiturate 5-ethyl-5-isoamylbarbituric acid (Amytal), which has a very similar action (Ernster, 1956).A preliminary communication of these results has been published (Dawkins, Judah & Rees, 1958). METHODSAnimals and enzyme preparations were identical with those described in the previous paper (Dawkins et al. 1959), as were all materials.Mitochondria were subjected to two types of treatment: (1) Pre-incubation in 0 075 M-sucrose for 30 min.at 00.For this, mitochondria were suspended in 0-25M-sucrose so that the mitochondria derived from 1 g. of liver were contained in 1 ml. of suspension.This was diluted with ice-cold water to give a final concentration of 0 075M-sucrose.If required, the mitochondrial concentra- tion was adjusted by dilution with cold 0-075M-sucrose.(2) Pre-incubation in water.The mitochondrial pellets were suspended directly in cold water to make a 10% suspension and this was diluted with cold water as required.The suspension was held at 00 for at least 30 min.before use.The reduction of cytochrome c by fi-hydroxybutyrate and succinate was followed spectrophotometrically, with a Unicam SP. 500 spectrophotometer, by determining the increase in absorption at 550 m,u.The components of the system were as follows: substrate (sodium salt), 33 mm; cytochrome c, 40,uM; inorganic sodium orthophosphate buffer, pH 7-2, 33 mM; NaCN, 0.1 mM; ethylenediamine- tetra-acetic acid (EDTA) neutralized to pH 7-2 with NaOH, mma.Mitochondria were added in a volume of 0-1 ml.Final volume was 3 ml.When reduced diphosphopyridine nucleotide (DPNH) was used as substrate, it was added at a concentration of 0-67 mmr.Measurements * Part 1: Dawkins, Judah & Rees (1959).
DOI: 10.1042/bj0730016
Language: English
Open Access status: bronze
OpenAlex ID: W35785437
FWCI: 6.809
Cites: 15
Cited by: 112
Related to: 10