Mitochondrial preparations from the leaves of tobacco (Nicotiana tabacum). 2. Oxidative phosphorylation

Abstract

Further properties are described of a sedi-mentable preparation from tobacco leaves which has been shown previously to catalyze many oxidations of the tricarboxylic acid cycle. The oxidation of some substrates was accompanied by an evolution of CO2 which varied in amount between 0.3 and 1.5 times the volume of O2 absorbed. A disappearance of orthophosphate accompanied the oxidations provided that adenosine polyphosphates, glucose and hexokinase were present. The ratio of phosphate disappearing to O2 absorbed (P/O ratio) was generally between 1 and 2. 2.4-Dinitrophenol completely suppressed thephosphate disappearance and had less effect on O2 uptake. During the oxidation of substrate acids there was an increase in the amount of glucose 6-phosphate and nucleotide phosphate present. Incubation of the preparation with [32P]orthophosphate resulted in radioactivity being incorporated into the nucleotide fraction. At least 5 times as much was incorporated in the presence as in the absence of oxidizable substrate.