Inhibition of succinate oxidation by barbiturates in tightly coupled mitochondria

Abstract

1.1. Polarographic assays showed 1 mM amytal to inhibit oxidation of NAD-linked substrates almost completely, and succinate oxidation in presence of phosphate and ADP by about 30%, but had little effect on the low rates of oxidation found in absence of ADP. Anytal did not affect the stimulation of tetramethyl-π-phenylene-diamine oxidation by ADP.2.2. In manometric assays, amytal inhibited succinate oxidation to a less extent than in the polarographic method, but it stimulated oxygen uptake in absence of phosphate-acceptor system under these conditions. Phosphorylation was inhibited to a greater extent than oxidation.3.3. Amytal inhibition of succinate oxidation was not prevented by 2,4-dinitrophenol or EDTA, although these substances release respiratory control by ADP. It could be prevented (or reversed) by disruption of the mitochondria and by addition of Ca2+. Study of the light-scattering properties of the mitochondria indicated that prevention of amytal inhibition by Ca2+ was associated with a rapid swelling, greater than the reversible swelling shrinkage caused by substrates and ADP, but less extensive than the effects of other disruptive treatments.4.4. These results are discussed in relation to other work which has suggested interference by barbiturates in the energy-transfer sequence of oxidative phosphorylation.