Substrate-Specific Effect of Oleic Acid and Serum from Patients with Reye's Syndrome on Respiratory Control Ratio of Rat Liver Mitochondria

Abstract

The effects of oleic acid and the serum from two patients with Reye's syndrome (RS-serum) on the respiratory control ratio (RCR) of rat liver mitochondria were studied; the reaction site of each reagent was determined by using various substrates for the respiratory chain. The results were as follows: 1. Pre-incubation of rat liver mitochondria with oleic acid induced a decrease in RCR when succinate or ascorbate+cytochrome c were employed as substrates. 2. Under the identical conditions, RS-serum induced a significant decrease in RCR with ascorbate+cytochrome c. 3. When KCN was added to the assay medium, both oxygen consumption rate and RCR were decreased as expected in oxidizing ascorbate+cytochrome c. But the effect of KCN was less obvious when pyruvate+L-malate were employed as substrates. The latter phenomenon might suggest that the rate-limiting step in the electron transport system from NADH to O2 resided on the substrate side and not on the side between coenzyme Q and O2.Among the substrates (succinate, pyruvate+L-malate, ascorbate+N, N, N′, N′-tetramethyl-phenylenediamine, ascorbate+cytochrome c) tested, the strongest effect was observed when ascorbate+cytochrome c were employed as substrates. These results suggest that both oleic acid and RS-serum showed similar substrate-specific inhibition of RCR, predominantly at the site of cytochrome c oxidase. Thus, a localized effect of oleic acid or RS-serum on the mitochondrial respiratory chain became apparent.