Effects of chloramphenicol and its isomers and analogues on the mitochondrial respiratory chain

Abstract

The nature of the inhibition of mitochondrial respiration by chloramphenicol isomers and analogues has been examined further to explain differences in their action in several systems. With coupled rat-liver mitochondria, D-threo-chloramphenicol inhibited β-hydroxybutyrate oxidase 50% at 1.3 mM and succinoxidase at 3.5 mM. L-threo-Chloramphenicol inhibited 50% at 3.6 mM and 3.7 mM, respectively. The sensitivity of succinoxidase to D-chloramphenicol was lost on freezing the mitochondria. Chloramphenicol inhibited dinitrophenol-activated ATPase with 50% inhibition at 6 mM for the D-isomer and at 2.2 mM for the L isomer. The inhibition of NADH oxidase of frozen–thawed beef-heart mitochondria by D-chloramphenicol analogues was dependent on the analogues' solubility properties. A relationship which approximates a straight line was obtained by plotting log (1/concentration50% inhibition) against log (solubilityethanol/solubilitywater) indicating that the inhibition was greater for analogues which would partition into an organic phase. The inhibition did not depend on the orientation of the mitochondrial membrane; the NADH oxidase of submitochondrial particles prepared either by sonication or with digitonin had the same sensitivity to the analogues. The inhibition of NADH oxidase by rotenone and amytal fitted into the straight line relationship obtained with the chloramphenicol analogues. Beef-liver glutamic dehydrogenase was inhibited by some of the analogues of chloramphenicol with the same relationship as for the inhibition of NADH oxidase. It was suggested that the inhibition of NADH oxidase and glutamic dehydrogenase depends on the inhibitors reacting with a hydrophobic site on the enzyme.