Inhibition of the state 3 respiration of isolated mitochondria and its implications in comparative studies

Abstract

The initial state 3 rates of respiration of mitochondria from plant tissue and from rat liver are usually less than the state 3 rates obtained after the mitochondria experience several state 3-state 4 cycles.

Reduction of the absolute rate of respiration by decreasing the temperature or increasing the osmolarity of the reaction medium increased both the magnitude of the inhibition and its persistence in subsequent cycles. Under particularly adverse reaction conditions the initial state 3 was depressed to the extent that no distinction was observed in the state 3 and state 4 rates and the mitochondria appeared to have lost respiratory control. Thus, for comparative studies, invalid conclusions regarding the effect of these factors on respiration could be drawn unless the inhibition were removed.

The inhibition was observed with substrates other than succinate and was therefore not attributed to oxaloacetate inhibition of succinate dehydrogenase.

Increasing the amount of ADP added at each cycle did not appreciably reduce the inhibition.

The inhibition of initial state 3 rates was satisfactorily relieved by incubating the mitochondria with substrate, and several cycles of ADP under conditions which increased the absolute rate of respiration. Once relieved of the inhibition, mitochondria could be stored at 0° for several hours without the inhibition being apparent again.