Metabolic Processes in Cytoplasmic Particles of the Avocado Fruit. VI. Controlled Oxidations and Coupled Phosphorylations

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Abstract
Cytoplasmic particles showing respiratory control (RC) were isolated from ripe avocado fruit. In contrast to earlier observations, dinitrophenol uncoupled electron transport phosphorylations. Failure to observe uncoupling in earlier work was due to differences in preparative techniques and assay procedures. Oxidative phosphorylation is unstable in these preparations. Substrate level phosphorylations are more tightly coupled than are electron transport phosphorylations, and may account for most of the adenosine triphosphate formed. This condition may explain the observation of good RC with low P/O ratios. Product inhibition of malate oxidation was confirmed. This inhibition was overcome by the addition of glutamate to permit transamination. The oxidation of the a-ketoglutarate formed was prevented by the addition of arsenite. Glutamate was not oxidized directly.