Rotenone-Insensitive Malate Oxidation by Isolated Plant Mitochondria

The inhibitory effect of rotenone, and the variability of the inhibition, on malate oxidation by isolated plant mitochondria has been investigated. Under conditions where oxaloacetate removal is enhanced (by transamination with glutamate) the rotenone inhibition is less severe. Where oxaloacetate is allowed to accumulate, inhibition by rotenone is marked. Similarly, under conditions which would tend to increase the steady state level of reduction of the NAD pool (restricting coupled electron flow with oligomycin) rotenone inhibition is severe. It is concluded that the degree of rotenone inhibition is related to factors affecting the equilibrium poise of malic dehydrogenase, and does not necessarily reflect the interaction between rotenone and the respiratory chain. There appears to be no correlation between the effectiveness of rotenone inhibition and mitochondrial malic enzyme activity. Although there may be separate pathways of intramitochondrial NADH oxidation, it appears to be premature to postulate separation or compartmentation of intramitochondrial malate oxidation pathways.